HK1146302B - Rapid-read gated amperometry - Google Patents

Description

Fast reading gated amperometry

Reference to related applications

The present application claims priority from U.S. provisional patent application No.61/012729 entitled "Rapid-read GatedAmperometry" filed on 10.12.2007, the contents of which are incorporated herein by reference.

Background

Biosensors provide a means to analyze biological fluids (e.g., whole blood, serum, plasma, urine, saliva, intercellular or intracellular fluids). Typically, biosensors have a measuring device for analyzing a sample residing on a sensor strip. The sample is typically in liquid form and, in addition to being a biological fluid, may be a derivative of a biological fluid, such as an extract, a dilution, a filtrate or a reconstituted precipitate. The analysis performed by the biosensor determines the presence and/or concentration of one or more analytes (e.g., alcohol, glucose, uric acid, lactic acid, cholesterol, bilirubin, free fatty acids, triglycerides, proteins, ketones, phenylalanine, or enzymes) in the biological fluid. The analysis may be useful in the diagnosis and treatment of physiological abnormalities. For example, a diabetic may use a biosensor to determine the glucose level in whole blood in order to adjust food and/or medications.

Biosensors can be designed to analyze one or more analytes, and can use different sample volumes. Some biosensors can analyze a single drop of whole blood, for example, in a volume of 0.25-15 microliters (μ L). The biosensor may be implemented using a desktop, portable, and similar measuring device. The portable measuring device may be hand-held and capable of identifying and/or quantifying one or more analytes in a sample. Examples of portable measuring devices include Ascensia of Bayer HealthCare, Inc. of Tarrytown, N.Y.Andan example of a meter, bench-top measuring device, includes an Electrochemical Workstation (Electrochemical Workstation) available from CHInstores, Inc. of Austin, Texas, USA. Biosensors that have shorter analysis times while having the desired accuracy and/or precision can provide significant benefits to users.

Biosensors may employ optical and/or electrochemical methods to analyze a sample. In some optical systems, analyte concentration is determined by measuring light that interacts with or is absorbed by a light-identifiable species (e.g., an analyte, a reactant, or a product formed by a reaction of a chemical indicator with the analyte). In other optical systems, the chemical indicator fluoresces or emits light in response to the analyte when illuminated by the excitation beam. The light may be converted into an electrical output signal (e.g., current or voltage), which may also be electrochemically processed into an output signal. In either optical system, the biosensor measures and correlates light to the analyte concentration of the sample.

In the electrochemical biosensor, when an input signal is applied to a sample, the analyte concentration is determined from an electrical signal generated by oxidation/reduction or redox reaction of an analyte or a substance corresponding to the analyte. The input signal may be applied as a single pulse, multiple pulses, a sequence or a periodic wave. A redox enzyme (e.g., an enzyme or similar substance) may be added to the sample to enhance electron transfer from the first substance to the second substance during the redox reaction. An enzyme or similar substance can react with a single analyte, thus providing specificity to a portion of the output signal generated. Some specific examples of oxidoreductases and corresponding analytes are given in table 1 below.

TABLE 1

Oxidoreductase (reagent layer)	Analyte
		Glucose dehydrogenase	β -glucose
Glucose oxidase	β -glucose
		Cholesterol esterase; cholesterol oxidase	Cholesterol
Lipoprotein lipase; a glycerol kinase; glycerol-3-phosphate oxidase	Triglycerides
		Lactate oxidase; a lactate dehydrogenase; diaphorase	Lactic acid
Pyruvate oxidase	Pyruvate salt
		Alcohol oxidizing enzymes	Alcohol(s)
Bilirubin oxidase	Bilirubin
		Uricase	Uric acid
Glutathione reductase	NAD(P)H
		Carbon monoxide oxidation reductase	Carbon monoxide

A mediator may be employed to maintain the oxidation state of the enzyme. Some conventional combinations of enzymes and vehicles for specific analytes are given in table 2 below.

TABLE 2

Electrochemical biosensors typically include a measurement device having electrical contacts that connect to wires in a sensor strip. These wires may be made of conductive materials such as solid metals, metal pastes, conductive carbon pastes, conductive polymers, and the like. The lead wires are typically connected to working, counter, reference and/or other electrodes that extend into the sample vessel. One or more wires may also extend into the sample vessel to provide functionality not provided by the electrodes.

In many biosensors, a sensor strip can be used outside, inside, or partially inside the living tissue. When used outside a living tissue, a biological fluid sample is introduced into a sample container in a sensor strip. Before, after or during introduction of the analysis sample, the sensor strip is placed in the measuring device. When used inside or partially inside living tissue, the sensor strip may be continuously immersed in the sample, or the sample may be intermittently introduced onto the sensor strip. The sensor strip may include a container for partially isolating a volume of sample or providing access to the sample. Also, the sample may flow continuously through the sensor strip or be interrupted for analysis.

The measuring device applies an input signal to the wires of the sensor strip through the electrical contacts. The wire transmits the input signal to the sample in the sample container through the electrode. The redox reaction of the analyte generates an electrical output signal based on the input signal. The electrical output signal from the sensor strip can be a current (generated by amperometry or voltammetry), a voltage (generated by potentiometry/amperometry) or an accumulated charge (generated by coulometry). The measurement device may have processing capability to measure and correlate the presence and/or concentration of one or more analytes in the biological fluid with the output signal.

In a common amperometric method, the current is measured during a read pulse of constant potential (voltage) applied to the working and counter electrodes of the sensor strip, and the measured current is used to determine the amount of analyte in the sample. Amperometry measures the rate at which an electrochemically active, and thus measurable, species is oxidized or reduced at or near the working electrode. Many variations of amperometric methods for biosensors are described, for example, in US patents US5620579, US5653863, US6153069 and US 6413411.

A disadvantage of the conventional amperometric method is the non-steady-state nature of the current after the potential is applied. The rate of change of current with respect to time is initially very fast and slows as the analysis proceeds due to the changing nature of the underlying diffusion process. The steady state current cannot be obtained until the depletion rate of the ionized measurable species at the electrode surface equals the diffusion rate. Therefore, the conventional current measurement method of measuring current during the transient period before reaching the steady state condition is not as accurate as the measurement performed during the steady state period.

The measurement performance of the biosensor is embodied in accuracy and/or precision. The improvement in accuracy and/or precision can improve the measurement performance of the biosensor. Accuracy can be expressed in terms of the deviation of the biosensor analyte reading from a reference analyte reading, a greater deviation value indicating less accuracy, and precision can be expressed in terms of the dispersion or variation of the plurality of analyte readings from a mean. The deviation is the difference between the value determined by the biosensor and a recognized reference value and can be expressed as an "absolute deviation" or a "relative deviation". The absolute deviation may be expressed in units of measurement, such as mg/dL, and the relative deviation may be expressed as a percentage of the absolute deviation value relative to a reference value. The reference value can be determined using a standard meter (e.g., YSI2300 STAT PLUS, available from YSIInc., Yellow Springs, Ohio.)^TM) And (4) obtaining.

Many biosensors include one or more methods to correct for errors associated with the analysis. The concentration values obtained from the analysis with errors are inaccurate. Being able to correct these inaccurate analytical values may improve the accuracy of the acquired concentration values. The error correction system may compensate for one or more errors, such as a different hematocrit content of the sample than the reference sample. For example, a common biosensor may be configured to report a glucose concentration that assumes a 40% (V/V) hematocrit of a whole blood sample, regardless of the actual hematocrit of the sample. In these systems, any glucose measurement performed on a whole blood sample having less than or greater than 40% hematocrit will include an error or bias attributable to the "hematocrit effect".

In a common biosensing strip for determining glucose concentration, glucose can be oxidized by an enzyme, after which electrons are allowed to transfer to a vehicle. The reduced mediator is then transferred to the working electrode where it is subjected to electrochemical oxidation. The amount of mediator that is oxidized may be correlated to the current between the working and counter electrodes of the sensor strip. Quantitatively, the current measured at the working electrode is directly proportional to the diffusion coefficient of the mediator. The hematocrit effect hinders this process because red blood cells impede the diffusion of the mediator to the working electrode. Thus, the hematocrit effect affects the amount of current measured at the working electrode without any relationship to the amount of glucose in the sample.

Hematocrit bias refers to the difference between a reference glucose concentration obtained with a standard instrument and a test glucose reading obtained by a biosensor for samples having different hematocrit levels. The difference between the reference value and the value obtained by the biosensor is due to different hematocrit levels between the specific whole blood samples.

In addition to the hematocrit effect, measurement inaccuracies can also occur when the concentration of the measurable species is not correlated with the analyte concentration. For example, when the sensor system determines the concentration of reduced mediator generated by oxidation of the analyte, any reduced mediator that is not generated by the analyte oxidation reaction will cause the sensor system to indicate that more analyte is present in the sample than is the case accurately, due to the mediator background. Thus, a "vehicle background" is a deviation introduced into a measured analyte concentration due to a measurable substance not corresponding to an intrinsic analyte concentration.

In an attempt to overcome one or more of these disadvantages, conventional biosensors have attempted a variety of techniques that not only address the mechanical design of the sensor strip, but also relate to the manner in which the measuring device applies an electrical potential to the sensor strip. For example, common methods for reducing the hematocrit effect of amperometric sensors include the use of filters, as disclosed in US5708247 and US 5951836; reversing the polarity of the applied current, as disclosed in WO 2001/57510; and by maximizing the intrinsic resistance of the sample.

Various methods of applying input signals to sensor strips, commonly referred to as pulse methods, sequence methods, or cycling methods, have been employed to address inaccuracies in the determined analyte concentration. For example, in US4897162, an input signal comprises successively applied rising and falling voltage potentials that are mixed together to give a triangular waveform. In addition, WO2004/053476, US2003/0178322 and US2003/0113933 disclose input signals comprising successively applying rising and falling voltage potentials of varying polarity.

Other common methods combine a specific electrode structure with an input signal suitable for that structure. For example, U.S. patent No.5942102 combines a special electrode structure formed by thin layer elements with a continuous pulse so that reaction products from the counter electrode reach the working electrode. This combination is used to drive the reaction until the current is constant over time, so that the mediator moving between the working electrode and the counter electrode during the potential step reaches a true steady state condition. While each of these approaches balances various advantages and disadvantages, none is ideal.

As can be seen from the above description, there is a continuing need for improved biosensors, particularly biosensors that can more accurately determine analyte concentrations in a shorter period of time. The system, apparatus and method of the present invention overcome at least one of the disadvantages of conventional systems.

Disclosure of Invention

The present invention provides a method of determining the concentration of an analyte in a sample, the method comprising the steps of: applying an input signal to a sample, the input signal comprising at least 3 duty cycles within 10 seconds, wherein each duty cycle comprises an excitation pulse and a relaxation; measuring an output signal corresponding to the measurable substance within 300 milliseconds of the application of the excitation pulse for at least one duty cycle; determining the concentration of the analyte in the sample based on the measured output signal. These duty cycles may each include excitation and relaxation of a fixed potential during which a current may be recorded. The pulse sequence may comprise a terminal read pulse, which may be applied to the sensor strip comprising the diffusion barrier. The determined analyte concentration is less biased by the vehicle background than the same or other methods where no output signal is measured within 300 milliseconds. By using instantaneous current data, the concentration of the analyte can be determined when a steady state condition is not reached during the excitation pulse of the input signal duty cycle. The measured current may be subjected to data processing for determining the analyte concentration in the sample.

A hand-held measuring device for receiving the sensor strip is provided for determining the analyte concentration in the sample. The device includes contacts, at least one display, and circuitry for establishing an electrical connection between the contacts and the display. The circuit includes a charger and a processor, wherein the processor is electrically connected to a storage medium. The storage medium includes computer readable software code that, when executed by the processor, causes the charger to execute an input signal between the contacts that includes at least 3 duty cycles within 10 seconds. Each duty cycle includes excitation and relaxation. The processor may be operable to measure at least one current value at the at least two contacts within 300 milliseconds of the charger applying the excitation. The processor may also be configured to determine an analyte in the biological fluid based on the at least one current value.

The present invention provides a biosensor system for determining the concentration of an analyte in a sample. The system comprises: a sensor strip having a sample interface adjacent to the container formed by the sensor strip, and a measurement device having a processor coupled to the sensor interface. The sensor interface is electrically connected with the sample interface, and the processor is electrically connected with the storage medium. The processor determines an output signal value from the sensor interface corresponding to the concentration of the analyte in the sample within 300 milliseconds of applying the excitation pulse to the sample interface. The excitation pulse is a portion of the input signal that includes at least 3 duty cycles within 10 seconds, each duty cycle including excitation and relaxation.

The present invention also provides a method for reducing bias due to the hematocrit effect of a determined analyte concentration in a sample, the method comprising applying to the sample an input signal comprising at least 3 duty cycles within 10 seconds. The output signal from which the analyte concentration in the sample is determined is recorded within 300 milliseconds of the application of the excitation pulse.

Drawings

The invention will be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

FIG. 1 shows an electrochemical assay for determining the presence and/or concentration of an analyte in a sample.

Fig. 2 is a graph showing an output signal generated from an input signal for gated current measurement.

FIG. 3A shows the hematocrit bias present in the analyte concentration values determined from each of the three current values measured from each of the seven pulses shown in FIG. 2.

FIG. 3B shows the hematocrit bias ranges for samples including 50, 100, and 400mg/dL glucose.

FIG. 4 shows the hematocrit bias of the first and third current values from P5 in FIG. 3A for a plurality of whole blood samples.

FIG. 5 shows a schematic of a biosensor used to determine the concentration of an analyte in a sample.

Detailed Description

In WO2007/013915 entitled "Gated Amperometer," a pulsed input signal is used to analyze an analyte in a sample. The input signal comprises alternating excitation periods and relaxation periods. The present invention relates to systems and methods for analyzing an output signal from a pulsed input signal to reduce bias due to, for example, vehicle background and hematocrit effects. By correlating the output signal values measured within the first 300ms of the excitation pulse, the accuracy and/or precision of the analysis may be improved.

FIG. 1 shows an electrochemical analysis method 100 for determining the presence and/or concentration of an analyte in a sample. In step 110, a sample is introduced into the biosensor. In step 120, a portion of the analyte in the sample undergoes a redox reaction. In step 130, electrons are selectively transferred from the analyte to the mediator. In step 140, the measurable species is electrochemically excited with the input signal. In step 150, an output signal is generated and measured. In step 160, the sample is allowed to relax, and in step 170, additional excitation pulses are input. In step 180, the presence and/or concentration of the analyte in the sample is determined from the output signal, and in step 190, the concentration is displayed, stored, etc.

In step 110, the sample is introduced into a sensor portion (e.g., a sensor strip) of the biosensor. The sensor strip includes at least one working electrode and at least one counter electrode. The electrodes may include one or more reagent layers. The working electrode may include a diffusion barrier layer integral with or separate from the reagent layer. Where the working electrode includes a separate diffusion barrier layer, the reagent layer need not be disposed on the diffusion barrier layer.

The diffusion barrier is provided with a porous space having an internal volume in which the measurable species may reside. The porosity of the diffusion barrier may be selected such that the measurable species may diffuse into the diffusion barrier while substantially excluding larger volumes of sample constituents (e.g., red blood cells). While conventional sensor strips have employed various materials to filter out red blood cells from the surface of the working electrode, the diffusion barrier provides an internal porous space to contain and isolate a portion of the measurable species from the sample. A more detailed description of the diffusion barrier can be seen in U.S. patent publication No. 2007/0246357.

In step 120 of fig. 1, a portion of the analyte present in the sample is chemically or biochemically oxidized or reduced, for example, by an oxidoreductase, due to hydration of the sample with the reagent. Upon the occurrence of an oxidation or reduction reaction, electrons can be selectively transferred between the analyte and the mediator in step 130. Thus, for example, an ionized measurable species is formed from the analyte or the mediator. It is desirable to provide an initial time delay or "incubation" for the reagent to react with the analyte. Preferably, the initial time delay may be 1 to 10 seconds. A more detailed description of the initial time delay can be seen in US patents US5620579 and US 5653863.

In step 140 of fig. 1, the input signal is used to electrochemically excite (oxidize or reduce) a measurable species, which may be the charged analyte from step 120 or the charged vehicle from step 130. The input signal may be an electrical signal (e.g., current or potential) that is pulsed or switched on and off in a set sequence. The input signal is a sequence of excitation pulses separated by relaxations. During the current measurement pulse, the potential applied during the excitation is preferably applied at a substantially constant voltage and polarity throughout its duration. This is in direct contrast to some common excitations in which the voltage changes or "swapt" through multiple voltage potentials and/or polarities during data recording.

During relaxation, the electrical signal is disconnected. Disconnection includes periods of absence of an electrical signal, preferably periods of absence of an electrical signal but substantially no amplitude. The electrical signal can be switched on and off by closing and opening an electrical circuit, respectively. Mechanical, electrical, or other methods may be employed to close and open the electrical circuit.

The input signal may have one or more pulse intervals. The pulse interval is the sum of the pulses and the relaxation that make up the duty cycle. Each pulse has an amplitude and a width. The amplitude represents the intensity of the potential, current, etc. of the electrical signal. The amplitude may be varied or substantially constant, for example during current measurement, during a pulse. The pulse width is the duration of the pulse. The pulse width of the input signal may be varied or substantially the same. Each relaxation has a relaxation width, which is the duration of the relaxation. The relaxation widths of the input signals may be varied or substantially the same.

Gating the input signal may improve the accuracy and/or precision of the analysis by adjusting the width of the excitation and relaxation of the duty cycle. While not wishing to be bound by any particular theory, this improvement in accuracy and/or precision is a result of the extraction of excited measurable species at the working electrode from the interior of the diffusion barrier. In contrast to measurable species outside of diffusion barriers that have varying diffusion rates due to red blood cells and other sample compositions, measurable species within the diffusion barrier have relatively constant diffusion rates to the conductor. For example, as described in U.S. patent publication No.2007/0246357 entitled "concentration determination in a Diffusion Barrier Layer," the pulse width may be selected to substantially limit the measurable species excitation to the Diffusion Barrier.

Preferred input signals include at least 3, 4, 6, 8 or 10 duty cycles applied during less than 30, 10 or 5 seconds. More preferably, at least 3 duty cycles are applied within 10 seconds. It is presently particularly preferred to include an input signal that is applied for at least 4 duty cycles in less than 7 seconds. Preferably, the width of each excitation pulse is independently selected from 0.1 to 2 seconds, more preferably from 0.2 to 1 second. At present, it is especially preferable that the pulse width of the input signal is independently selected from 0.3-0.8 second. Preferred pulse intervals are in the range of less than 3, 2.5 or 1.5 seconds. Currently, input signals having a pulse width of 0.3 to 0.5 seconds and a pulse interval of from 0.7 to 2 seconds are particularly preferred. The input signal may have other pulse widths and spacings.

In step 150 of FIG. 1, the biosensor generates an output signal based on the measurable substance and the input signal. The output signal (e.g., one or more current values) may be measured continuously or intermittently, or may be recorded as a function of time. The output signals may include signals that fall from the beginning, signals that increase and then fall, signals that reach steady state, and signals that are transient. Steady state current is observed when the change in current with respect to time is substantially constant (e.g., within ± 10% or ± 5%). Instead of a normal steady-state or slowly decaying current, a momentary (rapidly decaying) current value can be obtained from the pulsed input signal.

Fig. 2 is a graph showing an output signal generated from a gated current measurement input signal. Each excitation pulse, when plotted as a function of time, results in a transient decay curve in which the initial high current value decays. The input signal applied by the biosensor comprises eight pulses and seven relaxations for a total of seven duty cycles. The first duty cycle is omitted from fig. 2, showing that there is no relaxation after the eighth pulse. The pulse was applied at about 200mV, with a pulse width of about 0.4 seconds. The pulse interval of the duty cycle is about 1.4 seconds, providing a relaxation width of about 1 second. Relaxation is provided by the open circuit. Although square wave pulses are used, other waveforms suitable for the sensor system and the test sample may be used.

The biosensor intermittently measures the output signal during each pulse in fig. 2, and the three current values are recorded in the storage means. From each to eachThe output signal values are recorded at intervals of approximately 125 milliseconds (ms) from approximately 125ms after the start of each pulse. The interval between successive recordings may be the same or different. In fig. 2, three current values from the output signal are recorded and identified by the letter i, with the pulse number and the measurement number being indicated by subscripts. Therefore, the third current value measured for the fifth pulse is denoted as i_5，3。

FIG. 3A shows the hematocrit bias present in analyte concentration values determined from each of the three current values measured from each of the seven pulses shown in FIG. 2, with a larger absolute value on the Y-axis indicating a larger hematocrit error. For each pulse, the first current value indicates a minimum hematocrit deviation of the three values, and the deviation between the first and third values becomes larger with each subsequent pulse. For each subsequent pulse, a lower mean hematocrit bias over the measured current is observed; however, each additional pulse extends the analysis time period. Thus, while the current value from P8 includes little to no hematocrit error, the first current value from P5 may provide a preferred balance between hematocrit error and analysis time. It is also noteworthy that the first current value measured for P5 has about the same hematocrit error as the third current value from the following P8 for more than three seconds. These results indicate that the current values measured earlier in the pulse width include the smallest hematocrit error.

FIG. 3B shows the range of hematocrit bias for samples including 50, 100, and 400mg/dL glucose, with larger values of the range on the Y-axis indicating greater hematocrit error. As shown in fig. 3A, the first current value indicates the minimum hematocrit bias of the four current values measured during each pulse, and the bias between the first and fourth values becomes larger with each subsequent pulse. The unexpectedly low hematocrit bias of the first current values measured for each pulse was more pronounced at the higher 400mg/dL glucose concentration levels. Therefore, accuracy is improved by performing the current measurement as early as possible in the attenuation that increases as the glucose concentration of the whole blood sample increases.

FIG. 4 shows the hematocrit bias of the first and third current values from P5 of FIG. 3A for a plurality of whole blood samples including varying hematocrit and glucose contents. First current value i_5，1Shows R²Correlation is 0.18, third Current value i_5，3Shows R₂The correlation is 0.08, and is reduced by more than 50%. The higher analyte concentration accuracy from current values taken early in the decay is unexpected in direct contrast to the prior art, which achieves accuracy from measurements taken in the later steady-state portion of the decay. These results indicate that higher accuracy and/or precision can be achieved from measurements taken early in the transient portion of the rapid change in attenuation.

Preferably, the output current value from which the analyte concentration is determined is measured within less than 300ms of the application of the excitation pulse. More preferably, the output current value used to determine the analyte concentration of the sample is measured within less than 175ms from the application of the excitation pulse or within 10 to 150ms of the application of the pulse. Even more preferably, the output current value on which the concentration is determined is measured within 30 to 150ms of the application of the excitation pulse. At present, it is particularly preferred to determine the analyte concentration from the output current value measured within 60 to 150ms of the application of the excitation pulse. Preferably, the pulse from which the analyte output current value is measured to determine the concentration of analyte in the sample is applied within 11 seconds or less of the application of the initial excitation pulse, more preferably within 7 seconds or less of the application of the initial pulse.

In step 160 of fig. 1, the sample undergoes relaxation. The measurement device may break the circuit through the sensor strip, thus allowing relaxation. During the relaxation of step 160, the current present during the excitation of step 140 is substantially reduced by at least half, preferably by an order of magnitude, more preferably to zero. Preferably, the zero current condition is achieved by opening a circuit or other method known to those of ordinary skill in the art to provide substantially zero current. Preferably, no output signal is recorded during the relaxation of step 160.

During the relaxation of step 160, an ionizing agent (e.g., an oxidoreductase) may react with the analyte to produce additional measurable species without the influence of a potential. For example, a glucose biosensor that includes glucose oxidase and a ferricyanide mediator as reagents produces additional ferrocyanide (reduced mediator) corresponding to the analyte concentration of the sample without potential interference during the relaxation of step 160.

In step 170 of fig. 1, the biosensor continues to apply pulses from the input signal to the working electrode and the counter electrode for a prescribed time. The duty cycle comprising the excitation phase of step 140 and the relaxation phase of step 160 may be repeated or duty cycles having different pulse widths and/or intervals may be applied.

In step 180 of fig. 1, the biosensor analyzes the output signal values recorded within 300ms of the applied pulse to determine the analyte concentration in the sample. Other currents, times, and/or other values may also be analyzed. In step 190, the analyte concentration value may be displayed, stored, used for future reference, and/or used for additional calculations.

Fig. 5 shows a schematic diagram of a biosensor 500 for determining the concentration of an analyte in a biological fluid sample using a pulsed input signal. Biosensor 500 includes a measurement device 502 and a sensor strip 504, which may be implemented as any analytical instrument, including a desktop device, a portable or handheld device, and the like. The biosensor 500 may be used to determine analyte concentrations, including concentrations of glucose, uric acid, lactate, cholesterol, bilirubin, and the like. Although a specific structure is shown, biosensor 500 may have other structures as well, including those with additional components.

The sensor strip 504 has a base 506, the base 506 forming a reservoir 508 and a channel 510 with an opening 512. The receptacle 508 and the channel 510 may be covered with a lid having an aperture. The container 508 defines a partially enclosed space. The reservoir 508 may contain components that help retain the liquid sample, such as a water-swellable polymer or a porous polymer matrix. Reagents may be contained in the container 508 and/or the channel 510. The reagent may include one or more of an enzyme, a binder, a vehicle, and the like. The sensor strip 504 may also have a sample interface 514 disposed adjacent the container 508. The sample interface 514 may partially or completely surround the container 508. Sensor strip 504 may have other configurations.

The sample interface 514 has leads that connect to the working electrode and the counter electrode. The electrodes may be in substantially the same plane or in more than one plane. Other spacing distances between the electrodes and the cover may also be used. These electrodes may be disposed on the surface of the substrate 506 forming the container 508. The electrodes may extend or protrude into the container 508. The dielectric layer may partially cover the conductive lines and/or electrodes. The sample interface 514 may also have other electrodes and leads.

The measurement device 502 includes circuitry 516 coupled to a sensor interface 518 and a display 520. The circuit 516 includes a processor 522 coupled to a signal generator 524, an optional temperature sensor 526, and a storage medium 528.

The signal generator 524 provides an electrical input signal to the sensor interface 518 in response to the processor 522. The electrical input signal may be communicated by the sensor interface 518 to the sample interface 514 to apply the electrical input signal to the biological fluid sample. The electrical input signal may be a potential or a current, may be a constant value, a variable, or a combination thereof, for example with a DC signal offset when an AC signal is applied. The electrical input signal may be applied in the form of a single pulse, multiple pulses, a sequence or a periodic wave. The signal generator 524 may also record the output signal from the sensor interface as a generator-recorder.

An optional temperature sensor 526 determines the temperature of the sample in the container of the sensor strip 504. The sample temperature may be measured, calculated from the output signal, or assumed to be the same as or similar to the ambient temperature or the measured value of the temperature of the device constituting the biosensor system. The temperature may be measured using a thermistor, thermometer, or other temperature sensing device. Other techniques for determining the temperature of the sample may also be used.

The storage medium 528 may be a magnetic, optical, or semiconductor memory, or other storage device, etc. The storage medium 528 may be a fixed storage device, a removable storage device (e.g., a memory card, remote access, etc.).

The processor 522 employs computer readable software code and data stored in the storage medium 528 for analyte analysis and data processing. Processor 522 may initiate an analyte analysis based on the presence of sensor strip 504 at sensor interface 518, application of a sample to sensor strip 504, response to a user input, and the like. Processor 522 controls signal generator 524 to provide an electrical input signal to sensor interface 518. Processor 522 may receive the sample temperature from an optional temperature sensor 526. Processor 522 receives the output signal from sensor interface 518. The output signal is generated in response to a redox reaction of an analyte in the sample. Processor 522 measures the output signal within 300ms of the application of the excitation pulse from signal generator 524. One or more relationships are employed in processor 522 to correlate the output signal to the analyte concentration of the sample. The results of the analyte analysis may be output to display 520 and may be stored in storage medium 528.

The relationship relating the analyte concentration to the output signal may be represented graphically, mathematically, or a combination thereof. These relationships may be represented by a program sequence number (PNA) table, another look-up table, etc. stored in the storage medium 528. The instructions for performing analyte analysis may be provided by computer readable software code stored in storage medium 528. The code may be object code or any other code that describes or controls the functions described herein. One or more data processes (including determining decay rate, K-factor, ratio, etc.) may be performed on the data from the analyte analysis in processor 522.

The sensor interface 518 has contacts that connect or electrically communicate with wires in the sample interface 514 of the sensor strip 504. Sensor interface 518 communicates electrical input signals from signal generator 524 through contacts to connectors in sample interface 514. Sensor interface 518 also communicates output signals from the test sample to processor 522 and/or signal generator 524 via contacts.

The display 520 may be analog or digital. The display may be an LCD display adapted to display a digital readout.

In use, a liquid sample for analysis is transferred into the receptacle 508 by introducing liquid into the opening 512. The liquid sample flows through the channel 510, filling the container 508 while venting the previously contained air. The liquid sample chemically reacts with reagents contained in the channel 510 and/or the container 508.

Sensor strip 504 is positioned adjacent to measurement device 502. Adjacent locations include locations where sample interface 514 is in electrical and/or optical communication with sensor interface 518. Electrical communication includes transferring input and/or output signals between contacts in sensor interface 518 and wires in sample interface 514. Optical communication includes transmitting light between an optical port in sample interface 514 and a detector in sensor interface 518. Optical communication also includes transmitting light between an optical port in the sample interface 514 and a light source in the sensor interface 508.

While various embodiments of the invention have been described above, it will be apparent to those of ordinary skill in the art that other embodiments and implementations are possible within the scope of the invention. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.

Claims (56)

1. A method of determining the concentration of an analyte in a sample for non-diagnostic purposes, the method comprising the steps of:

applying an input signal to the sample, the input signal comprising at least 3 duty cycles within 10 seconds, each duty cycle comprising an excitation pulse and a relaxation;

measuring an output signal corresponding to a measurable substance within 300 milliseconds of application of said excitation pulse for at least one of said duty cycles; and

determining the concentration of the analyte in the sample from the measured output signal.

2. The method of claim 1, wherein the input signal comprises at least 4 duty cycles within 7 seconds.

3. The method of claim 1 or 2, wherein the excitation pulse has a pulse width of 0.1 to 2 seconds.

4. The method of claim 1 or 2, wherein the excitation pulse has a pulse width of 0.3 to 0.8 seconds.

5. A method according to claim 1 or 2, wherein the pulse interval of at least one of the duty cycles is less than 3 seconds.

6. The method of claim 1 or 2, wherein the excitation pulse has a pulse width of 0.3 to 0.5 seconds and the pulse interval is 0.7 to 2 seconds.

7. A method according to claim 1 or 2, wherein the output signal is measured within less than 175 milliseconds of the application of the excitation pulse of the one duty cycle.

8. A method according to claim 1 or 2, wherein the output signal is measured within 60 to 150 milliseconds of the application of the excitation pulse of the one duty cycle.

9. A method according to claim 1 or 2, wherein the duty cycle according to which the output signal is measured is applied within 11 seconds or less of the application of the initial excitation pulse to the sample.

10. A method according to claim 1 or 2, wherein the duty cycle according to which the output signal is measured is applied within 7 seconds or less of the application of the initial excitation pulse to the sample.

11. The method of claim 1 or 2, further comprising: introducing the sample onto a sensor strip and then transferring at least one electron from an analyte of the sample to a mediator in the sensor strip, wherein the input signal electrochemically excites the measurable species selected from the group consisting of the analyte, the mediator, and combinations thereof.

12. A method as claimed in claim 1 or 2, wherein the excitation pulse has a substantially constant voltage.

13. A method as claimed in claim 1 or 2, wherein the input signal comprises a square wave excitation signal.

14. The method of claim 1, wherein said method determines a smaller deviation in said analyte concentration than if the same or other method did not include said input signal for at least 3 duty cycles within 10 seconds and did not measure said output signal corresponding to said measurable species within 300 milliseconds of application of an excitation pulse for said one duty cycle.

15. The method of claim 1 or 2, further comprising recording at least one current as a function of time during application of the input signal.

16. A method according to claim 1 or 2, wherein said determining comprises at least one data processing of at least one current of said output signal.

17. The method of claim 11, further comprising:

exciting a measurable species within a diffusion barrier, wherein the diffusion barrier is included on the sensor strip and is provided with a porous space having an interior volume in which the measurable species can reside; and

substantially excluding the measurable species outside the diffusion barrier by excitation.

18. The method of claim 1 or 2, wherein the relaxation corresponds to opening a circuit.

19. The method of claim 1 or 2, wherein the relaxation is at least 0.5 seconds.

20. The method of claim 1 or 2, wherein the output signal comprises a transient decay from which the analyte concentration is determined.

21. The method of claim 1 or 2, wherein the sample is selected from the group consisting of a biological fluid, a derivative of a biological fluid, and combinations thereof.

22. The method of claim 1 or 2, wherein the measurement is performed by a portable measuring device.

23. A hand-held measuring device for determining the concentration of an analyte in a sample,

the device is adapted to receive a sensor strip, the device comprising:

a contact;

at least one display; and

a circuit that establishes electrical communication between the contact and the display, the circuit comprising:

a charger and a processor in electrical communication with each other, the processor in electrical communication with a storage medium comprising computer readable software code, which when executed by the processor causes the charger to perform an input signal between the contacts comprising at least 3 duty cycles within 10 seconds, each duty cycle comprising an excitation and a relaxation,

wherein the processor is to measure at least one current value at the at least two contacts within 300 milliseconds of the charger applying the excitation pulse, and

the processor is configured to determine an analyte concentration in the biological fluid based on the at least one electrical current value.

24. The device of claim 23, wherein the device is portable.

25. The apparatus of claim 23 or 24, wherein the charger is configured to perform the excitation pulse at a substantially constant voltage.

26. The apparatus of claim 23 or 24, wherein the processor is operative to measure the at least one current value during a transient portion of decay.

27. The device of claim 23 or 24, wherein the sample is selected from the group consisting of a biological fluid, a derivative of a biological fluid, and combinations thereof.

28. The apparatus of claim 23 or 24, wherein the processor is to measure at least one current value at the at least two contacts within 175 milliseconds of the charger applying an excitation pulse.

29. The apparatus of claim 23 or 24, wherein the input signal comprises at least 4 duty cycles within 7 seconds.

30. The apparatus of claim 23 or 24, wherein the excitation pulse has a pulse width of 0.1 to 2 seconds.

31. The apparatus of claim 23 or 24, wherein the excitation pulse has a pulse width of 0.3 to 0.8 seconds.

32. The apparatus of claim 23 or 24, wherein a pulse interval of at least one of the at least 3 duty cycles is less than 3 seconds.

33. The apparatus of claim 23 or 24, wherein the processor is configured to determine the analyte concentration in the biological fluid within 7 seconds or less of the charger performing the input signal.

34. The apparatus of claim 23 or 24, wherein the relaxation corresponds to opening a circuit.

35. A biosensor system for determining the concentration of an analyte in a sample, the system comprising:

a sensor strip having a sample interface adjacent to a container formed by the sensor strip; and

a measurement device having a processor connected to the sensor interface, the sensor interface in electrical communication with the sample interface, the processor in electrical communication with a storage medium,

wherein the processor determines an output signal value from the sensor interface corresponding to an analyte concentration in the sample within 300 milliseconds of applying an excitation pulse to the sample interface,

the excitation pulse is a portion of the input signal that includes at least 3 duty cycles within 10 seconds, each duty cycle including excitation and relaxation.

36. The system of claim 35, wherein the measurement device is portable.

37. The system of claim 35 or 36, wherein the excitation pulse has a substantially constant voltage.

38. The system of claim 35 or 36, wherein the output signal value corresponding to the concentration of the analyte in the sample is determined during a transient portion of the decay.

39. The system of claim 35 or 36, wherein the sample is selected from the group consisting of a biological fluid, a derivative of a biological fluid, and combinations thereof.

40. The system of claim 35 or 36, wherein the processor determines an output signal value from the sensor interface corresponding to an analyte concentration in the sample within 175 milliseconds of applying an excitation pulse to the sample interface.

41. The system of claim 35 or 36, wherein the input signal comprises at least 4 duty cycles within 7 seconds.

42. The system of claim 35 or 36, wherein the excitation pulse has a pulse width of 0.1 to 2 seconds.

43. The system of claim 35 or 36, wherein the excitation pulse has a pulse width of 0.3 to 0.8 seconds.

44. The system of claim 35 or 36, wherein at least one of the at least 3 duty cycles has a pulse interval of less than 3 seconds.

45. The system of claim 35 or 36, wherein the relaxation corresponds to opening a circuit.

46. A method for non-diagnostic purposes of reducing bias in the determined concentration of an analyte in a sample, the method comprising the steps of:

applying an input signal to the sample, the input signal comprising at least 3 duty cycles within 10 seconds, and each duty cycle comprising an excitation pulse and a relaxation;

measuring an output signal corresponding to a measurable substance within 300 milliseconds of application of the excitation pulse for the at least one duty cycle; and

determining the analyte concentration in the sample from the measured output signal.

47. The method of claim 46, wherein at least a portion of the bias is due to a hematocrit effect.

48. The method of claim 46 or 47, wherein the sample is selected from the group consisting of a biological fluid, a derivative of a biological fluid, and combinations thereof.

49. The method of claim 46 or 47, wherein the output signal comprises a transient decay from which the analyte concentration is determined.

50. The method of claim 46 or 47, wherein an output signal corresponding to the measurable species is measured within 175 milliseconds of the application of the excitation pulse of the at least one duty cycle.

51. A method according to claim 46 or 47, wherein the input signal comprises at least 4 duty cycles within 7 seconds.

52. The method of claim 46 or 47, wherein the excitation pulse has a pulse width of 0.1 to 2 seconds.

53. The method of claim 46 or 47, wherein the excitation pulse has a pulse width of 0.3 seconds to 0.8 seconds.

54. A method according to claim 46 or 47, wherein the pulse interval of at least one of said at least 3 duty cycles is less than 3 seconds.

55. The method of claim 46 or 47, wherein the analyte concentration in the sample is determined within 7 seconds or less of applying the input signal to the sample.

56. The method of claim 46 or 47, wherein the relaxation corresponds to opening a circuit.