HK1159753B

HK1159753B - Systems, devices and methods for improving accuracy of biosensors using fill time

Info

Publication number: HK1159753B
Application number: HK12100114.7A
Authority: HK
Inventors: C. Chatelier Ronald; M. Hodges Alastair
Original assignee: Lifescan, Inc.
Priority date: 2009-12-30
Filing date: 2012-01-05
Publication date: 2017-08-25

Description

Systems, devices, and methods for improving accuracy of biosensors using fill time

Cross reference to related patent applications

The present patent application claims priority from U.S. patent application serial No.12/649,594, and continues as part of it, filed on 30.12.2009 under the title "Systems, device and method for improving accuracy of biosensors using fill time", which is hereby incorporated by reference in its entirety.

Technical Field

The present invention relates to determining the concentration of an analyte in a sample, and more particularly to making a more accurate determination of the concentration based on the fill time of the sample.

Background

Analyte detection in physiological fluids (e.g., blood or blood-derived products) is of increasing importance to today's society. Analyte detection assays are suitable for a variety of applications, including clinical laboratory testing, home testing, and the like, where the results of such testing play a significant role in the diagnosis and management of a variety of disease conditions. Analytes of interest include glucose, cholesterol, and the like for diabetes management. With the increasing importance of analyte detection, a variety of analyte detection protocols and devices have been developed for clinical and home use. Some of these devices include electrochemical cells, electrochemical sensors, hemoglobin sensors, antioxidant sensors, biosensors, and immunosensors.

One blood characteristic that can affect analyte detection is hematocrit. The level of hematocrit may vary widely among different populations. By way of non-limiting example, a person with anemia may have a hematocrit level of about 20%, while a newborn may have a hematocrit level of about 65%. Even samples taken from the same individual over different time periods may have different hematocrit levels. In addition, because higher hematocrit can also increase blood viscosity, which in turn can affect other parameters related to analyte detection, it is important to factor the hematocrit effect on the sample in making an accurate analyte concentration determination.

One method of factoring in the different hematocrit levels in a blood sample is to separate the plasma from the blood and then recalculate the concentration of antigen relative to the adjusted plasma volume. For example, separation can be achieved by performing a centrifugation step. Other methods of accounting for the different hematocrit levels in a blood sample include using an average calculated value of hematocrit, or measuring hematocrit and then calculating the concentration of antigen relative to the plasma value in a separate step. However, it is believed that these methods are undesirable at least because they involve undesirable sample handling, take additional time, and/or result in substantial errors in the final determination. In addition, the ambient temperature at which the sample is analyzed can also negatively impact the determination of the concentration of the analyte.

Disclosure of Invention

Applicants have recognized that it would be desirable to develop a method that can obtain more accurate analyte concentration measurements that accounts for a wide range of hematocrit levels and temperatures, and that presents little or no of the attendant problems previously described. Accordingly, systems, devices, and methods for determining the concentration of an analyte in a sample are generally provided. In one exemplary embodiment of a method for determining the concentration of an analyte in a sample, the method includes detecting the presence of a sample in an electrochemical sensor. For example, the electrochemical sensor may comprise two electrodes. For example, the two electrodes may comprise oppositely facing orientations (opposing facing). In other embodiments, the two electrodes may comprise facing orientations (fascinating).

The method further includes determining a fill time of the sample by the two electrodes, and calculating a correction factor based at least on the fill time. The method further includes reacting the analyte between the two electrodes to cause physical transformation of the analyte, and determining the concentration of the analyte from the correction factor via the same two electrodes. For example, the reaction of the analyte may produce an electroactive species that is measured by the two electrodes as a current. In some embodiments, both fill time determination and analyte concentration determination may be determined using the same two electrodes.

In an exemplary embodiment of a method for measuring a corrected analyte concentration, the method includes detecting a presence of a sample in an electrochemical sensor. For example, the electrochemical sensor may comprise two electrodes. For example, the two electrodes may comprise opposing orientations. In other embodiments, the two electrodes may comprise facing orientations.

The method further comprises determining the filling time of the sample by means of the two electrodes. The method also includes reacting the analyte to cause a physical transformation of the analyte. The method further comprises the following steps: the method further includes determining a concentration of a first analyte in the sample using the same two electrodes, and calculating a corrected analyte concentration based on the first analyte concentration and the fill time. In some embodiments, both fill time determination and analyte concentration determination may be determined using the same two electrodes.

In one embodiment, the step of calculating a corrected analyte concentration may comprise calculating a correction factor based on the fill time. In this embodiment, the corrected analyte concentration may be calculated based on the first analyte concentration and the correction factor. In an exemplary embodiment, the correction factor may be determined based on a series of thresholds. For example, the correction factor may be approximately zero when the fill time is less than a first fill time threshold. For another example, the correction factor may be calculated from the fill time when the fill time is greater than a first fill time threshold and less than a second fill time threshold. For another example, the correction factor may be a constant value when the fill time is greater than a second fill time threshold.

In some embodiments, the details of the step of calculating the corrected analyte concentration may be based on whether the concentration of the first analyte in the sample is less than or greater than a threshold value. For example, the step of calculating a corrected analyte concentration may comprise: calculating a sum of the concentration of the first analyte in the sample and the correction factor when the concentration of the first analyte in the sample is less than a threshold. For another example, when the concentration of the first analyte in the sample is greater than a threshold, the step of calculating a corrected analyte concentration may comprise: dividing the correction factor by one hundred and adding one to obtain an intermediate term; and multiplying the intermediate term by the concentration of the first analyte to obtain a fill-time corrected analyte concentration.

In some embodiments of the above method, the fill time of the sample may be determined by: applying an electrical potential between the two electrodes while introducing the sample; measuring a battery current that varies over time; and determining a current fall time from the battery current that varies over time. In this embodiment, the current fall time may correspond to a fill time of the sample. In some embodiments, the step of determining the current drop time may include calculating a maximum negative value of the change in measured battery current over time. In some embodiments, the step of determining the current fall time may comprise calculating a difference between at least two current values, wherein the difference is greater than a first predetermined threshold. In some embodiments, the step of determining the current fall time may comprise calculating a difference between at least two current values, wherein the difference is less than a second predetermined threshold. In some embodiments, the step of determining the current fall time may comprise calculating a slope of the measured current over time, wherein the slope is greater than a third predetermined threshold. In some embodiments, the step of determining the current fall time may comprise calculating a slope of the measured current over time, wherein the slope is less than a fourth predetermined threshold. In some embodiments, the step of determining the current fall time may comprise calculating an inflection point of the measured current over time. The step of measuring the time-varying battery current may include, for example, taking a current measurement approximately every 2 milliseconds and calculating and storing an average current from the current measurements approximately every 10 milliseconds. In some embodiments, the method may further comprise determining a level of hematocrit in the sample based on the fill time of the sample. As a result, the concentration of the antigen can be determined from the determined hematocrit level.

In some embodiments of the above method, the step of detecting the presence of the sample may comprise: applying an electrical potential between the two electrodes, and measuring a change in the value of the current greater than a fifth predetermined threshold. In some embodiments, the step of detecting the presence of the sample may comprise: applying an electrical potential between the two electrodes, and measuring a change in the value of the current less than a sixth predetermined threshold. In some embodiments, the step of detecting the presence of the sample may comprise: applying a generally constant current between the two electrodes; and measuring a change in the electrical potential above a seventh predetermined threshold. In some embodiments, the step of detecting the presence of the sample may comprise: applying a generally constant current between the two electrodes; and measuring a change in the electrical potential that is less than an eighth predetermined threshold. In some embodiments, the step of detecting the presence of the sample may be performed by a microprocessor of the analyte measurement instrument.

The electrochemical cell may include a glucose sensor. In another embodiment, the electrochemical cell may comprise an immunosensor. In this embodiment, the analyte at the concentration to be analyzed may include a C-reactive protein. The analysis sample may comprise blood. In one embodiment, the blood may comprise whole blood. The analyte of which the concentration is to be analyzed may comprise glucose.

In one exemplary embodiment of a method for measuring a corrected analyte concentration, the method includes detecting a presence of a sample in an electrochemical sensor. For example, the electrochemical sensor may comprise two electrodes. The method also includes determining a fill time of the sample using the two electrodes. The method also includes reacting the analyte to cause a physical transformation of the analyte. The method further comprises the following steps: the method further includes determining a concentration of a first analyte in the sample using the same two electrodes, and calculating a corrected analyte concentration based on the first analyte concentration and the fill time. In some embodiments, both fill time determination and analyte concentration determination may be determined using the same two electrodes.

In some embodiments, the details of the step of calculating the corrected analyte concentration may be based on whether the concentration of the first analyte in the sample is less than or greater than a threshold value. For example, the step of calculating a corrected analyte concentration may comprise: a sum of the correction factor and the concentration of the first analyte in the sample when the concentration of the first analyte in the sample is less than a threshold. For another example, when the concentration of the first analyte in the sample is greater than a threshold, the step of calculating a corrected analyte concentration may comprise: dividing the correction factor by one hundred and adding one to obtain an intermediate term; and multiplying the intermediate term by the concentration of the first analyte to obtain a fill-time corrected analyte concentration.

In one exemplary embodiment of an electrochemical system, the system comprises: an electrochemical sensor includes an electrical contact configured to mate with a test meter. The electrochemical sensor includes first and second electrodes and a reagent maintained in a separated relationship. The first and second electrodes can include, for example, opposing orientations. In other embodiments, the first and second electrodes may comprise facing orientations. The system also includes a test meter including a processor configured to receive current data from the test strip when a voltage is applied to the test strip, the processor further configured to determine a corrected analyte concentration based on the calculated analyte concentration and the measured fill time using the same two electrodes. The system may also include a heating element configured to heat at least a portion of the electrochemical sensor. In some embodiments, the test meter can include a data store containing a concentration threshold for an analyte, a first fill time threshold, and a second fill time threshold. In some embodiments, at least one of the electrochemical sensor, the test meter, and the processor are configured to measure a temperature of a sample.

In one embodiment, the electrochemical sensor may be a glucose sensor. In another embodiment, the electrochemical sensor may be an immunosensor. The immunosensor can include a first liquid reagent, a second liquid reagent, and a magnetic bead conjugated to an antigen. In one embodiment, the first liquid reagent may comprise an antibody conjugated to an enzyme in a buffer. The first liquid reagent forms stripes (striped) on the lower electrode and may be dried. The second liquid reagent may comprise ferricyanide in a diluted acid solution, a substrate for the enzyme and a second medium. The second liquid reagent forms a stripe on the lower electrode and may be dried. On the other hand, the magnetic beads may be striped on the upper electrode and dried thereon.

The immunosensor can further include a plurality of chambers, a partition, a vent, and one or more sealing components. The separator may be disposed between the lower electrode and the upper electrode. The plurality of chambers may include a reaction chamber, a detection chamber, and a fill chamber. The reaction chamber may be formed in a partition, and may have the first reagent and the magnetic beads conjugated to the antigen disposed therein. The detection chamber may also be formed in the partition and may have a second reagent disposed therein. The filling chamber may be at least partially formed in one of the upper and lower electrodes and the partition plate, and may be spaced apart from the detection chamber by a distance and may overlap at least a portion of the reaction chamber; the exhaust hole may be at least partially formed in each of the partition plate, the lower electrode, and the upper electrode, and may be spaced apart from the reaction chamber by a distance, and may overlap at least a portion of the detection chamber; in one embodiment, the one or more seal assemblies may be a first seal assembly and a second seal assembly. The first sealing assembly may have a bonded anticoagulant connected to one of the upper and lower electrodes, may be disposed to cover the vent hole, and may be configured to both form a wall of the fill chamber and seal the vent hole. The second sealing member may be coupled to the other of the upper and lower electrodes, may be disposed to cover the exhaust hole, and may be configured to seal the exhaust hole. In one embodiment, the first sealing component is a hydrophilic adhesive tape. At least one of the control unit, immunosensor, and meter can include a configuration to measure a temperature of the sample. The analyte whose concentration is calculated by the system may include a C-reactive protein. The sample introduced into the electrochemical cell may comprise blood. In one embodiment, the blood may comprise whole blood.

The electrochemical sensor may also be a plurality of other analytical devices, including, as non-limiting examples: electrochemical cells, glucose sensors, glucose meters, hemoglobin sensors, antioxidant sensors, biosensors, and immunosensors. In one embodiment, the electrochemical sensor is a glucose sensor. The glucose sensor may include an electrochemical cell having a working electrode and a counter or counter/reference electrode. The working electrode and the counter or counter/reference electrode may be spaced apart by about 500 microns or less. In one embodiment, the spacing between the electrodes is in the range of about 80 microns to about 200 microns. The interval may be determined so as to achieve a desired result, such as substantially achieving a steady state current for a desired time. In one embodiment, the spacing between the electrodes may be selected such that reaction products from the counter electrode reach the working electrode.

The working and counter electrodes or counter/reference electrodes may have a variety of configurations. For example, the electrodes may face each other, they may be substantially opposed with respect to each other, or they may have a side-by-side configuration in which the electrodes are placed approximately in the same plane. The electrodes may have substantially the same corresponding areas. The electrodes may also be planar. In one embodiment, the electrochemical cell includes a working electrode, a counter electrode, and a separate reference electrode. In another embodiment, the electrochemical cell may have two electrode pairs. The electrode pairs can have any combination of working, counter/reference and separate reference electrodes, but in one exemplary embodiment each pair includes a working electrode and a counter or counter/reference electrode. In yet another embodiment, the electrochemical cell can have an effective cell volume of about 1.5 microliters or less. The electrochemical cell may be hollow.

The potential may be applied to the electrodes of the cell by a number of different mechanisms, including, by way of non-limiting example, a meter. The magnitude of the potential may depend on a number of different factors, including, as non-limiting examples, the desired reaction of the sample within the cell. In one embodiment, the magnitude of the potential may be selected such that electro-oxidation of the reduced form sample and electro-reduction of the oxidized form sample is substantially diffusion controlled.

The sample may enter the cell by capillary action. A control unit may be used to determine the fill time of the sample into the cell. In one embodiment, the control unit may comprise a current detector configured to measure a current that varies with time, thereby determining a current drop corresponding to the sample fill time. At least one of the control unit, the electrochemical sensor and the meter may be configured to measure the temperature of the sample or the ambient air within the meter or in the vicinity of the electrochemical sensor attached to the meter.

One exemplary embodiment of a method for measuring antigen in a blood sample may comprise: an immunosensor having two electrodes and a meter coupled to an electrochemical cell is provided such that the meter applies an electrical potential between the two electrodes of the immunosensor. The method may further comprise: a blood sample comprising an antigen is introduced into the immunosensor, an electrical potential is applied between the two electrodes, the fill time of the blood sample is calculated, and the concentration of the antigen is determined from the fill time. The immunosensor can further include a reaction chamber and a detection chamber formed in a separator disposed between the two electrodes, a fill chamber at least partially formed in the separator and one of the two electrodes, and a vent at least partially formed in the separator and the two electrodes. The fill chamber can be spaced a distance from the detection chamber and can overlap at least a portion of the reaction chamber. The vent may be spaced a distance from the reaction chamber and may overlap at least a portion of the detection chamber. The antigen of the blood sample may be a C-reactive protein. The method may further comprise measuring the temperature of the blood sample. As a result, the concentration of the antigen can be calculated from the filling time.

The method for measuring a blood sample may further include providing an antibody-enzyme conjugate in a first buffer and magnetic beads linked to an antigen in a second buffer in the reaction chamber. Ferricyanide, glucose and mediator in a dilute acid solution may be provided in the detection chamber. A first seal on a first side of the vent forming the filling chamber wall may be provided and a second seal on a second side of the vent may be provided. When a blood sample is introduced into the immunosensor, at least a portion of the blood sample introduced into the immunosensor moves from the fill chamber to the reaction chamber.

The method may further comprise opening a vent hole by perforating at least one of the seals after a predetermined time. Perforating at least one seal such that a portion of the blood sample containing the antibody-enzyme conjugate that is not bound to the magnetic beads moves to the detection chamber. Additionally, the method can include catalyzing oxidation of glucose in the detection chamber, which can result in formation of ferricyanide. The current is detected electrochemically from the ferricyanide and the concentration of the antigen in the blood sample can be calculated from the detected signal.

The invention also provides the following technical scheme:

1. an electrochemical system, comprising:

an electrochemical cell having a lower electrode and an upper electrode;

a meter coupled to the electrochemical cell such that the meter applies an electrical potential between the lower electrode and the upper electrode of the electrochemical cell; and

a control unit connected with the meter such that the control unit determines a fill time of a sample introduced into the electrochemical cell and calculates a concentration of an analyte in the sample using the fill time.

2. The electrochemical system of claim 1, further comprising a heating element configured to heat at least a portion of the electrochemical cell.

3. The electrochemical system of claim 1, wherein the electrochemical cell comprises an immunosensor.

4. The electrochemical system of claim 3, wherein the immunosensor further comprises:

a first liquid reagent comprising an antibody conjugated to an enzyme in a buffer, the first liquid reagent forming a stripe on the lower electrode and drying;

a second liquid reagent comprising ferricyanide in a diluted acid solution, a substrate for the enzyme, and an electrochemical mediator, the second liquid reagent being striped on the lower electrode and dried;

magnetic beads conjugated to an antigen, the magnetic beads being striped on the upper electrode and dried thereon;

a separator interposed between the lower electrode and the upper electrode;

a reaction chamber formed in the separator and having the first reagent and the magnetic beads conjugated to the antigen disposed therein;

a detection chamber formed in the partition and having the second reagent disposed therein;

a filling chamber at least partially formed in the separator and one of the upper electrode and the lower electrode, and spaced apart from the detection chamber by a distance, and overlapping at least a portion of the reaction chamber;

a gas discharge hole at least partially formed in each of the separator, the lower electrode, and the upper electrode, and spaced apart from the reaction chamber and overlapping at least a portion of the detection chamber;

a first sealing assembly having an added anticoagulant bonded to one of the lower electrode and the upper electrode, positioned over the vent, and configured to form a wall of the fill chamber and seal the vent; and

a second sealing assembly coupled to the other of the upper electrode and the lower electrode and disposed over the vent and configured to seal the vent.

5. The electrochemical system of claim 4, wherein the first seal component comprises a hydrophilic adhesive tape.

6. The electrochemical system of claim 4, wherein at least one of the immunosensor, the meter, and the control unit includes a configuration for measuring a temperature of the sample.

7. The electrochemical system of claim 4, wherein the analyte comprises a C-reactive protein.

8. The electrochemical system of claim 1, wherein the sample comprises blood.

9. The electrochemical system of claim 8, wherein the blood comprises whole blood.

10. A method for measuring a blood sample, comprising:

providing:

an immunosensor having two electrodes; and

a meter coupled to the immunosensor such that the meter applies an electrical potential between two electrodes of the immunosensor;

introducing a blood sample containing an antigen into the immunosensor;

applying an electrical potential between the two electrodes;

calculating a fill time of said blood sample; and

determining the concentration of the antigen from the fill time.

11. The method of claim 10, wherein the immunosensor further comprises:

a reaction chamber and a detection chamber formed in a separator interposed between the two electrodes;

a filling chamber at least partially formed in the separator and one of the two electrodes, at a distance from the detection chamber, overlapping at least a portion of the reaction chamber; and

a gas discharge hole at least partially formed in the separator and the two electrodes, spaced apart from the reaction chamber by a distance, and overlapping at least a portion of the detection chamber;

the method further comprises the following steps:

providing:

an antibody-enzyme conjugate in a first buffer in the reaction chamber and magnetic beads linked to an antigen in a second buffer;

ferricyanide, glucose and mediator in dilute acid in the detection chamber;

a first seal covering a first side of the vent forming a wall of the fill chamber; and

a second sealing member covering a second side of the vent hole,

wherein at least a portion of the blood sample is moved from the fill chamber to the reaction chamber upon introduction of the blood sample into the immunosensor;

after a predetermined time, opening the vent by puncturing at least one of the first and second seals, thereby allowing a portion of the blood sample comprising the antibody-enzyme conjugate that is not bound to the magnetic bead to move to the detection chamber;

catalyzing oxidation of glucose in the detection chamber, which results in formation of ferricyanide;

electrochemically detecting the current from the ferrocyanide; and

determining the concentration of said antigen in said blood sample based on the detected signal.

12. The method of claim 10, wherein calculating the fill time further comprises:

applying an electrical potential between the working electrode and the counter electrode upon introduction of the sample;

measuring a battery current that varies over time; and

determining a current drop time from the cell current as a function of time, wherein the current drop time corresponds to a fill time of the sample.

13. The method of claim 10, further comprising: determining a level of hematocrit in the sample as a function of the fill time of the sample, wherein the determination of the antigen concentration is made as a function of the determined level of hematocrit.

14. The method of claim 10, wherein the antigen comprises a C-reactive protein.

15. The method of claim 10, further comprising:

the temperature of the blood sample is measured.

16. A method of determining the concentration of an analyte in a sample, the method comprising:

detecting the presence of the sample in an electrochemical sensor, the electrochemical sensor comprising two electrodes;

determining a fill time of the sample using the two electrodes;

calculating a correction factor based at least on the fill time;

reacting an analyte between the two electrodes to cause physical transformation of the analyte;

determining the concentration of the analyte from the correction factor using the same two electrodes.

17. The method of claim 16, wherein the step of determining the fill time of the sample comprises:

applying an electrical potential between the two electrodes upon introduction of the sample;

measuring the current as a function of time; and

determining a current fall time from the current as a function of time, wherein the current fall time corresponds to a fill time of the sample.

18. The method of claim 17, wherein determining the current fall time comprises calculating a maximum negative value of the change in measured current over time.

19. The method of claim 17, wherein determining the current fall time comprises calculating a difference between at least two current values, wherein the difference is greater than a first predetermined threshold.

20. The method of claim 17, wherein determining the current fall time comprises calculating a difference between at least two current values, wherein the difference is less than a second predetermined threshold.

21. The method of claim 17, wherein determining the current fall time comprises calculating a slope of the measured current over time, wherein the slope is greater than a third predetermined threshold.

22. The method of claim 17, wherein determining the current fall time comprises calculating a slope of the measured current over time, wherein the slope is less than a fourth predetermined threshold.

23. The method of claim 17, wherein determining the current fall time comprises calculating an inflection point of the measured current over time.

24. The method of claim 16, wherein detecting the presence of the sample comprises:

applying an electric potential between the two electrodes, an

A change in the current value greater than a fifth predetermined threshold is measured.

25. The method of claim 16, wherein detecting the presence of the sample comprises:

applying an electric potential between the two electrodes, an

A change in the current value less than a sixth predetermined threshold is measured.

26. The method of claim 16, wherein detecting the presence of the sample comprises:

applying a generally constant current between the two electrodes; and

a change in the electrical potential greater than a seventh predetermined threshold is measured.

27. The method of claim 16, wherein detecting the presence of the sample comprises:

applying a generally constant current between the two electrodes; and

a change in potential less than an eighth predetermined threshold is measured.

28. The method of claim 16, wherein detecting the presence of the sample is performed by a microprocessor of an analyte measurement instrument.

29. The method of claim 16, wherein the reaction of the analyte produces an electroactive species that is measured by the two electrodes as an electrical current.

30. The method of claim 16, wherein the two electrodes comprise oppositely facing orientations.

31. The method of claim 16, wherein the two electrodes comprise facing orientations.

32. The method of claim 16, wherein the electrochemical sensor comprises a glucose sensor.

33. The method of claim 16, wherein the electrochemical sensor comprises an immunosensor.

34. The method of claim 16, wherein the sample comprises blood.

35. The method of claim 16, wherein the sample comprises whole blood.

36. A method of measuring a corrected analyte concentration, the method comprising:

detecting the presence of a sample in an electrochemical sensor, the electrochemical sensor comprising two electrodes;

determining a fill time of the sample with the two electrodes;

reacting an analyte to cause a physical transformation of the analyte;

determining the concentration of a first analyte in the sample using the same two electrodes; and

calculating a corrected analyte concentration based on the first analyte concentration and the fill time.

37. The method of claim 36, wherein the step of calculating a corrected analyte concentration comprises:

calculating a correction factor based on the fill time, wherein the corrected analyte concentration is calculated based on the first analyte concentration and the correction factor.

38. The method of claim 37, wherein the correction factor comprises about zero when the fill time is less than a first fill time threshold.

39. The method of claim 37, wherein the correction factor is calculated from the fill time when the fill time is greater than a first fill time threshold and less than a second fill time threshold.

40. The method of claim 37, wherein the correction factor comprises a constant value when the fill time is greater than a second fill time threshold.

41. The method of claim 37, wherein the step of calculating a corrected analyte concentration comprises: calculating a sum of the correction factor and the concentration of the first analyte in the sample when the concentration of the first analyte in the sample is less than a threshold.

42. The method of claim 37, wherein when the concentration of the first analyte in the sample is greater than a threshold, the step of calculating a corrected analyte concentration comprises:

dividing the correction factor by one hundred and adding one to obtain an intermediate term; and

multiplying the intermediate term by the concentration of the first analyte to obtain a fill-time corrected analyte concentration.

43. The method of claim 36, wherein determining the fill time of the sample comprises:

applying an electrical potential between the two electrodes while the sample is introduced;

measuring the current as a function of time; and

determining a current fall time from the current that varies over time, wherein the current fall time corresponds to a fill time of the sample.

44. The method of claim 43, wherein determining the current fall time comprises: the maximum negative value of the change in the measured current over time is calculated.

45. The method of claim 43, wherein determining the current fall time comprises calculating a difference between at least two current values, wherein the difference is greater than a first predetermined threshold.

46. The method of claim 43, wherein determining the current fall time comprises calculating a difference between at least two current values, wherein the difference is less than a second predetermined threshold.

47. The method of claim 43, wherein determining the current fall time comprises calculating a slope of the measured current over time, wherein the slope is greater than a third predetermined threshold.

48. The method of claim 43, wherein determining the current fall time comprises calculating a slope of the measured current over time, wherein the slope is less than a fourth predetermined threshold.

49. The method of claim 43, wherein determining the current fall time comprises calculating an inflection point of the measured current over time.

50. The method of claim 36, wherein detecting the presence of the sample comprises:

applying an electric potential between the two electrodes, an

51. The method of claim 36, wherein detecting the presence of the sample comprises:

applying an electric potential between the two electrodes, an

52. The method of claim 36, wherein detecting the presence of the sample comprises:

applying a generally constant current between the two electrodes; and

53. The method of claim 36, wherein detecting the presence of the sample comprises:

applying a generally constant current between the two electrodes; and

a change in potential less than an eighth predetermined threshold is measured.

54. The method of claim 36, wherein detecting the presence of the sample is performed by a microprocessor of an analyte measurement instrument.

55. The method of claim 36, wherein the reaction of the analyte produces an electroactive species that is measured by the two electrodes as an electrical current.

56. The method of claim 36, wherein the two electrodes comprise oppositely facing orientations.

57. The method of claim 36, wherein the two electrodes comprise facing orientations.

58. An electrochemical system, comprising:

(a) an electrochemical sensor including an electrical contact configured to mate with a test meter, the electrochemical sensor comprising:

(i) a first electrode and a second electrode in spaced apart relation, and

(ii) a reagent; and

(b) the test meter including a processor configured to receive current data from a test strip when a voltage is applied to the test strip, the processor further configured to determine a corrected analyte concentration based on the calculated analyte concentration and the measured fill time using the same two electrodes.

59. The electrochemical system of claim 58, wherein the test meter comprises a data store containing a concentration threshold for an analyte, a first fill time threshold, and a second fill time threshold.

60. The electrochemical system of claim 58, further comprising a heating element configured to heat at least a portion of the electrochemical sensor.

61. The electrochemical system of claim 58, wherein the electrochemical sensor comprises a glucose sensor.

62. The electrochemical system of claim 58, wherein the electrochemical sensor comprises an immunosensor.

63. The electrochemical system of claim 58, wherein at least one of the electrochemical sensor, the test meter, and the processor are configured to measure a temperature of the sample.

64. The electrochemical system of claim 58, wherein the analyte comprises a C-reactive protein.

65. The electrochemical system of claim 58, wherein the analyte comprises glucose.

66. The electrochemical system of claim 58, wherein the sample comprises blood.

67. The electrochemical system of claim 58, wherein the sample comprises whole blood.

68. The electrochemical system of claim 58, wherein the first electrode and the second electrode comprise oppositely facing orientations.

69. The electrochemical system of claim 58, wherein the first and second electrodes comprise a facing orientation.

Drawings

The invention will be more fully understood from the following detailed description of the embodiments taken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a flow chart of an exemplary method of determining a concentration of an analyte in a sample according to the present invention;

FIG. 2A shows a schematic side elevational view (not to scale) of an exemplary embodiment of an electrochemical cell according to the invention;

fig. 2B shows a plan view of the electrochemical cell of fig. 2A from above;

FIG. 3 shows a schematic cross-sectional view (not to scale) of an exemplary embodiment of a hollow electrochemical cell according to the present invention;

FIG. 4A shows a perspective view of an assembly test according to the present invention;

FIG. 4B shows an exploded perspective view of an unassembled test strip according to the present invention;

FIG. 4C shows an enlarged perspective view of a proximal portion of a test strip according to the present invention;

FIG. 5A illustrates a bottom plan view of one embodiment of a test strip disclosed herein;

FIG. 5B illustrates a side plan view of the test strip of FIG. 5A;

FIG. 5C illustrates a top plan view of the test strip of FIG. 5B;

FIG. 5D is a partial side view of a proximal portion of the test strip of FIG. 5C;

FIG. 6 shows an exploded view of an exemplary embodiment of an immunosensor according to the present invention, wherein the immunosensor is configured for use with a control unit having an electrochemical detection system for calculating a fill time;

FIG. 7 shows a graph of current versus time transients obtained using one exemplary embodiment of an electrochemical cell provided herein in conjunction with an exemplary embodiment for testing a plurality of blood samples;

FIG. 8 shows a plot of current versus time transients obtained using another exemplary embodiment of an electrochemical cell provided herein in conjunction with an exemplary embodiment for testing a plurality of blood samples;

FIG. 9 shows a graph of the results of testing a plurality of blood samples using a fixed time method and a variable pre-pulse time method according to one exemplary embodiment;

FIG. 10 shows a plot of fill time versus hematocrit level for a plurality of blood samples provided herein;

FIG. 11 illustrates a test voltage waveform in which a test meter applies a plurality of test voltages over a predetermined time interval;

FIG. 12 shows a plot of the results of testing multiple blood samples without correction for fill time;

FIG. 13A shows the same data as FIG. 12, plotted against hematocrit of a blood sample;

FIG. 13B shows a plot of the data shown in FIG. 12 corrected for fill time, plotted against hematocrit of the blood sample;

FIG. 14 shows a graph of the results of testing a plurality of blood samples in a clinical setting;

FIG. 15 shows a plot of current versus time transient values obtained when blood having a hematocrit in the range of 15% to 72% was loaded into an electrochemical sensor of another exemplary embodiment, in conjunction with an exemplary embodiment provided herein for testing multiple samples;

FIG. 16 shows another plot of the data shown in FIG. 15.

DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION

The following detailed description should be read with reference to the drawings, in which like elements in different drawings are numbered identically. The drawings, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the invention. The detailed description illustrates by way of example, not by way of limitation, the principles of the invention.

The terms "about" or "approximately" as used herein with respect to any numerical value or range denote an appropriate dimensional tolerance that allows a component or collection of elements to accomplish its intended purpose as described herein. In addition, as used herein, the terms "patient," "host," "user," and "subject" refer to any human or animal subject and are not intended to limit the system or method to human use, although use of the subject invention in human patients represents a preferred embodiment.

Certain exemplary embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the devices and methods disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the devices and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments and that the scope of the present invention is defined solely by the claims. Features illustrated or described in connection with one exemplary embodiment may be combined with features of other embodiments. Such modifications and variations are intended to be included within the scope of the present invention.

The disclosed systems and methods are applicable to the determination of multiple analytes in a variety of samples, and are particularly applicable to the determination of analytes in whole blood, plasma, serum, interstitial fluid, or derivatives thereof. In an exemplary embodiment, a glucose test system based on a thin-layer cell design has opposing electrodes and a three-pulse electrochemical detection that is fast (e.g., about 5 seconds or less of analysis time), requires a small amount of sample (e.g., about 0.4 μ L or less), and can provide improved reliability and accuracy of blood glucose measurements. In a reaction cell for analysis of an analyte, glucose in a sample may be oxidized to gluconolactone using glucose dehydrogenase, and an electrochemically active medium may be used to shuttle electrons between the enzyme and the palladium working electrode. More specifically, the reagent layer coating at least one electrode in the reaction cell may include pyrroloquinoline quinone (PQQ) cofactor-based Glucose Dehydrogenase (GDH) and ferricyanide. In another example, enzyme GDH based on a PQQ cofactor can be replaced with enzyme GDH based on a Flavin Adenine Dinucleotide (FAD) cofactor. When blood or control solution is injected into the reaction chamber, glucose is oxidized by gdh (ox) and during this process gdh (ox) is converted to gdh (red) as shown in chemical conversion t.1 below. Note that GDH (ox) refers to the oxidation state of GDH, and GDH (red) refers to the reduction state of GDH.

T.1D-Glucose+GDH(ox)→Gluconicacid+GDH(red)

A potentiostat may be used to apply a three-pulse potential waveform to the working and counter electrodes, resulting in a test current transient for calculating glucose concentration. In addition, additional information obtained from the test current transients may be used to distinguish between sample matrices and correct for fluctuations in the blood sample due to hematocrit, temperature variations, electrochemically active components, and identify possible systematic errors.

In principle, the method of the present invention can be used with any kind of electrochemical cell having separate first and second electrodes and reagent layers. For example, the electrochemical cell may take the form of a test strip. In one aspect, the test strip may include two opposing electrodes separated by a thin separator to define a sample-receiving chamber or region in which the reagent layer is disposed. Applicants note that other types of test strips, including, for example, test strips with co-planar electrodes, can also be used in the methods described herein.

The methods disclosed herein for determining the concentration of an analyte in a sample can be used in conjunction with any sample analysis device and/or system. The system generally includes at least one working electrode and one counter electrode between which an electrical potential may be applied. The sample analysis device may generally be associated with a component (e.g., a meter) for applying an electrical potential between the electrodes. Applicants note that a variety of test meters can be used in the systems and methods described herein. However, in one embodiment, the test meter includes at least one processor, which may include one or more control units configured to perform calculations capable of calculating a correction factor based on at least one measured or calculated parameter, and configured for data classification and/or storage. The microprocessor may take the form of a mixed signal Microprocessor (MSP), such as texas instruments MSP 430. The TIMSP430 may be configured to also perform a portion of the regulator function and the current measurement function. In addition, MSP430 may also include volatile and non-volatile memory. In another embodiment, many of the electronic components may be integrated with the microcontroller in the form of an application specific integrated circuit.

The sample analysis device may also be associated with one or more components capable of measuring the fill time of a sample as it is introduced into the device. The component is also capable of calculating the concentration of the analyte in the sample from the fill time. The components are generally referred to herein as control units. In addition, the terms analyte, antigen, and antibody are used interchangeably herein, and thus, the use of one term applies equally to all three terms, unless otherwise indicated or reasonably known by one of skill in the art.

In one exemplary embodiment of a method for determining the concentration of an analyte in a sample, the sample is introduced into an electrochemical cell of a sample analysis device having a working electrode and a counter electrode. An electrical potential can be applied between the working and counter electrodes of the electrochemical cell and the fill time of the sample into, for example, the capillary space of the electrochemical cell can be determined. The pre-pulse time may be calculated based at least on the fill time of the sample, and the potential may be applied between the working electrode and the counter electrode for the same length of time as the pre-pulse time. The concentration of the analyte in the sample can then be determined. By calculating the pre-pulse time from the fill time, more accurate results for the concentration of the analyte may be achieved. For example, those errors caused by different hematocrit levels throughout the sample may be factored in, and thus a more accurate determination of the concentration of the analyte in the sample may be obtained. As discussed in more detail below, the method may also factor in the temperature effect. In an alternative embodiment for detecting the concentration of an analyte in a sample, the error is corrected on the basis of a determined initial filling speed instead of on the basis of a determined filling time. An example of such a method is disclosed in patent application serial No.12/649,509 entitled "Systems, device and method for measuring hematocrit based on initial fill velocity", filed on 30.12.2009, ronaldc.

In an alternative embodiment, an estimate of the hematocrit level may be determined. In some embodiments, the estimate of the hematocrit level may be determined without reference to the concentration of the analyte of interest. Thus, an assessment relating to a symptom such as anemia may be made. In the system, only hematocrit levels are measured, and no other concentration determinations are made. Determining hematocrit levels based on the teachings of the present disclosure may allow a determination to be made quickly and accurately, typically in less than 1 second. For example, the hematocrit level of a drop of blood can be determined in less than 1 second simply by dropping the blood on the sensor strip of the sample analyzing device. A digital reading of the hematocrit level may be provided almost instantaneously when the blood is placed on the strip.

The fill time can be used in a variety of ways to improve the determination of the concentration of the analyte. For example, the pre-pulse time may be calculated using the fill time of the sample. By adjusting the pre-pulse time according to the fill time, a longer reaction time can be provided for samples that take longer to fill the sensor. For example, if the sample comprises whole blood, the hematocrit level may be a factor in the sample fill time. Adjusting the pre-pulse time in accordance with the fill time may thus allow more accurate concentration values to be determined over a range of hematocrit levels. In some embodiments, the hematocrit level may be related to the fill time, e.g., an estimate of the hematocrit level may be determined based on the fill time. In such instances, the hematocrit level may be factored in during the determination of the concentration of the analyte, thereby providing a more accurate determination of the concentration of the analyte.

In one exemplary embodiment, the steps illustrated in FIG. 1 may be used to determine the concentration of an analyte in a sample. As shown, the sample is first introduced into the device. Any type of sample analysis device may be used in conjunction with at least some of the systems and methods disclosed herein. By way of non-limiting example, these devices may include electrochemical cells, electrochemical sensors, glucose meters, hemoglobin sensors, antioxidant sensors, biosensors, and immunosensors. One exemplary embodiment of a sample analysis device is an electrochemical sensor. The electrochemical sensor may comprise at least two electrodes. The at least two electrodes may be configured in any manner, for example the electrodes may be on the same plane or on different planes. The sample may be introduced into an electrochemical cell.

In one embodiment, the introduction of the sample may be detected by an automated technique, wherein the meter monitors a change in voltage, current, or capacitance that indicates that the sample has been fed into the sample reaction chamber. Alternatively, the physiological sample may be tested by manual techniques, wherein the user visually observes the filling of the sample reaction chamber and initiates the test by pressing a button. In another embodiment, an optical detector in the meter may sense the dosage of the sample. The time taken for the sample to fill the reaction chamber can likewise be measured by any number of similar techniques. In one embodiment, the electrodes may be configured such that, when a sample is introduced into the sensor, the first electrode is brought into contact with the second electrode prior to, or at the same time as, the sample filling the sensor. However, as the sample fills the sensor, the first electrode limits the current it can hold relative to the voltage applied to the second electrode. Whereby the first electrode can limit the current flowing through the electrochemical sensor. Before, simultaneously with or after the sample contacts the first electrode, an electrical potential may be applied between the electrodes such that an electrical current flows between the first and second electrodes when they are bridged by the sample fluid. In one embodiment of the method disclosed herein, the current versus time response during sensor filling can be used to determine the point at which the sensor is sufficiently filled. For example, sufficiently filled may mean that a sufficient amount of liquid has filled the sensor as a whole covering at least the first electrode. In some embodiments, the current versus time response may be: the rate of change of current is discontinuous over time, e.g. the magnitude of the decrease in current increases or the rate of increase decreases. An example of such a method is disclosed in U.S. patent application serial No.12/885,830 to Kranendonk et al, entitled "apparatus and method for improving the measurement of a monitoring device", filed on 9/20/2010, the entire contents of which are hereby incorporated by reference.

In one embodiment of the methods disclosed herein, a potential of about +10mV to about +30mV may be applied across the first and second electrodes of the electrochemical cell for a period of time, such as about 1000ms, while the electrochemical cell is being filled with a sample introduced into the device. In one exemplary embodiment, a potential of about +20mV may be applied between the first and second electrodes as the sample is introduced into the device to fill the cell. The current flowing between the electrodes may be measured at predetermined intervals during this time. For example, the current may be measured every 2 milliseconds ("ms") and the average current stored every 10 ms. This current data can then be analyzed, for example, by the control unit. In some embodiments, the control unit may comprise a microprocessor. As the sample fills the device, analysis of the current data measured over approximately 1000ms may include determining the latest time at which the current has dropped by a predetermined amount. This time can be used as the Filling Time (FT) of the sample. For example, in one embodiment, the latest time that the current has dropped more than 0.4 microamperes ("μ A") within a 40ms interval can be used to determine when the sample has filled the cell.

In some embodiments, the step of determining the current fall time may comprise: a difference between the at least two current values is calculated, the difference being greater than or less than a predetermined threshold. Various predetermined thresholds may be employed. For example, when the working electrode has an area of about 4.2 square millimeters and the hematocrit is determined to be up to about 75%, the predetermined threshold may be in the range of about 0.4 microamperes for a period of about 40 ms. In another exemplary embodiment, the predetermined threshold may be in a range of about 0.7 microamperes to about 0.9 microamperes for a period of about 50ms when the area of the working electrode is about 4.2 square millimeters and the hematocrit is determined to be up to about 60%. In some embodiments, the step of determining the current fall time may comprise: the inflection point of the measured current is calculated as a function of time.

In some embodiments, the step of detecting the presence of the sample may comprise applying an electrical potential between the two electrodes and measuring a change in the value of the current that is greater than or less than a predetermined threshold. Various predetermined thresholds may be employed. For example, when the area of the working electrode is about 4.2 square millimeters, the predetermined threshold may be in the range of about 3 microamps. In other embodiments, the step of detecting the presence of the sample may comprise: a substantially constant current is applied between the two electrodes and the change in potential above or below a predetermined threshold is measured. For example, the predetermined threshold may be in the range of about 200 mV. In other exemplary embodiments, the threshold may be about 400 mV.

After the cell is filled with the sample, a first potential having a first polarity may be applied between the first and second electrodes and the resulting current measured as a function of time. For example, the first potential may refer to a pre-pulse. In some embodiments, the length of time that the pre-pulse may be applied may be about 5 seconds. In other embodiments, the Fill Time (FT) of the sample, which may be determined using any of the techniques described above, may be used to calculate the length of time that the pre-pulse may be applied. For example, the time period may refer to a pre-pulse time (PPT). For example, the pre-pulse time may be calculated such that a sample that takes longer to fill the sensor has a longer pre-pulse time. In one embodiment, the pre-pulse time may be set according to the following exemplary parameters. For example, the pre-pulse time may be calculated according to the following equation:

PPT(ms)＝3000+(FT-300)×9.3

for calculation purposes, for a fill time of less than 300ms, the fill time may be set to 300 ms. This calculation allows the pre-pulse time (PPT) to be adjusted so that samples that take more than a predetermined amount of time, such as about 300ms, to fill the sensor have a longer reaction time. For the purpose of simplifying the calculation and for setting the boundary on the total test time, a maximum pre-pulse time may be set if the filling time is longer than a predetermined time length. For example, in one embodiment, if the fill time is greater than about 500ms, such as about 515ms, the pre-pulse time (PPT) may be set equal to 5000 ms. Thus, in the exemplary embodiment, the minimum PPT (for a fill time of less than about 300 ms) is 3000ms and the maximum PPT (for a fill time of greater than about 500ms, e.g., about 515 ms) is about 5000 ms. In other embodiments, the calculated pre-pulse time may be adjusted to account for other characteristics and requirements of a particular sample or analyte. For example, the variables and constants used to calculate the pre-pulse in the equations shown above may be adjusted to provide alternating maximum and minimum pre-pulses, or a combination thereof.

After the pre-pulse time is determined, a potential can be applied across the cell electrodes at a time equal to the pre-pulse time (PPT), and the resulting current measured changes over time. At least a portion of this data (current over time) provides a first time-current transient value. The first potential may be sufficiently negative relative to the second electrode such that the second electrode functions as a working electrode in which a limited oxidation current may be measured. After the first time interval has elapsed, a second potential may be applied between the first and second electrodes for a second time interval. The second potential causes a current to be measured as a function of time, thereby generating a second time-current transient value. In one embodiment, the second potential has a second polarity opposite the first polarity. For example, the second potential is sufficiently large relative to the positive value of the second electrode such that the first electrode functions as a working electrode in which a limited oxidation current can be measured. In one exemplary embodiment, the first potential and the second potential may range from about-0.6V to about + 0.6V. In one embodiment, the time interval for the time-current transient value may range from about 1 to 10 seconds, preferably from about 1 to 5 seconds. In another embodiment, the sum of the first time interval and the second time interval is less than about 5 seconds. It should also be noted that the first time interval may not necessarily be the same as the second time interval. In one embodiment, the second potential is applied immediately after the first potential is applied. In an alternative embodiment, a time-delayed or open-circuit potential is introduced between the first potential and the second potential. In another alternative embodiment, a time delay is introduced after the physiological sample is detected in the sample reaction chamber and before the first potential is applied. The delay time may range from about 0.01 to about 3 seconds, preferably from about 0.05 to about 1 second, and most preferably from about 0.5 to about 0.9 seconds.

In one exemplary embodiment, the first test potential time T may be₁Applying a first test potential E between the electrodes within PPT milliseconds, for example₁. For example, a potential of +300mV may be applied. After the first test potential time T₁For example, PPT milliseconds later, a second test potential interval T may be provided₂Applying a second test potential E between the electrodes₂For example, -300mV is applied over 1000 ms. At T₁And T₂In this way, a time-varying battery current, referred to herein as a time current transient or current transient, can be measured over a first test potential time interval T₁Is marked as i_a(T) at a second test potential time interval T₂Is marked as i_b(t) of (d). For example, the current over time may be measured every 10ms and the average current stored every 50 ms. At least a portion of the data from the first and second potentials (time-varying current) may provide first and second time-current transient values. The concentration of the analyte in the sample can then be determined from the current data using any number of algorithms.

An example of an algorithm for determining the concentration of an analyte can be found at least in U.S. patent application serial No.11/278,341 to Chatelier et al, entitled "methods and apparatus for analyzing a sample in the presence of an interferent", filed 3.31.2006, the entire contents of which are hereby incorporated by reference. In one exemplary embodiment, the current data is analyzed using a "corner-corrected algorithm without correction" similar to those disclosed in the aforementioned patent applications. In one embodiment, the concentration of the analyte may be calculated using the algorithm shown in equation (Eq.) 1.

Equation 1

In equation 1, G is the concentration of the analyte, i_l、i_rAnd i₂Is the current value, the terms p, zgr, and a are empirically derived correction constants.

In one embodiment of the invention, p may be in the range of about 0.2 to about 4, preferably about 0.1 to about 1. The correction factor a may be used to take into account possible variations in the size of the electrochemical cell. Variations in the size of the electrochemical cell may cause a proportional shift in the magnitude of the measured current. In some cases, the manufacturing process may result in the electrode area of one batch of test strips being different from the electrode area of another batch of test strips. Calculating the correction factor for each batch of test strips helps to offset variations in cell height and electrode area. This term a can be calculated during calibration of the test strip lot.

The correction factor zgr is used to factor in the changes in the background. The presence of an oxidizable species in the reagent layer of the cell prior to addition to the sample may trigger a background signal. For example, if the reagent layer contains a small amount of ferricyanide (e.g., a reducing mediator) before the sample is added to the test strip, the measured test current will increase, which is not attributable to the concentration of the analyte. Since this will result in a constant deviation of the total measured test current for a particular lot of test strips, the deviation can be corrected using the correction factor Z. Similar to terms p and a, Z can also be calculated during the correction process. An exemplary method for calibrating a test strip lot is described in U.S. Pat. No.6,780,645, which is hereby incorporated by reference in its entirety.

In one exemplary embodiment, p may be 0.51, a may be 0.2, and zgr may be 5. Although the methods disclosed herein are described using correction factors: p, a and zgr, but those skilled in the art will appreciate that their use is not essential. For example, in one embodiment, p, a, and/or Z may not be used for the calculation of the glucose concentration (in equation 1, p and/or a may be set equal to one, and zgr may be set equal to zero). The derivation of equation 1 can be found in co-pending U.S. patent application No.11/240,797 entitled "method and apparatus for rapid electrochemical analysis", filed 30/9/2005, the entire contents of which are hereby incorporated by reference.

The current value i can be calculated from the second current transient value_rThe current value i can be calculated from the first current transient value_l. All current values (e.g., i) described in equation 1 and subsequent equations_r、i_lAnd i₂) The absolute value of the current may be used. In some embodiments, the current value i_rAnd i_lMay be an integer part of the current value within the time interval of the current transient value, the sum of the current values within the time interval of the current transient value, or the average current value or the product of a single current value and the time interval of the current transient value. For the sum of the current values, a series of consecutive current measurements from only two current values to all current values may be added together. The current value i can be calculated as discussed below₂。

For example, in the case where the first time interval is 5 seconds long, i_lAverage current i between 1.4 and 4 seconds in a period of 5 seconds_rThe average current between 4.4 seconds and 5 seconds over a period of 5 seconds may be as shown in equations 2a and 3a below.

Equation 2a

Equation 3a

In another example, where the first time interval is 5 seconds long, i_lCan be the sum of currents from 3.9 to 4 seconds for a long period of 5 seconds, and i_rThe sum of the currents from 4.25 to 5 seconds, which may be a 5 second long period, is shown in equations 2b and 3b below.

Equation 2b

Equation 3b

The current magnitude of the first current transient value can be described as a function of time by equation 4.

Equation 4

Item i_ssIs to apply a first test potential E₁The latter steady-state current, D is the diffusion coefficient of the medium and L is the thickness of the separator. It should be noted that in equation 4, t refers to the first test potential E₁Time elapsed after being applied. The current magnitude of the second current transient value can be described as a function of time by equation 5.

Equation 5

There are two differences in the exponential term in equation 5 compared to the exponential term in equation 4, since the first test potential E is different from the second test potential E₁Of opposite polarity₂The second current transient value is generated at the first test potential E₁Immediately thereafter. It should be noted that t in equation 5 refers to applying the second test potential E₂The time elapsed thereafter.

The first test potential may be time-spaced by T₁Inner peak current is denoted as i_paAnd the second test potential may be time-spaced by T₂Inner peak current is denoted as i_pb. If the first test potential E is applied separately₁And a second test potential E₂The first peak current i is measured in the same short time thereafter, for example in 0.1 second_paAnd a second peak current i_pbEquation 4 may be subtracted from equation 5 to obtain equation 6.

Equation 6i_pb-2i_pa＝-i_ss

Since i has already been determined_paIs mainly controlled by interferents, so i can be used_pbAnd i_paTogether, the correction factors are determined. For example, i can be used in a mathematical function as shown below_pbAnd i_paTogether, a correction current is determined that is proportional to glucose and is less sensitive to interferents.

Equation 7 derivation to calculate the current i₄The current is proportional to glucose and has a relative fraction of the removed current due to interferents.

Equation 7

Adding item i to numerator and denominator_ssTo make the molecules near zero in the absence of glucose. For currents at times greater than the minimum time, the term i is estimated using equation 8A_ssWhere the appropriate minimum time can be estimated by equation 8B.

Equation 8A

Equation 8B

Wherein i_ssAfter application of a second potentialThe steady-state current, i, is the measured current which changes over time, D is the diffusion coefficient of the redox-active molecules, wherein this coefficient can be determined from the fick's first law, i.e. J (x, t) ═ -DdC (x, t)/dx, L is the separator thickness, t is the time at which the second potential is applied, wherein at the beginning of the second time interval t is 0.

In one exemplary embodiment, the current value i may be calculated according to equation 9₂。

Equation 9

Equation 1 thus enables accurate measurement of the concentration of an analyte in the presence of an interferent.

As described above, an estimate of the hematocrit level may be determined without reference to the concentration of the analyte of interest. For example, the hematocrit level in a drop of blood can be determined from the current value and the concentration of the analyte. In one exemplary embodiment, the estimate of hematocrit (H) may be derived from equation 10.

Equation 10H ═ 162.5log (i)_r)+119.1log(G)+235.4

In some embodiments, the concentration (G) value of the analyte may be corrected based on the hematocrit level, for example, using equations 11A and 11B.

Equation 11 AG' ═ G + Corr for G < 100mg/dL

Equation 11BG ═ G (1+ Corr/100) for G ≧ 100mg/dL

In equations 11A and 11B, the correction factor Corr may be calculated using a sine function whose amplitude varies with H. For example, at values of H < 30%, Corr can be calculated using the following equation.

Equation 12ACorr ═ 0.4(30-H) sin (π G/400) for G < 400mg/dL

Equation 12BCorr 0 for G ≧ 400mg/dL

Wherein the range of Corr is limited to 0 to-5.

At H > 50%, an "asymmetric sine function" may be used, in which the positive and negative lobes are different. However, the function is continuous so that there are no sudden steps in the correction. For example, equations 13A through 13C may be used to calculate Corr for H > 50%.

Equation 13ACorr ═ 0.2(H-50) sin (π G/180) for G < 180mg/dL

Equation 13BCorr ═ 0.5(H-50) sin (π G/180) for 180 ≦ G ≦ 270mg/dL

Equation 13CCorr ═ 0.5(H-50) for G > 270mg/dL

Wherein for G < 180 the range of Corr is limited to 0 to-5 and for G.gtoreq.180 0 to 5.

In another embodiment, the value of the concentration of analyte (G) may be corrected for fill time, for example, using equations 14A (when G < 100mg/dL) and 14B (when G ≧ 100mg/dL) in conjunction with equations 15A, 15B, and 15C, without deriving an estimate of hematocrit (H).

Equation 14 AG' ═ G + Corr for G < 100mg/dL

Equation 14BG ═ G (1+ Corr/100) for G ≧ 100mg/dL

The correction factor Corr in equations 14A and 14B may be calculated based on a series of FT thresholds based on the Fill Time (FT). For example, using two thresholds (Th) of FT₁And Th₂) The following equation can be used to calculate Corr.

Equation 15A if Th₁＜FT＜Th₂If Corr is 50 (FT-Th)₁)

Equation 15B if FT < Th₁If Corr is 0

Equation 15C if FT > Th₂If Corr is 10

In one exemplary embodiment, the threshold Th₁May be about 0.2 seconds, threshold Th₂May be about 0.4 seconds. For example, when blood fills the sensor in less than about 0.2 seconds, the filling behavior can be described as being close to ideal. Fill times of less than about 0.2 seconds typically occur when the hematocrit is sufficiently low, at which point the viscosity of the sample has minimal effect on the fill behavior of the sample. As a result of the low hematocrit, most glucose is believed to be separated into the plasma phase, where it can be rapidly oxidized. In these cases, the glucose result need not be corrected for fill time effects substantially, and the correction factor may be set to zero. Alternatively, when the hematocrit in the sample is high, the viscosity of the sample can affect the fill time of the sample. As a result, the sample may take longer than about 0.4 seconds to fill the sensor. As a result of the high hematocrit, most glucose is believed to be separated into red blood cells, and a lower rate of glucose is oxidized. In these cases, the glucose results may be corrected based on the fill time. However, it may be important not to excessively correct the glucose value, and thus, in an exemplary embodiment, the correction factor may be limited to a maximum of about 10mg/dL of plasma glucose, or about 10% of the signal. An empirically derived linear equation may be used to increase the correction term in the range of about 0 to about 10 as the fill time increases in the range of about 0.2 to about 0.4 seconds.

One exemplary embodiment of a device that may be used in conjunction with at least some of the systems and methods disclosed herein is a glucose sensor. The glucose sensor may comprise an electrochemical cell, such as the cell shown in fig. 2A and 2B. The cell may include a thin strip diaphragm 201 having an upper surface 202 and a lower surface 203, and may further include a cell region 204 defined between a working electrode 206 disposed on the lower surface 203 and an opposing/reference electrode 205 disposed on the upper surface 202. The membrane thickness can be selected to achieve a desired result, such as having reaction products from the counter electrode reach the working electrode. For example, the membrane thickness can be selected such that the electrodes are separated by a distance t, which can be sufficiently close that electrochemical reaction products at the counter electrode can migrate to the working electrode over the test time and a steady state diffusion profile can be substantially achieved. Typically t may be less than about 500 microns, or in the range of about 10 microns to about 400 microns, more particularly in the range of about 80 microns to about 200 microns. In one embodiment, the spacing between the electrodes may be selected such that reaction products from the counter electrode reach the working electrode before the end of the analysis.

The electrodes may also have a variety of configurations. For example, the electrodes may be planar. Additionally, although in the illustrated embodiment electrodes 205 and 206 face and are substantially opposite each other, in other embodiments the electrodes may be adapted to face only each other, they may be substantially opposite each other, or may have a side-by-side configuration in which the electrodes are disposed approximately in the same plane. Examples of different electrode configurations can be found at least in U.S. patent No.7,431,820 to Hodges, filed 10, 14/2003, entitled "electrochemical cell," the entire contents of which are hereby incorporated by reference.

A sample deposition or "target" area 207 may be defined on the upper surface 202 of the membrane 201 and spaced from the cell region 204 a distance greater than the membrane thickness. The membrane 201 may have a diffusion region 208 that may extend between the target region 207 and the cell region 204. Suitable reagents may include redox mediator M, enzyme E, and pH buffer B, each of which may be contained within the cell region 204 of the membrane, and/or between the cell region 204 and the target zone 207. In sensor applications, a drop of blood may be placed in the target area 207 and the blood components may wick toward the cell region 204.

Each of the electrodes 205 and 206 may have a predetermined area. In the embodiment of fig. 2A and 2B, cell region 204 may be defined by edges 209, 210, and 211 of the membrane, which may correspond to the edges of electrodes 205 and 206, and leading edges (relative target areas 207)212, 213 of the electrodes. In an example of the invention, the electrodes may be about 600 angstroms thick and may be about 1mm to about 5mm wide, although a variety of other dimensions and parameters may be used without departing from the scope of the invention.

Alternatively, both sides of the membrane, except for the target area 207, may be covered with a laminate layer 214 (omitted from the top view), which may serve to prevent evaporation of moisture from the sample and provide mechanical durability to the device. It is believed that evaporation of water is undesirable because it concentrates the sample, dries out the electrodes, and cools the solution, which, while the diffusion coefficient can still be estimated in the above manner, affects the diffusion coefficient and slows down the enzyme kinetics.

In an alternative embodiment, as shown in fig. 3, a hollow electrochemical cell is provided for use in conjunction with the systems and methods disclosed herein. The electrodes 305 and 306 may be supported by spaced polymer walls 330 to define a hollow cell. An opening 331 may be provided on one side of the cell and thereby allow the sample to enter the cavity 332. Although a septum may be included in some embodiments, no septum is used in this embodiment. The electrode may have a variety of configurations, at least as described above. By way of non-limiting example, the spacing between the electrodes may be less than about 500 microns, preferably in the range of about 10 microns or about 20 microns to about 400 microns, more preferably in the range of about 80 microns to about 200 microns. The effective cell volume may be about 1.5 microliters or less.

The electrochemical cells of fig. 2A, 2B, and 3 may be used in conjunction with the meters, control units, other components, and steps of the devices, systems, and methods disclosed herein. Additional disclosure relating to the electrochemical cells of fig. 2A, 2B and 3 can be found in U.S. patent No.6,284,125 to Hodges et al, entitled "electrochemical cell", filed 4/17/1998, the entire contents of which are hereby incorporated by reference. For example, an electrochemical cell used in conjunction with the present disclosure may have two electrode pairs. The electrode pair may include any combination of working, counter/reference and reference electrodes alone.

Another exemplary embodiment of a device for use in conjunction with at least a portion of the systems and methods disclosed herein is a sensor as described below and illustrated in fig. 4A through 5D. The sensor may be in the form of a test strip 62 that includes an elongated body 59 extending along a longitudinal axis L from a proximal end 80 to a distal end 82 and having side edges 56 and 58. The body 59 may include a proximal sample reaction chamber 61 that includes electrodes 164 and 166 and reagent 72. The test strip body 59 can also include distally disposed electrical contacts 63 and 67 for electrical communication with a test meter (not shown).

In one aspect, the test strip 62 is formed from a plurality of layers including a first conductive layer 66, a spacer 60, and a second conductive layer 64. In one embodiment, the first and/or second conductive layers 66, 64 may be formed from a variety of conductive materials placed on an insulating sheet (not shown). Separator 60 can be formed from a variety of electrically insulating materials and can include or be formed from an adhesive. Those skilled in the art will appreciate that although a tri-layer test strip is shown, additional conductive or electrically insulating layers may be used to form the test strip body 59.

As shown in fig. 4A to 4C, a proximal sample reaction chamber 61 may be defined by a first conductive layer 66, a second conductive layer 64, and a spacer 60. As described in more detail below, the reaction chamber 61 may also include a reagent 72 and first and second electrodes 166, 164. For example, a cut-out region 68 in the spacer 60 may expose a portion of the second and first conductive layers 64, 66 and thus define the first and second electrodes 166, 164, respectively. The reagent 72 may be in the form of a layer disposed on the first electrode 166.

In one embodiment, the reaction chamber 61 is adapted for analyzing a small volume of sample. For example, the sample reaction chamber 61 may have a volume of about 0.1 microliters to about 5 microliters, preferably about 0.2 microliters to about 3 microliters, and more preferably about 0.3 microliters to about 1 microliter. To accommodate small sample volumes, it is preferable to have the electrodes closely spaced. For example, where the separator 60 defines a distance between the first electrode 166 and the second electrode 164, the height of the separator 60 may range from about 1 micron to about 500 microns, preferably from about 10 microns to about 400 microns, and more preferably from about 40 microns to about 200 microns.

To further reduce the volume of the reaction chamber 61, the longitudinal and/or transverse dimensions of the cutout region 68 and/or the body 59 may be adjusted. For example, test strip body 59 may include cut-out portions 51 and 52 such that the lateral width of reaction chamber 61 is less than the overall width (width at widest point) of test strip body 59. The cut-out portions 51 and 52 may also assist in delivering the sample to the reaction chamber 61. For example, the cut-away portions 51 and 52 may have a shape corresponding to a portion of a user's finger. The cut-out portions 51 and 52 may assist the user in aligning the sample on his/her finger with sample receiving openings (e.g., openings 70) in the side edges 56 and 58 of the body 59 when the user squeezes a drop of blood with a finger prick. Those skilled in the art will appreciate that although two cutout portions are shown, the test strip body 59 may include only a single cutout portion or no cutout portion.

As described above, the proximal portion of the test strip body 59 can include at least one sample delivery port for delivering a sample to the reaction chamber 61. For example, the cut-out region 68 may extend laterally to the side edges 56 and 58 of the test strip body 59 to provide two openings 70 for delivering physiological fluid to the sample reaction chamber 61. When two openings 70 are present, one opening may serve as a sample receiving port for delivering a fluid sample, while the other may serve as a vent. One skilled in the art will appreciate that alternative structures may be used to deliver a sample to the sample reaction chamber 61, including sample receiving ports and/or vent holes located at different locations on the test strip body 59, such as in the first and/or second conductive layers 66 and 64.

In one example, the test strip 62 is adapted to pull the sample into the reaction chamber 61 by capillary action. For example, when a liquid sample (e.g., whole blood) is brought into contact with one of the openings 70, the dimensions and surface characteristics of the reaction chamber 61 and the opening 70 may be adjusted to be suitable for generating capillary force. One skilled in the art will appreciate that the reaction chamber 61 may include additional structures such as beads, porous membranes, and/or other fillers to (assist) generate capillary forces.

As described above, a reagent such as the reagent 72 may be provided in the reaction chamber 61. The composition of reagent 72 may vary depending on the analyte of interest and the desired sample format. In one aspect, reagent 72 includes at least one mediator and an enzyme and is deposited on first electrode 166. A variety of mediators and/or enzymes are within the spirit and scope of the invention. Examples of suitable mediators include, for example, ferricyanide, ferrocene derivatives, osmium bipyridyl complexes, ruthenium (III) hexamethylenetetramine, and quinone derivatives. Examples of suitable enzymes include glucose oxidase, Glucose Dehydrogenase (GDH) based on a pyrroloquinoline quinone (PQQ) co-factor, GDH based on a nicotinamide adenine dinucleotide co-factor, and flavin-adenine dinucleotide based on GDH (FAD-GDH). One exemplary reagent formulation that would be suitable for making reagent layer 72 is described in co-pending U.S. patent application Ser. No.10/242,951, entitled "method of manufacturing a sterilized and calibrated biosensor-based medical device," U.S. patent application publication No.2004/0120848, the entire contents of which are hereby incorporated by reference.

Distal to proximal sample chamber 61, body 59 may include connecting traces that electrically connect first and second electrodes 166 and 164 with distal electrical contacts 63 and 67. In one aspect, first conductive layer 66 includes a first connecting trace 76 that electrically connects first electrode 166 with first electrical contact 67. Similarly, the second conductive layer 64 may include a second connecting trace 78 that connects the second electrode 164 with the second electrical contact 63 (fig. 5A).

The first and second conductive layers may also define first and second electrical contacts 67 and 63 that facilitate electrical contact of the test strip 62 with a test meter. In one embodiment, a portion of the first conductive layer 66 extends distally from the distal ends of the spacer 60 and the second conductive layer 64, thereby defining a first electrical contact 67. A second electrical contact may be defined in the first conductive layer 66 by a U-shaped notch 65 that exposes a portion of the second conductive layer 64. Applicants note that the test strip 62 may include a variety of alternative electrical contact configurations for electrically connecting to a test meter. For example, U.S. patent No.6,379,513 discloses an electrochemical cell connection structure, and is hereby incorporated by reference in its entirety.

The sensors of fig. 4A-5D may be used in conjunction with the meters, control units, other components, and steps of the devices, systems, and methods disclosed herein. Additional disclosure relating to the electrochemical cells of fig. 4A-5D may be found in U.S. patent application serial No.11/278,341(Chatelier et al) entitled "method and apparatus for analyzing a sample in the presence of an interferent," filed at 31.3.month, the entire contents of which are hereby incorporated by reference.

Fig. 6 illustrates another exemplary embodiment of a sample analysis device for use in connection with at least a portion of the methods disclosed herein: immunosensor 110, which is described in U.S. patent application serial No.12/570,268(Chatelier et al) entitled "adhesive compositions for immunosensors" filed on 30/9/2009, the entire contents of which are hereby incorporated by reference. A plurality of chambers may be formed in the immunosensor, including: a fill chamber through which a sample can be introduced into the immunosensor; a reaction chamber through which a sample can be reacted with one or more desired substances; and a detection chamber through which the concentration of a particular component in the sample can be determined. The chambers can be formed in at least a portion of the lower electrode, the upper electrode, and the separator of the immunosensor. The immunosensor can further include a vent for air to enter and exit the immunosensor, if desired, and first and second sealing components for selectively sealing first and second sides of the vent. The first seal assembly may also form a wall of the fill chamber.

As shown, the immunosensor 110 includes a lower electrode 112 having two liquid reagents 130 and 132 formed thereon in stripes. The lower electrode 112 may be formed using a variety of techniques for forming an electrode, but in one embodiment, a barium sulfate-filled polyethylene terephthalate (PET) foil may be sprayed with gold. Other non-limiting examples of forming electrodes are disclosed in U.S. patent No.6,521,110(Hodges et al) entitled electrochemical cell filed on 11/10/2000, the entire contents of which are hereby incorporated by reference.

Likewise, the liquid reagents 130 and 132 may have a variety of different compositions. In one embodiment, the first liquid agent 130 includes a composition comprising sucrose and a poloxamer (e.g., Pluronics)Block copolymers), anticoagulants (e.g., citraconate), and enzymes (e.g., GDH-PQQ) conjugated in a buffer of calcium ions. In one embodiment, the second liquid reagent 132 comprises a mixture of ferricyanide, glucose, and a second mediator (e.g., phenazine ethosulfate) in an acidic buffer (e.g., diluted citraconic acid solution). The first and second liquid reagents 130, 132 may be dried on the lower electrode 112. Various techniques may be used to dry the reagents 130 and 132, but in one embodiment, one or more infrared dryers may be applied to the reagents 130 and 132 after the reagents 130 and 132 are striped on the lower electrode 112. For example, after the use of an infrared dryer, one or more air dryers may also be used. References herein to a first reagent and a first liquid reagent and a second liquid reagent are used interchangeably and do not necessarily indicate that in a particular embodiment, the reagents are in their liquid or dry state at a given time. In addition, some of the components associated with the first and second liquid reagents may be used interchangeably and/or jointly in the first and second liquid reagents as desired. By way of non-limiting example, the anticoagulant can be associated with one or both of the first liquid reagent 130 and the second liquid reagent 132.

A line may be formed at the sprayed gold between the reagents 130 and 132 such that the edge of the reagent 132 is in close proximity to or in contact with the line. The lines can be scribed using laser ablation or a sharp metal blade. In one exemplary embodiment, the lines may be scribed before the reagents 130 and 132 are striped on the electrodes. This line can be designed to electrically insulate the portion of the lower electrode 112 below the detection chamber from the portion that would be below the reaction chamber. This may better define the area of the working electrode during the electrochemical detection analysis.

The immunosensor 110 can also include an upper electrode 114 having one or more magnetic beads 134 with surface-bound antigens contained thereon. The antigen can be configured to react with the antibody disposed on the lower electrode 112 and the sample in the reaction chamber 118, as described in detail below. Applicants note that the components disposed on the lower electrode 112 and the upper electrode 114 are interchangeable. Thus, the lower electrode 112 may include one or more magnetic beads 134 and the upper electrode 114 may include two liquid reagents 130 and 132 striped thereon. Additionally, although in the illustrated embodiment the length of the electrode 112 forms the entire length of the immunosensor 110, in other embodiments the electrode may be only a portion of the immunosensor layer and serve as a lower electrode or an upper electrode, or multiple electrodes may be disposed on a single layer immunosensor. In addition, because the potential applied to the immunosensor can be reversed and/or alternated, each of the lower and upper electrodes can be used as a working electrode and a counter or counter/reference electrode at different stages. For purposes of illustration, in this patent application, the lower electrode is considered to be the working electrode and the upper electrode is considered to be the counter electrode or counter/reference electrode.

The spacer 116 disposed between the upper and lower electrodes 112 and 114 can have a variety of shapes and sizes, but is generally shaped to advantageously engage the lower and upper electrodes 112 and 114 to form the immunosensor 110. In an exemplary embodiment, the spacer 116 includes two-sided adhesive. The separator 116 may also include a release liner on each of the two sides of the separator 116. The partition 116 may be cut in such a manner that at least two cavities are formed. The first cavity formed can serve as the reaction chamber 118 and the second cavity formed can serve as the detection chamber 120. In one embodiment, the partition 116 may be lightly die cut to align the reaction chamber 118 with the electrodes 112 and 114, thereby allowing the antigen and antibody to react therein; and the detection chamber 120 is aligned with the electrodes 112 and 114 to allow electrochemical determination of ferricyanide therein.

In one embodiment, the separator 116 can be disposed on the lower electrode 112 in a manner such that the magnetic beads 134 on the upper electrode 114 and the first reagent 130 on the lower electrode 112 are at least partially disposed in the reaction chamber 118, and the ferricyanide-glucose combination of the second reagent 132 on the lower electrode 112 is at least partially disposed in the detection chamber 120. It may be advantageous to include an anticoagulant in both first liquid reagent 130 and second liquid reagent 132, such that an anticoagulant is associated with each of reaction chamber 118 and detection chamber 120. In some embodiments, the combination of one of the upper and lower electrodes 112 and 114 and the separator 116 can be laminated together to form a double layer laminate, while in other embodiments the combination of each of the lower electrode 112, the upper electrode 114, and the separator 116 can be laminated together to form a triple layer laminate. Alternatively, additional layers may be added.

The fill chamber 122 may be formed by perforating one of the lower and upper electrodes 112, 114 and the separator 116. In the illustrated embodiment, the fill chamber is formed by perforating the lower electrode 112 and the separator 116 such that the holes in the lower electrode 112 overlap the reaction chamber 118. As shown, the fill chamber 122 can be spaced a distance from the detection chamber 120. Such a configuration allows the sample to enter the immunosensor 110 through the fill chamber 122 and then flow into the reaction chamber 118 for reaction, e.g., with the first liquid reagent 130 (containing antibodies conjugated to enzymes in a buffer on the first electrode 112) and the magnetic beads 134 striped on the upper electrode 114, without entering the detection chamber 120. Once reacted, the sample may then flow into the detection chamber 120 to interact with a second liquid reagent 132, such as a mixture of ferricyanide, glucose, and a second medium in an acidic buffer.

The vent 124 may be formed by perforating each of the two electrodes 112 and 114 and the separator 116 such that the vent 124 extends through the entirety of the immunosensor 110. The holes may be formed in any suitable manner (e.g., drilling or punching holes at a number of different locations), but in one exemplary embodiment, the holes may overlap a region of the detection chamber 120 that is separate from the reaction chamber 118.

The vent 124 may be sealed in a number of different ways. In the illustrated embodiment, a first sealing member 140 is positioned on the lower electrode 112 to seal a first side of the vent 124 and a second sealing member 142 is positioned on the upper electrode 114 to seal a second side of the vent 124. The seal assembly may be made of and/or include any number of materials. As a non-limiting example, either or both of the sealing components may be a hydrophilic tape or ScotchA belt. The adhesive side of the sealing assembly may face the immunosensor 110. As shown, the first sealing component 140 may not only form a seal for the vent 124, but may also form a wall of the fill chamber 122 such that a sample may be contained therein. The properties compounded on the adhesive side of the first sealing component 140 may be related to the fill chamber 122. For example, if the first sealing component 140 includes properties that render it hydrophilic and/or water soluble, the fill chamber can maintain good wettability when a sample is disposed therein. In addition, the seal assemblies 140 and 142 can each be selectively coupled to or decoupled from the immunosensor 110 to provide venting and/or sealing of the immunosensor 110 and the components disposed therein as desired.

Adhesives may be used in construction of the immunosensor generally. Non-limiting examples of methods by which the adhesive may be incorporated into an immunosensor and other sample analysis devices of the present invention can be found in U.S. patent application serial No.12/570,268(Chatelier et al) entitled "adhesive compositions for use in an immunosensor," filed on 9, 30, 2009, the entire contents of which have been incorporated by reference.

While the present invention discusses various embodiments relating to immunosensors, other embodiments of immunosensors can be used in conjunction with the methods of the present invention. Non-limiting examples of such embodiments include those described in the following patents: U.S. patent application publication No.2003/0180814 entitled "direct Immunosensor assay" filed on day 3, 21, 2002 (Hodges et al), U.S. patent application publication No.2004/0203137 entitled "Immunosensor" (Immunosensor) filed on day 4, 22, 2004 (Hodges et al), U.S. patent application publication No.2006/0134713 entitled "biosenso rappraratus and methods of use" (biosensor device and methods of use) filed on day 11, 21, 2005 (Rylatt et al), and U.S. patent application serial No. 12/563,091, which claims priority to each of U.S. patent application publications nos. 2003/0180814 and 2004/0203137, the entire contents of which are hereby incorporated by reference.

In one embodiment, the immunosensor 110 can be configured to be placed in a meter configured to apply an electrical potential to the electrodes 112 and 114 and to measure a current resulting from the applied electrical potential. In one embodiment, the immunosensor includes one or more tabs 117 for engaging a meter. Other features may also be used to engage the immunosensor 110 with a meter. The meter may include many different features. For example, the meter may include a magnet configured to hold certain components of the immunosensor 110 in one chamber while other components flow to another chamber. In one exemplary embodiment, the magnet of the meter is positioned such that after the immunosensor 110 is placed in the meter, the magnet is positioned below the reaction chamber 118. This may allow the magnet to help prevent any magnetic beads 134, and more specifically any antibody-enzyme conjugate bound to the beads 134, from flowing into the detection chamber 120.

An alternative feature of the gauge includes a heating element. The heating element can help speed the reaction and help the sample flow through the immunosensor 110 in a desired manner by reducing the viscosity. The heating element may also allow one or more chambers and/or samples disposed therein to be heated to a predetermined temperature. Heating to a predetermined temperature can help provide accuracy, for example, by eliminating or removing the effects of temperature changes as the reaction proceeds.

In addition, a piercing instrument may also be coupled to the gauge. The piercing instrument can be configured to pierce at a desired time on at least one of the first sealing member and the second sealing member such that air can flow out of the vent and liquid can flow from the reaction chamber into the detection chamber.

The immunosensor 110 can also be configured to be coupled to a control unit. The control unit may be configured to perform a variety of functions. In an exemplary embodiment, the control unit is capable of measuring the filling time of the sample when the sample is introduced into the device. In another embodiment, the control unit may be configured to determine a hematocrit value of the blood sample. In a further embodiment, the control unit may be configured to calculate the concentration of the analyte in the sample from the fill time. Indeed, the control unit may comprise a number of different features, at least partly due to the required functionality and the way the system is designed to measure the filling time.

The control unit may also measure other aspects of the system. As a non-limiting example, the control unit may be configured to measure the temperature of one or more chambers of the immunosensor. The control unit may also be configured to measure the temperature of the sample, the color of the sample, or a number of other characteristics and/or properties of the sample and/or the system. As other non-limiting examples, the control unit may be configured to transmit the result of the fill time determination, the result of the concentration determination of the analyte, and/or the result of the hematocrit measurement to an external device. This process can be accomplished in any number of ways. In one embodiment, the control unit may be hard wired to the microprocessor and/or the display device. In another embodiment, the control unit may be configured to wirelessly transmit data from the control unit to the microprocessor and/or display device.

Other components of the system may also be configured to make the above-described measurements. For example, the immunosensor or meter can be configured to measure a temperature in one or more chambers of the immunosensor, to measure or derive a temperature of the sample, or to measure, determine, or derive a variety of other characteristics and/or properties of the sample and/or system. In addition, the applicant has noted that these features of the control units may be interchanged or selectively combined in a single control unit. For example, the control unit may both determine the filling time and measure the temperature of the chamber. In other embodiments, multiple control units may be used together to perform multiple functions, based at least in part on the configuration of the multiple control units and the desired functions to be performed.

Example 1

The following examples will illustrate the use of an electrochemical system to measure fill time. In the following examples, the system comprises a sensor having two opposing electrodes and the predetermined reagent is reacted with the sample dried on one electrode. A plurality of samples are provided for analysis to test the performance of the systems, devices, and methods disclosed herein. The sample is a blood sample containing three different hematocrit levels, which are known so that the test results can be compared to the actual results to determine the accuracy of the system, device and method. The four hematocrit levels were approximately 20%, 60%, and 75%. Testing for three levels of hematocrit allows the accuracy of the systems, devices, and methods of the present invention to be determined over a wide range of concentration levels.

In this example, the electrode covered with the dried reagent is the second electrode. The first and second electrodes cover the entire area of the chamber to be filled with the liquid sample. The sample is introduced into the sensor. Although the introduction of the sample into the sensor can be achieved in a number of ways, in this example, the individual samples are brought into the fill chamber by capillary action. At the beginning of the sample entry into the detection chamber, a potential of 300mV was applied to the electrodes by the meter for about four seconds. Alternatively, the voltage may be applied before the blood enters the detection chamber, or as the blood enters the detection chamber. The transient of current versus time from this example is shown in figure 7. As shown in fig. 7, the line showing the time-current transient obtained with 75% hematocrit blood is relatively flat in about 0.1 to about 0.5 seconds because the filling process increases the first electrode area (which tends to increase the current) while there is electrochemical depletion of the electroactive species at the first electrode (which tends to decrease the current). These two processes are approximately matched when the sensor is filled with blood. After the filling is completed (at about 0.5 s), the first process ends and the second process becomes dominant, causing the current to drop rapidly. The last time the current sharply decreased is taken as the fill time. The results for 20% and 60% hematocrit blood showed similar results, with a drop in current for 60% hematocrit blood at about 0.3s and a drop in current for 20% hematocrit blood at about 0.1 s. The results of this experiment demonstrate the feasibility of using amperometric measurements to determine the percent hematocrit of blood.

Example 2

A second sensor was constructed containing two opposing electrodes and designed to react the reagents with the sample dried on one electrode. However, in this example, the electrode with the dried reagent is the first electrode, which is configured such that it does not cover the entire area of the liquid-filled chamber, while the second electrode is configured such that it covers a larger area of the liquid-filled chamber and contacts the liquid before the first electrode contacts the liquid. When the sensor was used to test multiple blood samples adjusted to multiple hematocrits, the resulting current pattern shown in FIG. 8 was obtained. In this example, the four levels of hematocrit are approximately 30%, 44%, and 62%. As shown in fig. 8, the leading portion of each trace corresponds to the period during which the fill process increases the area of the working electrode and thus the current. At the completion of the filling process, the electrochemical depletion of the electroactive species tends to reduce the current at the time indicated by the arrow in the figure. Again, the time where the current sharply decreases is taken as the filling time. Different configurations of the sensor will result in different fill times versus hematocrit.

Example 3

The use of different pre-pulse times in an electrochemical system is illustrated by the following examples. A regulated gauge was constructed that was able to use the fill time information to vary the pre-pulse time using the methods described above. Initial testing of the novel meter was performed using heparinized capillary blood. Native hematocrit and glucose were tested, and then plasma and 77% blood were tested at native or sensitized (spiked) glucose levels. The strips were tested on the original meter (fixed time) and the meter disclosed above incorporating the variable pre-pulse time algorithm. The data was analyzed using the algorithm described above.

FIG. 9 shows that 77% hematocrit blood gives a negative bias (-19 to-28%) when tested with the original meter (fixed time), but all points are within 15% of the baseline glucose measurement when tested with the variable pre-pulse time meter. One example of a commercially available instrument configured to perform a reference glucose measurement is the yellowSprings Instrument (YSI) glucose analyzer. Table 1 below summarizes the overall statistics for both types of meters.

TABLE 1

As shown in Table 1, the variable time meters perform better in terms of accuracy and precision than the fixed time meters.

Example 4

The following example will illustrate the use of an electrochemical system to determine hematocrit based on fill time. In this example, the system includes a sample analysis device (particularly the immunosensor 110 of fig. 6), a meter configured to apply an electrical potential, and a control unit configured to determine an initial fill rate. Specifically, an electrical potential is applied to the electrodes of the immunosensor 110, the hematocrit level is determined, and then the electrical potential is reversed. The concentration of the analyte is then determined from the determined hematocrit level. The hematocrit level is determined from the fill time of the sample.

A plurality of samples for analysis are provided for testing the systems, devices, and methods disclosed herein. The sample is a blood sample containing C-reactive protein, and the analyte concentration to be determined is thus the concentration of C-reactive protein. The sample contains four different hematocrit levels that are known so that the test results can be compared to the actual results to determine the accuracy of the system, device and method. The four hematocrit levels were approximately 15%, 49%, 60%, and 72%. Testing of four hematocrit levels allows the accuracy of the systems, devices, and methods of the present invention to be determined over a wide range of concentration levels.

In this example, the immunosensor was pre-heated to approximately 37 ℃ prior to introduction of the sample. The meter associated with the immunosensor is configured to perform the preheating, but other alternatives may be used. The sample is then introduced into the immunosensor. Although the introduction of the sample into the immunosensor can be accomplished in a variety of ways, in this example, each sample is separately introduced into the fill chamber by capillary action.

After about two minutes, the venting of the immunosensor is achieved by piercing the first sealing component. The piercing action is performed using the piercing instrument of the meter, which action in turn allows blood to pass from the reaction chamber of the immunosensor to the detection chamber of the immunosensor. At the beginning of the sample entry into the detection chamber, a potential of 300mV was applied to the electrodes by the meter. As described in the above examples, the current versus time transient values were used to determine the fill time of the sample according to the method described above. The fill time versus percent hematocrit plot from this example is shown in fig. 10. In some embodiments, an estimate of hematocrit according to the methods disclosed herein can be used to represent the antigen concentration relative to plasma rather than whole blood, as this is more acceptable in pathology.

As noted above, it may be advantageous in some embodiments to measure only the level of hematocrit. Thus, the first calculation based on the initial current may be the only step required to do the above calculation. The actual determination of the hematocrit level may be determined as soon as possible after the initial current is calculated. Thus, as a non-limiting example, if the initial current is calculated on the basis of an average over the first 50 milliseconds, the level of hematocrit may be determined after the first 50 milliseconds. Thus, the measurement of the hematocrit of a blood sample can be performed in less than 1 second.

Example 5

An exemplary algorithm for correcting analyte measurements based on the fill time of the sample without further derivation and correction of hematocrit is set forth by the following example. In this example, a sensor containing the enzyme FAD-GDH, but not GDH-PQQ, was tested. A blood sample containing glucose was applied to the sensor and the potential waveform shown in fig. 11 was applied. The fill time of the sample is determined during the application of the first potential to the sensor (E1, which in this example is about +20mV) over a period of about 1 second. In this example, the fill time is determined as the period of time from the first detection time of the sample in the sensor to the time at which the maximum value of the rate of change of the current transient value (i.e., the maximum value of i (t) -i (t + dt)) is measured during application of the first potential. The maximum value of i (t) -i (t + dt), i.e. the steepest point of drop in current, corresponds to the moment at which a sufficient volume of sample fills the sensor for the analyte measurement to be performed. The fill time was not estimated within about the first 0.15 seconds after sample detection, since the initial signal was a combination of a rapid current decrease (due to consumption of antioxidant species near the anode) and a slower current increase (with filling of the sensor). When these two velocities match, a pseudo steady state current is achieved and the change in current is minimal while the remainder of the sensor is filled with blood. For this reason, the earliest fill time shown in fig. 11 is about 0.15 seconds.

At application of a first potential (E1, sustainedAbout 1 second), the second test potential E2 of +300mV was applied for about 3 seconds, after which a third test potential E3 of-300 mV was applied. Calculating i using equations 2b and 3b_lAnd i_rThe value of (c). Value i_lIs calculated as the sum of the currents from 3.9 to 4 seconds over a period of 5 seconds, and the value i_rCalculated as the sum of the currents from 4.25 to 5 seconds over a period of 5 seconds. The first glucose concentration in the sample is then calculated using equation 1 above. In this example, the values p, a, and zgr are 0.5796, 0.02722, and 1.8, respectively.

The first glucose concentration is then corrected according to the fill time of the sample according to equations 14A, 14B, 15A, 15B and 15C above, where the two thresholds Th of FT₁And Th₂0.2 seconds and 0.4 seconds, respectively. As will be discussed in the examples below, applicants have found that correcting the glucose measurement results based on the fill time improves accuracy, resulting in less deviation from the baseline data, according to equations 14A, 14B, 15A, 15B, and 15C.

Example 6

The deviation of the concentration from the reference value is illustrated in this example as a function of the sample fill time. Samples ranging from about 0 to about 70% hematocrit were tested using a FAD-GDH sensor according to the algorithm described above, but were not corrected for fill time. Fig. 12 shows that the deviation of the sample from the baseline value of the concentration of the analyte depends on the fill time of the sample. For example, as shown in fig. 12, the more negative the deviation of the sample is with increasing filling time. In other words, the longer the fill time, the less accurate the uncorrected value of the concentration of the analyte of the sample. Therefore, the deviation is clearly related to the sample filling time.

Example 7

The improvement obtained by correcting the concentration of the analyte as a function of the fill time is illustrated in this example. Fig. 13A shows the same data set-up as shown in fig. 12, plotted against the hematocrit range of the sample. Fig. 13B shows the improvement obtained when correcting data according to the fill time, according to equations 14A, 14B, 15A, 15B, and 15C above. As shown in fig. 13A and 13B, the overall SD deviation decreased from 6.2 to 5.7 after the data had been corrected for fill time. Therefore, correcting the fill time according to the above algorithm provides improved accuracy.

Example 8

The accuracy improvement achieved with fill time correction in a clinical setting is illustrated by this example. Fig. 14 shows a plot of bias versus sample fill time data obtained from 311 donors, in a clinical setting, tested with a FAD-GDH sensor according to the algorithm discussed in example 5 above. The fill time correction provides a reduction in overall SD deviation from 5.75 to 5.58 for this data set. The improvement in this clinical data is only limited because most samples fill the sensor in about 0.2 seconds or less and are not corrected by the fill time algorithm.

Example 9

The data in the previous example was obtained at a 50ms data density (i.e., storing one current value every 50 ms). As shown in fig. 15, faster data storage (e.g., 10ms data density) may result in better fill time resolution. Fig. 15 shows current transient values obtained when blood having a hematocrit in the range of about 15% to about 72% was loaded into the sensor. Fig. 16 shows fill time data calculated from the data of fig. 15. Fig. 16 shows the original fill time values as open diamonds, the average of 5 replicates as filled squares, and ± 1SD as vertical bars. As shown in fig. 16, the fill time ranged from about 0.06 seconds to about 0.32 seconds, with higher hematocrit samples filling more slowly. When the data presented in this example were tested for glucose concentration, the overall SD deviation was reduced from 5.08 to 4.71 after correcting the glucose value for fill time using the algorithm discussed in example 5 above.

Applicants note that these nine examples are just nine of many examples of how the teachings contained herein may be implemented and used. In addition, while the methods, systems, and devices disclosed herein are primarily used in connection with determining the concentration of an analyte in a blood sample, and are primarily concerned with accounting for errors that would result from different fill times and different hematocrit levels in a blood sample, applicants note that the teachings contained herein can also be used with a variety of other samples containing analytes, and that a variety of antigens and/or antibodies contained in the samples can be tested.

Applicants note that the various methods, systems, and apparatus rely to some extent on a particular equation, and that the equations provided are generally based on the instance to which the equation is applied. In light of this disclosure, those skilled in the art will be able to adjust the disclosed equations for other situations without departing from the scope of the present invention.

In addition, the methods disclosed herein, e.g., in connection with determining concentrations and using systems and devices, are not limited to a particular step or order of steps unless specifically stated. Those skilled in the art will recognize that the methods may be performed in a variety of sequences, and will also recognize that steps may be modified or added without departing from the scope of the present invention.

Non-limiting examples of some other types of devices that can be used with the methods disclosed herein are detailed in the following patents: U.S. Pat. No.5,942,102(Hodges et al) entitled "electrochemical methods" (electrochemical methods) filed on 7/5/1997, U.S. Pat. No.6,174,420(Hodges et al) entitled "electrochemical cells" (electrochemical methods) filed on 18/5/1999, U.S. Pat. No.6,379,513(Chambers et al) entitled "SensorConnectionMeans" (sensor connection mechanism) filed on 20/9/1999, U.S. Pat. No.6,475,360(Hodges et al) entitled "Heatedelectrochemical cells" (heated electrochemical cells) filed on 11/9/2000, U.S. Pat. No.6,632,349(Hodges et al) entitled "HemoglobionSensor" (hemoglobin sensor) filed on 14/7/2000, U.S. Pat. No.6,632,349(Hodges et al) entitled "Anxgandner et al" (electrochemical methods) filed on 6,946,067/7/14, and U.S. Pat. No. Bedgerons et al (electrochemical methods) entitled "sensor (electrochemical methods) filed on 6,946,067 entitled" electrochemical methods for forming an electrochemical cell (electrochemical method 6,946,067) (electrochemical methods) filed on 3/2002), U.S. patent No.7,043,821(Hodges) entitled "method of predicting short sampling capillary or wicking filling device with wickingfilldevice" (method of preventing capillary or wicking filling device under-sampling) filed on 3.4.2003 and U.S. patent No.7,431,820(Hodges et al) entitled "electrochemical cell" filed on 1.10.2002, each of which is hereby incorporated by reference in its entirety.

Further, to the extent that the disclosure herein is discussed for a device having a particular configuration, a variety of configurations may be used. For example, some configurations that may be used with the present invention include sensors having two electrodes facing each other, sensors having two electrodes in the same plane, and sensors having three electrodes, where the two electrodes are opposite and the two electrodes are in the same plane. These different configurations may occur in any number of devices, including immunosensors and other devices described above.

Various aspects of the devices, systems, and methods may be adjusted and altered as necessary for various determinations without departing from the scope of the present invention. Furthermore, one skilled in the art will appreciate further features and advantages of the invention based on the above-described embodiments. Accordingly, the invention is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety.

Claims

1. A method for determining the concentration of an analyte in a sample, the method comprising:

introducing a sample containing an analyte into an electrochemical cell of a sample analysis device, the electrochemical cell having a working electrode and a counter electrode;

determining the filling time of the sample;

calculating a time based at least on the fill time for applying the potential between the working electrode and the counter electrode;

applying the potential between the working electrode and the counter electrode for a duration equal to the calculated time; and

determining a concentration of the analyte, wherein determining a fill time of the sample comprises:

measuring a battery current that varies over time; and

determining a current drop time from the battery current as a function of time, wherein the current drop time corresponds to a fill time of the sample.

2. The method of claim 1, wherein determining the current fall time is accomplished by calculating a maximum value of a rate of change of a current transient measured over time.

3. The method of claim 1, wherein measuring the battery current over time comprises:

current measurements were taken every 2 milliseconds; and

the average current is calculated and stored on the basis of the current measurement every 10 milliseconds.

4. The method of claim 1, further comprising:

determining a level of hematocrit in the sample as a function of the fill time of the sample.

5. The method of claim 4, wherein determining the analyte concentration comprises calculating the analyte concentration from the determined hematocrit level.

6. The method of claim 1, wherein the sample analysis device comprises a glucose sensor.

7. The method of claim 1, wherein the sample analysis device comprises an immunosensor.

8. The method of claim 1, wherein the sample comprises blood.

9. The method of claim 8, wherein the blood comprises whole blood.

10. An electrochemical system, comprising:

an electrochemical cell having a lower electrode and an upper electrode;

a control unit connected with the meter such that the control unit determines a filling time of a sample introduced into the electrochemical cell and calculates an analyte concentration in the sample using the filling time, wherein the control unit includes a current detector configured to measure a cell current in the sample as a function of time and determine a current drop time corresponding to the filling time of the sample,

wherein determining the fill time of the sample comprises:

applying an electrical potential between the lower electrode and the upper electrode while introducing the sample;

measuring a battery current that varies over time; and

11. The electrochemical system of claim 10, further comprising a heating element configured to heat at least a portion of the electrochemical cell.

12. The electrochemical system of claim 10, wherein the electrochemical cell comprises an immunosensor.

13. The electrochemical system of claim 12, wherein the immunosensor further comprises:

a second liquid reagent comprising ferricyanide, a substrate for the enzyme, and an electrochemical mediator in a diluted acid solution, the second liquid reagent being striped on the lower electrode and dried;

a separator interposed between the lower electrode and the upper electrode;

a reaction chamber formed in the separator and having a first reagent and the magnetic beads conjugated to the antigen disposed therein;

a detection chamber formed in the partition and having a second reagent disposed therein;

a filling chamber at least partially formed in the separator and one of the upper electrode and the lower electrode, spaced apart from the detection chamber, and overlapping at least a portion of the reaction chamber;

a gas discharge hole at least partially formed in each of the separator, the lower electrode, and the upper electrode, spaced apart from the reaction chamber, and overlapping at least a portion of the detection chamber;

a first sealing assembly having an added anticoagulant coupled to one of the lower electrode and the upper electrode, positioned above the vent, and configured to form a wall of the fill chamber and seal the vent; and

a second sealing assembly bonded to the other of the upper and lower electrodes, disposed over the vent, and configured to seal the vent.

14. The electrochemical system of claim 13, wherein the first seal assembly comprises a hydrophilic adhesive tape.

15. The electrochemical system of claim 13, wherein at least one of the immunosensor, the meter, and the control unit includes a configuration for measuring a temperature of the sample.

16. The electrochemical system of claim 13, wherein the analyte comprises a C-reactive protein.

17. The electrochemical system of claim 10, wherein the sample comprises blood.

18. The electrochemical system of claim 17, wherein the blood comprises whole blood.

19. A method for measuring a blood sample, comprising:

providing:

an immunosensor having two electrodes; and

introducing a blood sample containing an antigen into the immunosensor;

applying an electrical potential between the two electrodes;

calculating a fill time of said blood sample; and

determining the concentration of the antigen from the fill time, wherein calculating the fill time further comprises:

applying an electrical potential between the working electrode and the counter electrode upon introduction of the blood sample;

measuring a battery current that varies over time; and

20. The method of claim 19, wherein the immunosensor further comprises:

a gas discharge hole at least partially formed in the separator and the two electrodes, spaced apart from the reaction chamber, and overlapping at least a portion of the detection chamber;

the method further comprises the following steps:

providing:

ferricyanide, glucose and mediator in dilute acid in the detection chamber;

a second sealing member covering a second side of the vent hole,

wherein, upon introduction of a blood sample into the immunosensor, at least a portion of the blood sample is moved from the fill chamber to the reaction chamber;

catalyzing oxidation of glucose in the detection chamber, which results in formation of ferrocyanide;

electrochemically detecting the current from the ferrocyanide; and

21. The method of claim 19, the method further comprising: determining a level of hematocrit in the sample as a function of the fill time of the sample, wherein the determination of the antigen concentration is made as a function of the determined level of hematocrit.

22. The method of claim 19, wherein the antigen comprises a C-reactive protein.

23. The method of claim 19, the method further comprising:

the temperature of the blood sample is measured.

24. A method of determining the concentration of an analyte in a sample, the method comprising:

determining a fill time of the sample using the two electrodes;

calculating a correction factor based at least on the fill time;

reacting an analyte between the two electrodes to cause physical transformation of the analyte; and

determining the concentration of the analyte from the correction factor using the same two electrodes, wherein determining the fill time of the sample comprises:

measuring the current as a function of time; and

25. The method of claim 24, wherein determining the current fall time comprises calculating a maximum value of a rate of change of a current transient measured over time.

26. The method of claim 24, wherein determining the current fall time comprises calculating a difference between at least two current values, wherein the difference is greater than a first predetermined threshold.

27. The method of claim 24, wherein determining the current fall time comprises calculating a difference between at least two current values, wherein the difference is less than a second predetermined threshold.

28. The method of claim 24, wherein determining the current fall time comprises calculating a slope of the measured current over time, wherein the slope is greater than a third predetermined threshold.

29. The method of claim 24, wherein determining the current fall time comprises calculating a slope of the measured current over time, wherein the slope is less than a fourth predetermined threshold.

30. The method of claim 24, wherein determining the current fall time comprises calculating an inflection point of a measured current over time.

31. The method of claim 24, wherein detecting the presence of the sample comprises:

applying an electric potential between the two electrodes, an

32. The method of claim 24, wherein detecting the presence of the sample comprises:

applying an electric potential between the two electrodes, an

33. The method of claim 24, wherein detecting the presence of the sample comprises:

applying a constant current between the two electrodes; and

34. The method of claim 24, wherein detecting the presence of the sample comprises:

applying a constant current between the two electrodes; and

a change in potential less than an eighth predetermined threshold is measured.

35. The method of claim 24, wherein detecting the presence of the sample is performed by a microprocessor of an analyte measurement instrument.

36. The method of claim 24, wherein the reaction of the analyte produces an electroactive species that is measured by the two electrodes as an electrical current.

37. The method of claim 24, wherein the two electrodes comprise oppositely facing orientations.

38. The method of claim 24, wherein the two electrodes comprise facing orientations.

39. The method of claim 24, wherein the electrochemical sensor comprises a glucose sensor.

40. The method of claim 24, wherein the electrochemical sensor comprises an immunosensor.

41. The method of claim 24, wherein the sample comprises blood.

42. The method of claim 24, wherein the sample comprises whole blood.

43. A method of measuring a corrected analyte concentration, the method comprising:

determining a fill time of the sample with the two electrodes;

reacting an analyte to cause a physical transformation of the analyte;

determining a first analyte concentration in the sample using the same two electrodes; and

calculating a correction concentration based on the same two electrodes; and

calculating a corrected analyte concentration based on the first analyte concentration and the fill time, wherein determining the fill time of the sample comprises:

measuring a battery current that varies over time; and

determining a current drop time from a battery current that varies over time, wherein the current drop time corresponds to a fill time of the sample.

44. The method of claim 43, wherein the step of calculating a corrected analyte concentration comprises:

45. The method of claim 44, wherein the correction factor comprises 0 when the fill time is less than a first fill time threshold.

46. The method of claim 44, wherein the correction factor is calculated from the fill time when the fill time is greater than a first fill time threshold and less than a second fill time threshold.

47. The method of claim 44, wherein the correction factor comprises a constant value when the fill time is greater than a second fill time threshold.

48. The method of claim 44, wherein the step of calculating a corrected analyte concentration comprises: calculating a sum of the correction factor and the first analyte concentration in the sample when the first analyte concentration in the sample is less than a threshold.

49. The method of claim 44, wherein when the first analyte concentration in the sample is greater than a threshold, the step of calculating a corrected analyte concentration comprises:

multiplying the intermediate term by the first analyte concentration to obtain a fill-time corrected analyte concentration.

50. The method of claim 43, wherein determining the current fall time comprises: the maximum value of the rate of change of the transient value of the current measured over time is calculated.

51. The method of claim 43, wherein determining the current fall time comprises calculating a difference between at least two current values, wherein the difference is greater than a first predetermined threshold.

52. The method of claim 43, wherein determining the current fall time comprises calculating a difference between at least two current values, wherein the difference is less than a second predetermined threshold.

53. The method of claim 43, wherein determining the current fall time comprises calculating a slope of the measured current over time, wherein the slope is greater than a third predetermined threshold.

54. The method of claim 43, wherein determining the current fall time comprises calculating a slope of the measured current over time, wherein the slope is less than a fourth predetermined threshold.

55. The method of claim 43, wherein determining the current fall time comprises calculating an inflection point of a measured current that varies with time.

56. The method of claim 43, wherein detecting the presence of the sample comprises:

applying an electric potential between the two electrodes, an

57. The method of claim 43, wherein detecting the presence of the sample comprises:

applying an electric potential between the two electrodes, an

58. The method of claim 43, wherein detecting the presence of the sample comprises:

applying a constant current between the two electrodes; and

59. The method of claim 43, wherein detecting the presence of the sample comprises:

applying a constant current between the two electrodes; and

a change in potential less than an eighth predetermined threshold is measured.

60. The method of claim 43, wherein detecting the presence of the sample is performed by a microprocessor of an analyte measurement instrument.

61. The method of claim 43, wherein the reaction of the analyte produces an electroactive species that is measured by the two electrodes as an electrical current.

62. The method of claim 43, wherein the two electrodes comprise oppositely facing orientations.

63. The method of claim 43, wherein the two electrodes comprise facing orientations.

64. An electrochemical system, comprising:

(i) a first electrode and a second electrode in spaced apart relation, and

(ii) a reagent; and

(b) the test meter comprising a processor configured to receive current data from a test strip when a voltage is applied to the test strip, the processor further configured to determine a corrected analyte concentration of a sample applied to the electrochemical sensor based on a calculated analyte concentration of the sample and a measured fill time of the sample using the same two electrodes, wherein the processor is configured to measure the time-varying current data to determine a current fall time corresponding to the fill time of the sample, wherein determining the fill time of the sample comprises:

measuring a battery current that varies over time; and

65. The electrochemical system of claim 64, wherein the test meter comprises a data store including an analyte concentration threshold, a first fill time threshold, and a second fill time threshold.

66. The electrochemical system of claim 64, further comprising a heating element configured to heat at least a portion of the electrochemical sensor.

67. The electrochemical system of claim 64, wherein the electrochemical sensor comprises a glucose sensor.

68. The electrochemical system of claim 64, wherein the electrochemical sensor comprises an immunosensor.

69. The electrochemical system of claim 64, wherein at least one of the electrochemical sensor, the test meter, and the processor are configured to measure a temperature of the sample.

70. The electrochemical system of claim 64, wherein the analyte comprises a C-reactive protein.

71. The electrochemical system of claim 64, wherein the analyte comprises glucose.

72. The electrochemical system of claim 64, wherein the sample comprises blood.

73. The electrochemical system of claim 64, wherein the sample comprises whole blood.

74. The electrochemical system of claim 64, wherein the first and second electrodes comprise oppositely facing orientations.

75. The electrochemical system of claim 64, wherein the first and second electrodes comprise a facing orientation.