JP2017009431A - Sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sensor that exhibits less reduction in sensitivity after prolonged use or storage.SOLUTION: A sensor is for electrochemically quantifying an analyte and includes a working electrode 21, a counter electrode 22, and a reagent layer 3 containing at least an enzyme that reacts with a substrate, and a mediator. Surfaces of the working electrode 21 and the counter electrode 22 are at least partially covered with a coating layer comprising the reagent layer 3 with a water soluble material.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a sensor using an electrochemical method.

  Various sensors (biosensors) using an electrochemical method are known, such as a glucose sensor such as a blood glucose level sensor.

  For example, when a specimen (blood or the like) is introduced into a cavity (a space formed by a groove formed in a spacer) of a biosensor, a component (substrate) contained in the specimen reduces the mediator via an enzyme. Here, when a predetermined voltage is applied to the electrode, the reduced mediator is reversely oxidized by an electrochemical reaction. By measuring the oxidation current generated at this time, the amount of the component of interest can be detected.

  Such a biosensor generally includes two or more electrodes including at least a working electrode and a counter electrode. After a spacer for forming a cavity is bonded on the electrode, an enzyme, It has a structure in which a reagent layer containing a mediator or the like is formed and a cover is attached.

  Heretofore, in the technical field of the present invention, it has been pointed out that the biosensor after long-term use or storage has a problem that the detection sensitivity of the electrode is lowered. Note that the current value detected by the electrode may decrease over time even at room temperature, depending on the storage time, but it is known that the current decrease becomes significant especially in a high temperature environment exceeding 30 ° C. .

  In Patent Document 1, as a cause of the current decrease, when an electrode (electrode film) is a metal film formed by a sputtering method, a gas component such as a sputter gas, a base material, or an outgas from the inner wall of the apparatus is produced. In the preservation process, a gas component is released from the metal film, thereby creating a gap in the metal film, and filling the gap with the metal component changes the physical properties of the metal film ( It is described that the surface resistance value is considered to decrease.

  For this reason, in Patent Document 1, in order to improve the long-term stability of the electrode film, the gas component existing in the electrode film is reduced by selecting a film formation condition in which the gas component is not easily taken into the electrode film. It has been proposed to suppress changes over time.

JP 2009-132138 A

  However, when the present inventors tried the same experiment as in Patent Document 1, even if the above conditions were optimized, the gas component could not be completely removed from the electrode film, and the electrode film still remains. Since pores were generated in the electrode, it was impossible to completely suppress changes in electrode characteristics (current drop) associated with storage time. In addition, it was found that the current decrease becomes remarkable especially in a high temperature environment exceeding 30 ° C.

  Therefore, in the sensor disclosed in Patent Document 1, the effect of suppressing a decrease in detection sensitivity of the electrode after long-term use or storage is not always sufficient. In particular, there is a problem in that a decrease in detection sensitivity of the electrode cannot be sufficiently suppressed under a high temperature condition exceeding 30 ° C.

  This invention is made | formed in view of the said subject, and it aims at providing the sensor which can suppress the fall of the detection sensitivity after a long-term use or a storage more than before.

[1]
A sensor for electrochemically quantifying an analyte,
With electrodes,
A sensor, wherein at least a part of a surface of the electrode is covered with a coating layer containing a water-soluble substance.
[2]
The analyte includes an object other than a substrate,
The sensor according to [1], wherein at least a part of a surface of an electrode for quantifying an object other than the substrate is covered with the coating layer.
[3]
The sensor according to [1] or [2], wherein the water-soluble substance is at least one of a hydrophilic polymer and an amphiphilic polymer.
[4]
The sensor according to [3], wherein the hydrophilic polymer is a cellulosic polymer.
[5]
The sensor according to [3] or [4], wherein the hydrophilic polymer does not have a double-bonded oxygen atom.
[6]
The sensor according to [5], wherein the hydrophilic polymer is at least one selected from the group consisting of methylcellulose, hydroxypropylmethylcellulose, and hydroxyethylmethylcellulose, hydroxypropylcellulose, and hydroxyethylmethylcellulose.
[7]
The sensor according to [3], wherein the amphiphilic polymer is at least one selected from the group consisting of polyvinyl pyrrolidone, polyethylene glycol, and polyvinyl alcohol.
[8]
The electrode was formed on the surface by sputtering, vacuum deposition, ion plating, CVD, MBE, melt transport, melt temperature drop, sol-gel, plating or coating. The sensor according to any one of [1] to [7], including an electrode film.

  ADVANTAGE OF THE INVENTION According to this invention, the sensor which can suppress the fall of the detection sensitivity after a long-term use or storage can be provided compared with the past.

3 is a graph showing a relationship between a storage period and a hematocrit measurement current in Example 1. It is a graph which shows the relationship between the storage period and hematocrit measurement current in Example 2. It is a graph which shows the relationship between the storage period in Example 3, and a hematocrit measurement electric current. 6 is a graph showing a relationship between a storage period and a hematocrit measurement current in Comparative Example 1. 1 is an exploded perspective view showing a configuration of a biosensor of Embodiment 1. FIG. 6 is a perspective view for explaining an example of a manufacturing process of the biosensor of Embodiment 1. FIG. It is another perspective view for demonstrating an example of the manufacturing process of the biosensor of Embodiment 1. FIG. It is another perspective view for demonstrating an example of the manufacturing process of the biosensor of Embodiment 1. FIG. It is another perspective view for demonstrating an example of the manufacturing process of the biosensor of Embodiment 1. FIG. It is another perspective view for demonstrating an example of the manufacturing process of the biosensor of Embodiment 1. FIG. 6 is a schematic top view for explaining the configuration of the biosensor of Embodiment 2. FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same reference numerals represent the same or corresponding parts. In addition, dimensional relationships such as length, width, thickness, and depth are changed as appropriate for clarity and simplification of the drawings, and do not represent actual dimensional relationships. Each embodiment is an exemplification, and needless to say, partial replacement or combination of configurations shown in different embodiments is possible.

[Embodiment 1]
Referring to FIG. 5, the sensor of this embodiment is a biosensor for quantifying a substrate contained in a sample solution, and includes an insulating substrate 1, an electrode, a reagent layer 3, a spacer 4, And a cover 5.

The electrode includes a working electrode 21 and a counter electrode 22 provided on one surface of the insulating substrate 1.
The reagent layer 3 is formed on a part of the surface of the electrode opposite to the insulating substrate 1 and includes at least an enzyme that reacts with a substrate and a mediator. The reagent layer 3 further contains a water-soluble substance, whereby the reagent layer 3 also serves as an electrode coating layer.

  The spacer 4 has a notch 42 for forming a cavity 41 for guiding the sample solution to the reagent layer 3 and is arranged on the electrode so that the reagent layer 3 is located inside the notch 42 (cavity 41). The

  The cover 5 is provided on the surface of the spacer 4 opposite to the insulating substrate 1 so as to cover at least the notch 42. The cover 5 has an air hole 5 a communicating with the cavity 41.

  The sensor (biosensor) of this embodiment is characterized in that at least a part of the surface of the electrode is covered with a coating layer (reagent layer) containing a water-soluble substance. In addition, it is preferable that at least a portion of the surface of the electrode exposed in the cavity 41 is covered with a coating layer (reagent layer).

  By covering (protecting) the surface of the electrode with a coating layer, the electrode surface's oxidation and impurity adhesion due to exposure to the surrounding environment are suppressed, so that the physical properties of the electrode film are stabilized, and the long-term stability of the sensor And heat resistance is improved. Therefore, in the sensor of the present embodiment, a decrease in detection sensitivity after long-term use or storage can be suppressed as compared with the conventional case.

  In addition, although the improvement effect of long-term stability by such a sensor of this embodiment is exhibited also at normal temperature, the physical property change of an electrode is suppressed especially in a high temperature environment of 30 degreeC or more, and the electric current to detect Since the decrease in value can be suppressed, the effect of improving long-term stability (heat resistance) is remarkable. Therefore, it is possible to provide a highly accurate and reliable blood glucose level sensor capable of measuring the patient's original blood glucose level.

  For example, when the electrode includes an electrode film formed on the surface thereof by a sputtering method or the like, when the surface of the electrode (electrode film) is coated with the coating layer, the water-soluble substance in the coating layer is the electrode film. A small amount of gas components contained in the pore are discharged. For this reason, the physical property change of the electrode film due to the separation of the gas component from the metal film in the storage process as described in Patent Document 1 can be suppressed. This action further stabilizes the physical properties of the electrode film and improves the long-term stability and heat resistance of the sensor. Therefore, it is possible to suppress a decrease in the detection sensitivity of the sensor after long-term use or storage. it can.

  The substance constituting the coating layer is a water-soluble substance (preferably a polymer compound), and is not particularly limited as long as the effect of the present invention is achieved, but is at least one of a hydrophilic polymer and an amphiphilic polymer. It is preferable that

  The hydrophilic polymer is preferably a cellulosic polymer. Further, the hydrophilic polymer preferably does not have a double-bonded oxygen atom (═O), and more preferably is a cellulose polymer that does not have a double-bonded oxygen atom.

  From the examination results of the present inventors, it has been found that particularly a hydrophilic polymer or an amphiphilic polymer having no double-bonded oxygen atom has a high function of protecting the electrode film. This is because when a water-soluble substance having a double-bonded oxygen atom, which is a chemically active functional group, is used, a functional group containing a double-bonded oxygen atom (for example, a carbonyl group) constitutes the electrode. This is probably because the physical properties of the electrode are changed by nucleophilic attack on the metal atom and donation of electrons.

  Examples of the cellulose polymer having no double-bonded oxygen atom include methylcellulose, hydroxypropylmethylcellulose, hydroxyethylmethylcellulose, hydroxypropylcellulose, and hydroxyethylmethylcellulose.

  The cellulosic polymer having no double-bonded oxygen atom is preferably at least one selected from the group consisting of methylcellulose, hydroxypropylmethylcellulose, and hydroxyethylmethylcellulose, hydroxypropylcellulose, and hydroxyethylmethylcellulose. .

  A hydrophilic polymer having a double-bonded oxygen atom may be used, and examples of the cellulose polymer having a double-bonded oxygen atom include carboxymethyl cellulose (CMC).

  The amphiphilic polymer is preferably at least one selected from the group consisting of polyvinyl pyrrolidone, polyethylene glycol, and polyvinyl alcohol.

  In the present embodiment, examples of the substrate (analyte) include glucose (blood glucose), lactic acid, cholesterol, alcohol, sarcosine, fructosylamine, pyruvic acid, lactic acid, and hydroxybutyric acid.

  The material of the insulating substrate 1 is not particularly limited, and examples thereof include a plastic material such as a PET (polyethylene terephthalate) film, a photosensitive material, paper, glass, ceramic, or a biodegradable material. These materials are also used as materials for the spacer 4 and the cover 5.

  The electrode provided on the insulating substrate 1 includes at least a working electrode 21 and a counter electrode 22. In addition to the working electrode 21 and the counter electrode 22, the electrode may include a reference electrode serving as a potential reference when measuring the electrode potential, and a detection electrode for detecting that the sample is supplied to the cavity 41.

  Materials for these electrodes (working electrode, counter electrode, reference electrode, detection electrode, etc.) include noble metals such as platinum, gold and palladium, carbon, copper, aluminum, nickel, titanium, ITO (Indium Tin Oxide: indium tin oxide). ), ZnO (zinc oxide) and the like.

  Examples of the enzyme include glucose oxidase, glucose dehydrogenase, alcohol oxidase, alcohol dehydrogenase, lactate oxidase, lactate dehydrogenase, cholesterol esterase, cholesterol oxidase, sarcosine oxidase, fructosylamine oxidase, pyruvate oxidase, hydroxybutyrate dehydrogenase, creatininase , Creatinase and DNA polymerase. Various biosensors can be produced by selecting these enzymes according to the substance to be detected (glucose, alcohol, lactic acid, cholesterol, sarcosine, fructosylamine, pyruvic acid, hydroxybutyric acid, etc.).

  For example, glucose oxidase or glucose dehydrogenase can be used to produce a glucose sensor that detects glucose in a blood sample, and alcohol oxidase or alcohol dehydrogenase can be used to produce an alcohol sensor that detects ethanol in a blood sample. For example, a lactic acid sensor for detecting lactic acid in a blood sample can be produced, and a total cholesterol sensor can be produced by using a mixture of cholesterol esterase and cholesterol oxidase.

  The mediator is a compound (electron carrier) that mediates electron transfer between the working electrode 21 and the counter electrode 22, and is preferably a substance that itself performs a redox reaction. As the mediator, for example, potassium ferricyanide, ferrocene, ferrocene derivatives, benzoquinone, quinone derivatives, osmium complexes, ruthenium complexes and the like can be used.

  The reagent layer 3 may contain a hydrophilic polymer other than the water-soluble substance for the above coating. Such a hydrophilic polymer has an effect of easily immobilizing the reagent layer 3 on the surface of the electrode or an effect of filtering impurities (such as blood cells in the blood) in the sample solution. In addition, when only these water-soluble substances exhibit these effects, it is not particularly necessary to add a hydrophilic polymer other than the water-soluble substance.

  Further, the reagent layer 3 may contain a hydrophilizing agent for promoting the introduction of the specimen. Examples of the hydrophilizing agent include surfactants such as Triton X100, Tween 20, sodium bis (2-ethylhexyl) sulfosuccinate, and phospholipids such as lecithin.

  The material of the cover 5 is preferably an insulating material. For example, a plastic such as a PET film, a photosensitive material, paper, glass, ceramic, or a biodegradable material can be used. The cover 5 preferably has an air hole 5 a communicating with the cavity 41 formed by the spacer 4. This is because the sample is sucked toward the air hole 5a by the capillary phenomenon, so that the sample can be easily introduced into the cavity 41.

(Biosensor manufacturing method)
An example of the biosensor manufacturing method of the present embodiment will be described with reference to FIGS. FIG. 5 is an exploded perspective view showing the configuration of the biosensor of this embodiment. 6-10 is a figure for demonstrating an example of the manufacturing process of the biosensor of this embodiment, Comprising: Each shows a different process. In this embodiment, a plurality of biosensors can be manufactured simultaneously.

  First, referring to FIG. 6, electrodes (working electrode 21 and counter electrode 22 for quantifying a substrate) are formed on each of a plurality of insulating substrates 1. Specifically, a conductive layer is formed on one surface of the insulating substrate 1 by a sputtering method or the like, and a pattern is formed on the formed conductive layer by laser processing, photolithography, or the like, whereby an electrode (electrode film) is formed. Form. In addition to the working electrode 21 and the counter electrode 22, the above-described reference electrode, detection electrode, and the like may be formed. Further, the electrode and the surface of the insulating substrate 1 may be subjected to plasma treatment.

  The electrode film may be, for example, sputtering, vacuum deposition, ion plating, CVD (chemical vapor deposition), MBE (molecular beam epitaxy), melt transport, melt temperature drop, sol-gel, plating It can be formed using a method, a coating method, screen printing or the like.

  The electrode is preferably formed by sputtering, vacuum evaporation, ion plating, CVD, or MBE. In these methods, as in the sputtering method, the gas component is taken into the metal film during the manufacturing process, and the gas component is detached from the metal film during the storage process, which may cause a pore in the metal film. is there.

  Therefore, in the present embodiment, when the surface of the electrode film is covered with the coating layer, the water-soluble substance in the coating layer enters the pores of the electrode film, and a trace amount of gas components that are inherent in the pores are discharged. Is done. Changes in physical properties of the electrode film due to the separation of the gas component from the metal film during the storage process can be suppressed. By such an action, the physical properties of the electrode film are further stabilized, and a decrease in detection sensitivity of the sensor can be suppressed as compared with the conventional case.

  In another embodiment, the electrode is preferably formed by a melt transport method, a melt temperature drop method, a sol-gel method, a plating method or a coating method. As for electrode films formed by these liquid phase growth methods, gas components such as nitrogen and oxygen in the atmosphere can be contained in the electrode film in the manufacturing process. The same effect as the effect is produced.

  Although the thickness of an electrode film is not specifically limited, For example, it is 5-500 nm. Within such a thickness range, characteristic changes are likely to occur particularly in the electrode film formed by the above-described process, and thus the effect of the present invention is remarkable.

  Next, referring to FIG. 7, a part of the electrodes (working electrode 21 and counter electrode 22) on the side opposite to insulating substrate 1, and the surface on the electrode side in a region where the electrode of insulating substrate 1 is not formed A spacer 4 having a notch 42 is bonded to a part of the spacer.

  Next, referring to FIG. 8, a reagent solution is dropped onto the electrode (working electrode 21 and counter electrode 22) opposite to the insulating substrate 1 (inside the notch 42), and the reagent solution is dried to dry the reagent layer. 3 is formed. In addition, for example, the liquid containing the water-soluble substance constituting the coating layer, the enzyme liquid, and the mediator liquid may be dropped in this order and then dried to form the reagent layer 3. At least the enzyme, mediator, and water-soluble substance may be added. The reagent layer 3 may be formed by dripping the liquid (mixed liquid) to be contained and then drying them.

  Next, referring to FIG. 9, the cover 5 having the air holes 5 a is laminated on the spacer 4 so as to cover at least the notch 42, whereby the cavity for guiding the sample liquid to the reagent layer 3. 41 is formed. The air hole 5 a is provided on the opposite side of the opening of the cavity 41 so as to communicate with the inside of the cavity 41.

  Next, the biosensor having the cavity 41 is obtained by dividing the biosensor assembly substrate formed by the above steps (FIGS. 10 and 5).

(How to use biosensor)
The biosensor (biochip) of the present invention is used by being mounted on a measuring instrument. In other words, a sample (blood or the like) is supplied to the cavity 41 of the biosensor mounted on the measuring instrument, and a reducing substance is generated by a reaction between a substance to be measured (such as glucose) in the sample, an enzyme, and a mediator. A voltage is applied between the working electrode 21 and the counter electrode 22 by a measuring device electrically connected to the working electrode 21 and the counter electrode 22 of the biosensor, and an oxidation current obtained by oxidizing this reducing substance is obtained. By measuring, the measurement target substance contained in the sample is quantified.

  Hereinafter, an example of a method for using the biosensor of the present invention will be described. First, blood is brought into contact with the distal end portion (inlet 41c) of the cavity 41, and the blood is introduced into the cavity 41 using capillary action. Then, a voltage is applied between the working electrode 21 and the counter electrode 22, and the current value is measured at a constant timing. The applied voltage is, for example, 0.3V. When blood is introduced into the cavity 41, the analyte in the blood reduces the mediator via the enzyme. The current that flows when a voltage is applied between the working electrode 21 and the counter electrode 22 has a correlation with the reductant concentration of the mediator, that is, the analyte concentration.

  Next, the current value after a certain time has elapsed from the voltage application is measured. For example, the current value after 3 to 5 seconds is measured. Using this current value, the concentration of the analyte can be determined from a calibration curve obtained in advance.

  In the present embodiment, an example of a biosensor for quantifying a substrate (analyte) contained in a sample solution using an enzyme reaction has been described. However, the sensor of the present invention uses an electrochemical method. The sensor is not limited to such a biosensor. Examples of sensors other than biosensors include sensors that directly measure only the blood cell count (hematocrit value) in blood using an electrochemical method.

[Embodiment 2]
Referring to FIG. 11, the biosensor of this embodiment measures the amount of blood cells (hematocrit) contained in a sample solution (blood etc.) in addition to the glucose measurement electrode (working electrode 21 and counter electrode 22). Electrode (working electrode 23 and counter electrode 24). At least a part of the surface of the electrode for measuring hematocrit (a part of the electrode surface exposed at least in the cavity 41) is covered with a coating layer containing a water-soluble substance. The biosensor of the present embodiment is different from the first embodiment in this respect, but the other points are the same as in the first embodiment.

  As in the biosensor of this embodiment, measurement of an object other than a substrate (such as glucose) (for example, measurement of blood cell volume (hematocrit), detection of sensor chip insertion into a measuring machine, detection of sample introduction into the sensor chip If the surface of electrodes (working electrode, counter electrode, etc.) used for measurement of ambient environment temperature, etc. is coated with a coating layer containing a water-soluble substance, the long-term stability and heat resistance of these electrodes are improved, and the substrate concentration measurement The accuracy of measurement other than that can be improved.

  The measurement of an object other than a substrate as described above is often performed for the purpose of increasing the measurement accuracy of the quantitative value of the substrate such as correcting the quantitative value of the substrate. As a result, the measurement accuracy of the substrate can be improved.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

[Example 1]
Basically, a biosensor having the configuration shown in FIG. 11 described in the second embodiment was manufactured. Gold was used as the material of the electrode, and a metal film made of gold was formed by sputtering, and this was patterned to produce a glucose measurement electrode (electrode film) and a hematocrit measurement electrode (electrode film). .

  Moreover, the coating layer which consists of CMC was formed by dripping CMC liquid on the surface of the electrode for hematocrit measurement, and drying the CMC liquid. As CMC, sodium carboxymethyl cellulose (trade name: CARBOXYMETHYLCELLULOSE SODIUM, manufactured by Sigma-Aldrich) was used.

  A carboxymethyl cellulose (CMC) solution, an enzyme solution, and a mediator solution were dropped in this order on the glucose measurement electrode, and then dried. A mixed solution of glucose dehydrogenase and methylcellulose was used as the enzyme solution, and a mixed solution of potassium ferricyanide and hydroxypropylmethylcellulose was used as the mediator solution. The material of the insulating substrate 1 and the spacer is polyethylene terephthalate.

[Examples 2 and 3]
In place of the CMC solution used in Example 1, a methylcellulose solution was used in Example 2, and a polyvinylpyrrolidone (PVP) solution was used in Example 3. A biosensor was fabricated. In Example 2, Metrols SM400 (trade name Metroles SM400, manufactured by Shin-Etsu Chemical Co., Ltd.) is used as methylcellulose, and in Example 3, polyvinyl pyrrolidone (trade names: polyvinyl pyrrolidone, Wako Pure Chemical Industries, Ltd. ( Used).

[Comparative Example 1]
The biosensors of Examples 2 and 3 were produced in the same manner as in Example 1 except that the CMC solution used in Example 1 of the reagent layer was not dropped.

[Test Example 1]
Prepare a mixed solution of potassium ferricyanide and potassium ferrocyanide to be used as a mediator so that the current value obtained at 100 mg / dL, which is a blood glucose level of a healthy subject, is prepared as a sample solution for measuring a hematocrit value. For simplicity, a hematocrit value was prepared as zero.

  This sample solution is supplied into the cavity of the biosensor manufactured in Examples 1 to 3 and Comparative Example 1 above, and a voltage of 1.8 V is applied between the working electrode and the counter electrode of the hematocrit measurement electrode. The value of the current flowing through the hematocrit measurement electrode (hematocrit measurement current) was measured. Measurements were made for 10 biosensors stored at 30 ° C. or 50 ° C. each immediately before the start of storage (initial), 1 month, 2 months, 3 months, 4 months, 5 months and 6 The measurement was carried out after one month, and the average value of 10 measurements at each measurement was taken as the measurement result.

  Measurement results when using each of the biosensors produced in Examples 1 to 3 and Comparative Example 1 are shown in FIGS. 1 to 4 (FIG. 1 is Example 1, FIG. 2 is Example 2, and FIG. 3 corresponds to Example 3, and FIG. 4 corresponds to Comparative Example 1.)

  In the result of Comparative Example 1 (sensor without a coating layer) shown in FIG. 4, the current value decreases with time even at 30 ° C., and the current value decreases in a short time when stored at a high temperature (50 ° C.). did. From this, it can be said that even if a chemically stable gold electrode is used, a decrease in the detected current value cannot be sufficiently suppressed.

  Next, from the results of Example 1 (coating layer made of CMC) shown in FIG. 1, the rate of decrease in the current value in Example 1 is slower than that in Comparative Example 1, and the current value decreases with time. It can be seen that is suppressed.

  In Example 1, since the electrode for measuring hematocrit is covered with the coating layer, the electrode deterioration phenomenon such as contamination of the electrode surface or oxidation of the electrode surface due to exposure to air occurs. It is thought that it was suppressed.

  In the coating layer formation process, water-soluble substances enter the pores of the electrode film formed by the sputtering method, and gas components (sputtering gas, etc.) contained in the pores are discharged, so that the sensor storage process In this case, since the phenomenon that the gas component is gradually detached from the metal film is suppressed, it is considered that the physical property change of the electrode film could be suppressed.

  Since the coating layer is formed of a water-soluble substance, it is considered that the water-soluble substance was dissolved in the sample solution at the time of measurement, and the current value could be measured without hindering the detection of the current value by the electrode.

  However, in Example 1, the current value decreased with time although the rate of decrease in the current value slowed down. This is because CMC has a double bond between oxygen and carbon of a carboxyl group (carbonyl group) capable of performing a nucleophilic attack (double bonded oxygen atom), and the carboxyl group is ionized. It is considered that this double bonded oxygen atom causes a nucleophilic attack on the electrode and acts to change the surface state of the electrode.

  Next, in the result of Example 2 (coating layer made of methylcellulose) shown in FIG. 2 and the result of Example 3 (coating layer made of PVP) shown in FIG. 3, storage at 30 ° C. and storage at 50 ° C. In either case, the current value did not decrease after 6 months.

  As described above, Example 2 has excellent long-term stability and heat resistance compared to Example 1 as a material for the coating layer as a hydrophilic polymer having no double-bonded oxygen atoms. This is considered to be because the change in the surface state of the electrode due to the double-bonded oxygen atoms was not caused by using methylcellulose as described above. Therefore, in Example 2, the long-term stability of the sensor is not inhibited without inhibiting the effect of suppressing the deterioration phenomenon of the electrode as in Example 1 and the effect of suppressing the physical property change of the electrode film formed by the sputtering method. It is thought that the heat resistance was improved.

  Further, Example 3 has excellent long-term stability and heat resistance compared to Example 1 because PVP, which is an amphiphilic polymer, is used as a material for the coating layer. Although it has a bonded oxygen atom, it is an amphiphilic polymer, the proportion of the hydrophobic group in the monomer is large, and the double bonded oxygen atom is covered by the hydrophobic group covering the double bonded oxygen atom This is considered to be because the change in the surface state of the electrode due to the double-bonded oxygen atoms no longer occurs. Therefore, in Example 3, the long-term stability of the sensor is prevented without inhibiting the effect of suppressing the electrode deterioration phenomenon similar to Example 1 and the effect of suppressing the physical property change of the electrode film formed by the sputtering method. It is thought that the heat resistance was improved.

  DESCRIPTION OF SYMBOLS 1 Insulating substrate, 21 Working electrode, 22 Counter electrode, 3 Reagent layer, 4 Spacer, 41 Cavity, 41c Inlet, 42 Notch part, 5 Cover, 5a Air hole, 6 Sample liquid.

Claims (8)

A sensor for electrochemically quantifying an analyte,
With electrodes,
A sensor, wherein at least a part of a surface of the electrode is covered with a coating layer containing a water-soluble substance. The analyte includes an object other than a substrate,
The sensor according to claim 1, wherein at least a part of a surface of an electrode for quantifying an object other than the substrate is covered with the coating layer.   The sensor according to claim 1, wherein the water-soluble substance is at least one of a hydrophilic polymer and an amphiphilic polymer.   The sensor according to claim 3, wherein the hydrophilic polymer is a cellulosic polymer.   The sensor according to claim 3 or 4, wherein the hydrophilic polymer does not have a double-bonded oxygen atom.   The sensor according to claim 5, wherein the hydrophilic polymer is at least one selected from the group consisting of methylcellulose, hydroxypropylmethylcellulose, and hydroxyethylmethylcellulose, hydroxypropylcellulose, and hydroxyethylmethylcellulose.   The sensor according to claim 3, wherein the amphiphilic polymer is at least one selected from the group consisting of polyvinyl pyrrolidone, polyethylene glycol, and polyvinyl alcohol.   The electrode was formed on the surface by sputtering, vacuum deposition, ion plating, CVD, MBE, melt transport, melt temperature drop, sol-gel, plating or coating. The sensor according to any one of claims 1 to 7, comprising an electrode film.

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