JP2019158650A - Transistor type enzyme sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To use an organic transistor which can be formed on a thin and flexible substrate by printing and is excellent in mounting on a body, and an electron transfer mediator undergoes a reversible oxidation or reduction reaction, which is suitable for monitoring a biological reaction. Provided is a transistor type enzyme sensor that detects a biological substance by a voltage change of an electrode by an enzyme reaction. SOLUTION: The reference electrode 4 and the working electrode 2 and the organic semiconductor layer 10 are provided, and the reference electrode and the working electrode are in contact with a measurement solution 3 containing an oxidation-reducing substance and / or an enzyme, and a specific substance in the measurement solution is brought into contact with the measurement solution 3. When detecting with an electrode by an enzymatic reaction, an external resistance 5 is provided between the reference electrode and the working electrode. [Selection diagram] Fig. 1

Description

  The present invention relates to a transistor-type enzyme sensor, and more particularly to a transistor-type enzyme sensor suitable for monitoring a biological reaction since it shows a reversible response when a biological substance is detected by an electrode by an enzyme reaction.

  Biosensors using bio-derived materials as elements have been applied to the measurement of the concentration of specific substances in biological fluids (blood, urine, tears, saliva, sweat, etc.) that contain a lot of contaminants, taking advantage of their high selectivity. It was. An enzyme sensor, which is one of biosensors, is a sensor that generates a product capable of being detected by an electrode by an enzymatic reaction, and detects the product as an electric current or a voltage signal from the electrode. For example, a glucose sensor used for blood glucose level measurement detects, with an electrode, oxygen or a redox substance that has been reduced in association with an oxidation reaction of glucose by the enzyme glucose oxidase, or generated hydrogen peroxide.

  By the way, the transistor-type enzyme sensor has a configuration in which a current between the source electrode and the drain electrode is controlled by applying a gate voltage through a measurement solution in which a reference electrode and a working electrode that reacts with an enzyme are immersed. ing. Therefore, when the voltage generated at the working electrode changes as the enzyme reaction proceeds, the gate voltage applied to the transistor changes. At this time, a change in the threshold voltage of the transistor or a change in current between the source electrode and the drain electrode is measured to detect a measurement target.

  For example, Patent Document 1 discloses a transistor-type enzyme sensor using the oxidase shown in FIG. The transistor used here can be constituted by a known transistor structure, and may be an inorganic transistor or an organic transistor. A redox substance called an electron transfer mediator is oxidized or reduced in accordance with the reaction between the enzyme and the biological substance, and the voltage change at the working electrode according to the Nernst equation is detected by the transistor.

Here, in the transistor-type enzyme sensor, when the electron transfer mediator undergoes reversible oxidation or reduction reaction, the voltage of the working electrode shows a change corresponding to the reversible reaction, so that the biological reaction can be monitored.
Patent Documents 2 to 4 and Non-Patent Document 1 disclose methods for causing reversible oxidation or reduction reaction of electron transfer mediators.

JP 2015-187600 A Japanese Patent Laying-Open No. 2015-187593 JP-A-64-021347 JP 2007-255906 A

ACS Sens. 2018, 3, 44-53.

  In Patent Document 1, when an organic transistor is used as a transistor-type enzyme sensor, a steady reaction between the electron transfer mediator and the working electrode does not proceed due to the high resistance of the transistor, and the stationary reaction is caused between the reference electrode and the working electrode. Since no current is generated, oxidized or reduced mediator accumulates irreversibly. Here, when an inorganic transistor is used for the transistor-type enzyme sensor, it is formed on a hard substrate, and thus there is a problem that is inconvenient for wearing on the body. Thus, in order to monitor a biological reaction with a transistor-type enzyme sensor using an organic transistor, there is a problem of irreversibility of the reaction between the electron transfer mediator and the working electrode. For this reason, it is not possible to monitor changes over time in biological reactions.

  Patent Document 2 discloses a method of adding an oxidizing or reducing agent to a measurement solution in order to make the reaction of the electron transfer mediator reversible, but a sensor that requires an additive is used when the measurement solution is a biological fluid. It is difficult to add, and it is necessary to add a stable additive.

  Patent Document 3 discloses a sensor in which an enzyme is mounted on a pH sensor that exhibits a reversible response (detects a pH change associated with an enzyme reaction), but sensitivity is insufficient in a biological fluid having a pH buffering ability.

  Patent Document 4 proposes a method of electrochemically regenerating an electron transfer mediator by applying a voltage, but it is difficult to efficiently regenerate all the redox substances electrochemically, and after voltage release Quantitativeness is a problem because the potential drifts due to reaction with dissolved oxygen.

  Non-Patent Document 1 discloses an enzyme battery type sensor that uses an electromotive force generated by an enzyme reaction as a sensor output. Short-circuiting the anode and cathode with a resistance induces a redox cycle of a redox substance or enzyme. However, it is not a sensor that detects a change in the voltage of the working electrode accompanying the progress of the enzyme reaction as a change in the threshold voltage of the transistor or a change in the current between the source electrode and the drain electrode.

  The object of the present invention is to solve the above-mentioned problems, use an organic transistor excellent in wearing on the body because it can be formed on a thin and flexible substrate, and the electron transfer mediator performs reversible oxidation or reduction reaction. A transistor-type enzyme sensor suitable for monitoring a biological reaction and detecting a biological substance by a voltage change of an electrode by an enzyme reaction is provided.

  The present invention relates to a transistor-type enzyme sensor, which is a reference electrode in contact with a measurement solution containing a redox substance and / or an enzyme, a working electrode that reacts with the redox substance and / or enzyme of the measurement solution, a reference electrode, and an action An external resistance provided between the electrode, a gate electrode for inputting a change in voltage of the reaction electrode, an organic transistor having a semiconductor layer having an organic semiconductor layer, a source electrode, and a drain electrode, and the source electrode and the drain electrode It is characterized by detecting a change in current between the two.

  In this transistor type enzyme sensor, using an organic transistor, the change in the voltage of the working electrode as the enzyme reaction proceeds is changed as the change in the threshold voltage of the transistor or the change in the current between the source electrode and the drain electrode. Since the detection is performed, it is possible to amplify a weak voltage change and realize a highly sensitive detection.

  Furthermore, in this transistor-type enzyme sensor, by providing an external resistance between the reference electrode and the working electrode, spontaneous oxidation of the electron transfer mediator based on the difference in standard redox potential between the reference electrode and the working electrode is achieved. Alternatively, a reduction reaction is promoted, a steady current is generated between the reference electrode and the working electrode, and the reaction of the working electrode is made reversible, so that changes in biological reactions over time can be monitored.

The present invention is a transistor-type enzyme sensor, wherein an external capacitor is further provided between the reference electrode and the working electrode.
This transistor-type enzyme sensor uses the basic property that an external capacitor is further provided between the reference electrode and the working electrode, so that the DC current of the capacitor does not pass but the higher frequency AC current is easier to pass. Further, by removing noise generated between the reference electrode and the working electrode, it is possible to realize detection with higher accuracy.
The present invention is a transistor-type enzyme sensor, wherein a working electrode is formed integrally with a gate electrode.
In this transistor type enzyme sensor, the working electrode is formed integrally with the gate electrode, so that an extended gate electrode structure is formed, and only the working electrode is immersed in the measurement solution, which is preferable.

The present invention is a transistor-type enzyme sensor, wherein the redox material is Prussian blue.
In this transistor-type enzyme sensor, it is preferable that the redox substance is Prussian blue because Prussian blue can be selectively oxidized while avoiding oxidation of impurities because of its base standard redox potential.
The present invention is a transistor-type enzyme sensor, wherein the reference electrode is formed of silver (Ag) / silver chloride (AgCl).
In this transistor-type enzyme sensor, the reference electrode has a standard oxidation-reduction potential that is lower than that of Prussian blue, and exhibits a reversible oxidation-reduction reaction at the interface with the solution (Ag) / silver chloride (AgCl). ) Is preferable because a spontaneous reduction reaction of oxidized Prussian blue can be induced.

  As described above, in the transistor-type enzyme sensor according to the present invention, even in the case of a high-resistance organic transistor, the spontaneous reversal of the electron transfer mediator using the difference in standard redox potential between the reference electrode and the working electrode Since the reaction can be induced, a steady current is generated between the reference electrode and the working electrode, and a change with time of the biological reaction can be monitored. In addition, the organic transistor can be formed on a thin and flexible substrate by printing, so it is easy to wear on the body, and it is very small and can be placed near the working electrode. Can measure.

Sectional drawing for demonstrating the structure of Example 1 of the transistor-type enzyme sensor concerning this invention. Sectional drawing for demonstrating the other structure of Example 1 of the transistor-type enzyme sensor concerning this invention. Sectional drawing for demonstrating the other structure of Example 1 of the transistor-type enzyme sensor concerning this invention. Sectional drawing for demonstrating the other structure of Example 1 of the transistor-type enzyme sensor concerning this invention. Sectional drawing for demonstrating the other structure of Example 1 of the transistor-type enzyme sensor concerning this invention. The figure which shows the time change of the voltage applied to the gate electrode of the transistor-type enzyme sensor of Example 1. FIG. The figure which shows the time change of the voltage applied to the gate electrode of the conventional transistor-type enzyme sensor as a comparative example. Sectional drawing for demonstrating the structure of Example 2 of the transistor-type enzyme sensor concerning this invention. The figure which compares and shows the time change of the voltage applied to the gate electrode of the transistor type enzyme sensor of Example 2 and Example 1. FIG. Sectional drawing for demonstrating the structure of the conventional transistor-type enzyme sensor

  Embodiments of the present invention will be described below. A transistor-type enzyme sensor according to the present invention includes a reference electrode in contact with a measurement solution containing a redox substance and / or an enzyme, a working electrode that reacts with the redox substance and / or enzyme in the measurement solution, a reference electrode, and a working electrode. And an organic transistor having a semiconductor layer having an organic semiconductor layer, a source electrode, and a drain electrode, and an external resistance provided between the gate electrode for inputting a change in voltage of the reaction electrode, and an organic transistor having a source electrode and a drain electrode. Detect the change in current between.

  FIG. 1 illustrates a basic configuration of a transistor-type enzyme sensor according to the present invention. A working electrode 2 is formed on the surface of the substrate 1, the working electrode 2 is in contact with the measurement solution 3, and a reference electrode 4 is provided in contact with the measurement solution 3. The working electrode 2 and the reference electrode 4 are conducted through an external resistor 5 and the working electrode 2 is connected to the gate electrode 6 of the organic transistor. An organic transistor is formed by forming a gate insulating film 7 on the gate electrode 6, then a source electrode 8 and a drain electrode 9, and finally an organic semiconductor layer 10. A protective layer 11 is formed as necessary.

  The reference electrode 4 is connected to a reference potential point (ground), and a gate voltage Vg is applied to the gate electrode 6 to which the working electrode 2 is connected via the measurement solution 3. When the potential of the working electrode 2 changes as the enzyme reaction proceeds, the voltage that is effectively applied to the gate electrode 6 changes. The source electrode 8 is connected to a reference potential point (ground), and the operating voltage Vsd is supplied to the drain electrode 9. Thereby, a change in current between the source electrode 8 and the drain electrode 9 with respect to the voltage Vg supplied to the gate electrode 6 of the transistor can be detected by increasing the dynamic range according to the operating voltage Vsd. It becomes possible.

As a material of the substrate 1, for example, a resin such as polyethylene naphthalate, polyethylene terephthalate, polyethylene, polyimide, polyparaxylylene (Parylene (registered trademark)), paper, or the like can be used.
As a material of the gate electrode 6, for example, aluminum, silver, gold, copper, platinum, titanium, indium tin oxide (ITO), poly (3,4-ethylenedioxythiophene) polystyrene sulfate (PEDOT: PSS), or the like can be used. .

Examples of the constituent material of the gate insulating film 7 include silica, alumina, self-assembled monolayer (SAM), polystyrene, polyvinylphenol, polyvinyl alcohol, polymethyl methacrylate, polydimethylsiloxane, polysilsesquioxane, polytetra Fluoroethylene (Teflon (registered trademark) AF), Cytop (registered trademark), or the like can be used.
As a material of the source electrode 8 and the drain electrode 9, a conductive polymer such as aluminum, silver, gold, copper, platinum, titanium, ITO, PEDOT: PSS, or the like can be used.

As a constituent material of the organic semiconductor 10, in the case of P type, pentacene, dinaphthothienothiophene, benzothienobenzothiophene (Cn-BTBT), TIPS pentacene, TES-ADT, rubrene, P3HT, PBTT, etc. can be used. In the case of N type, fullerene or the like can be used.
As a constituent material of the protective layer 11, polytetrafluoroethylene (Teflon (registered trademark) AF), Cytop (registered trademark), polyparaxylylene (parylene (registered trademark)), or the like can be used.

The transistor manufacturing method may be a dry process such as a vapor deposition method or a sputtering method, or may be applied by spin coating, bar coating, spray coating, etc., screen printing, gravure offset printing, letterpress reverse printing, inkjet printing, or other printing machines. Good. According to printing, it can manufacture more efficiently and at low cost.
Although the gate electrode 6 and the working electrode 2 show a configuration of an extension gate that is manufactured integrally, the gate electrode 6 and the working electrode 2 may be manufactured separately and connected to each other. When not integrally formed, the material of the working electrode 2 is not limited. For example, aluminum, silver, gold, copper, platinum, carbon, titanium, ITO, PEDOT: PSS or the like can be arbitrarily selected and used. .

Examples of the redox substance 14 include Prussian blue, potassium ferrocyanide, potassium ferricyanide, ferrocene, ferrocene derivatives, quinones, osmium complexes, ruthenium complexes, phenothiazine derivatives, phenazine methosulphate derivatives, p-aminophenol, meldra blue, 2 1,6-dichlorophenolindophenol, oxidized nicotinamide adenine dinucleotide (NAD +), oxidized nicotinamide adenine dinucleotide phosphate (NADP +), and the like can be used alone or in combination. Alternatively, as shown in FIG. 2, a redox substance possessed at the active center of the enzyme 13 itself may directly react with the working electrode 2.
As the reference electrode 4, when the redox substance 14 is oxidized in the course of the enzyme reaction, an electrode having a standard redox potential lower than that of the redox substance 14 can be used. For example, a silver / silver chloride electrode can be used for Prussian blue. On the other hand, when the redox substance 14 is reduced during the enzymatic reaction, an electrode having a standard redox potential nobler than that of the redox substance 14 can be used. These redox substances 14 can be selected from the above-described redox substances 14 in any combination.

The enzyme 13 and the redox substance 14 may be dissolved in the measurement solution 3 as shown in FIGS. 1 and 2, or may be fixed on the working electrode 2 as shown in FIGS. The enzyme 13 and the redox substance 14 may be fixed in layers on the working electrode 2 (FIG. 3), or may be fixed as the mixed layers 13 and 14 (FIG. 4).
The structure of the transistor is not limited to the bottom gate structure shown in FIG. 1, and a top gate structure shown in FIG. 5 can also be used. In this case, the gate electrode 6 and the working electrode 2 are the same electrode. The structure of the surface of the gate electrode 6 can be the same as that shown in FIGS.
EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example, this invention is not restrict | limited by the following Example.

  FIG. 1 is a cross-sectional view for explaining a first embodiment of a transistor-type enzyme sensor according to the present invention. FIG. 2 is a cross-sectional view for explaining a first other configuration example of the transistor-type enzyme sensor according to the present invention. First, the configuration will be described in detail, but repeated description of the configuration common to FIGS. 1 and 2 is omitted.

  First, the transistor-type enzyme sensor shown in FIG. 1 will be described. This transistor type enzyme sensor is composed of a transistor part and an extension gate which is a detection part.

  Gold (thickness: 50 nm) is vapor-deposited on a PEN film (thickness 125 μm, Teonex, manufactured by Teijin Ltd.) on a substrate 1 through a metal mask (manufactured by Tokyo Process Service Co., Ltd.) using a vapor deposition device (produced by Cryoback). By doing so, the pattern of the working electrode 2 was produced. A PB electrode film was formed on the working electrode 2 by applying carbon containing Prussian blue (PB) (C20704424P2, manufactured by Gwent) and baking at 60 ° C. for 30 minutes. Except for the PB electrode film, Teflon (registered trademark, 5 wt%, AF1600, manufactured by Mitsui DuPont Fluorochemical Co., Ltd.) was applied and baked at 60 ° C. for 30 minutes to obtain an insulating film. A phosphate buffer solution (pH 7.4) containing 1.4 μL of 10 unit / μL glucose oxidase (manufactured by Wako Pure Chemical Industries, Ltd.) and a hydrochloric acid solution (pH 5.) containing 10 μL of 0.1 wt% chitosan (manufactured by Sigma Aldrich). 4, 0.1 wt%) was mixed, and the total amount of the mixed solution was dropped onto the surface of the PB electrode film and dried at 30 ° C. for 1 hour to obtain an enzyme-modified electrode.

In this transistor-type enzyme sensor, it is preferable that Prussian blue is selectively oxidized even in the presence of impurities when the redox material is Prussian blue.
The reference electrode 4 was formed of silver (Ag) / silver chloride (AgCl) (manufactured by BAS). In this transistor-type enzyme sensor, the reference electrode 4 is formed of silver (Ag) / silver chloride (AgCl) having a standard oxidation-reduction potential that is lower than that of Prussian blue, so that the working electrode can be formed with an external resistance. This is preferable because the Prussian blue reduction reaction proceeds spontaneously when the reference electrodes are short-circuited.

The structure of the source electrode 8 and the drain electrode 9 adopts a bottom gate contact structure. The transistor part can be manufactured by the following processes, for example.
A gate electrode 6 (Al, 30 nm) was formed on the substrate 1, and an AlOx film was formed on the surface by reactive ion etching. The substrate 1 was immersed in a tetradecylphosphonic acid solution to form a gate insulating film 7. Next, a pattern of source / drain electrodes 8 and 9 (Al, 30 nm) was formed. Thereafter, a liquid repellent bank (AF1600, manufactured by Mitsui DuPont Fluorochemical Co., Ltd.) was formed using a dispenser device, and an organic semiconductor layer 10 was formed using a semiconductor solution (pBTTT-C16, Merck KGaA) by a drop casting method. A protective layer 11 (CTL-809M, manufactured by AGC Asahi Glass Co., Ltd.) was spin-coated on the substrate 1 to produce a transistor portion. The field effect organic transistor has a configuration in which a working electrode 2 is formed on the extended gate electrode and an Ag / AgCl electrode is formed on the reference electrode 4.

  The transistor-type enzyme sensor shown in FIG. 2 differs from the transistor-type enzyme sensor shown in FIG. 1 on the surface of the working electrode 2, and the enzyme 13 reacts directly with the working electrode 2. The enzyme 13 may be suspended in the measurement solution 3 or may be immobilized on the surface of the working electrode 2. For the immobilization of the enzyme, a physical adsorption method or a chemical bonding method can be used.

  In the transistor-type enzyme sensor shown in FIG. 5, the gate electrode 6 at the transistor site also serves as the working electrode 2. The structure of the top gate transistor is different from the bottom gate transistor shown in FIG. The protective layer 11 was not provided on the gate electrode 6, and a PB electrode film was formed by applying carbon containing Prussin Blue (PB) (C20704424P2, manufactured by Gwent) and baking at 60 ° C. for 30 minutes. Except for the PB electrode film, Teflon (5 wt%, AF1600, manufactured by Mitsui DuPont Fluorochemical Co., Ltd.) was applied and baked at 60 ° C. for 30 minutes to obtain an insulating film. A phosphate buffer solution (pH 7.4) containing 1.4 μL of 10 unit / μL glucose oxidase (manufactured by Wako Pure Chemical Industries, Ltd.) and a hydrochloric acid solution (pH 5.) containing 10 μL of 0.1 wt% chitosan (manufactured by Sigma Aldrich). 4, 0.1 wt%) was mixed, and the total amount of the mixed solution was dropped onto the surface of the PB electrode film and dried at 30 ° C. for 1 hour to obtain an enzyme-modified electrode.

In the transistor type enzyme sensor, the extended gate electrode structure shown in FIGS. 1 to 4 is preferable because only the working electrode 2 is in contact with the measurement solution 3 and can operate stably.
The reference electrode 4 and the working electrode 2 were connected with an external resistance of, for example, 100 KΩ, 220 KΩ, 470 KΩ, and 1 MΩ.

Next, a detection method using the transistor type sensor of the present invention will be described in detail.
The working electrode 2 and the Ag / AgCl reference electrode 4 were immersed in Dulbecco's PBS solution (measuring solution 3, Sigma Aldrich). Control of the voltage between the source electrode 8 and the drain electrode 9 and the voltage of the working electrode 2 and the measurement of the current between the source electrode 8 and the drain electrode 9 and the voltage of the gate electrode 6 are performed using a source meter (manufactured by Keythley). Used. Dulbecco's PBS containing 1M D-glucose (Wako Pure Chemical Industries) was added to the measurement solution stirred at 400 rpm, and the open circuit potential was measured while gradually increasing the final concentration from 0.8 mM to 102.4 mM.

FIG. 6 shows the time change of the voltage generated at the working electrode 2 of the transistor-type enzyme sensor of Example 1. FIG. 7 shows, as a comparative example, time change of voltage generated at the working electrode 2 of a conventional transistor-type enzyme sensor in which the reference electrode 4 and the working electrode 2 are not connected via a resistor. 6 and 7 will be described in detail.
The voltage of the working electrode 2 of the conventional transistor-type enzyme sensor of the comparative example shown in FIG. 7 continued to increase after the addition of glucose. This means that the potential continued to increase as the Prussian blue oxidation reaction with hydrogen peroxide progressed in one direction.

  The voltage of the working electrode 2 of the transistor-type enzyme sensor of Example 1 shown in FIG. 6 is connected to the working electrode 2 and the reference electrode 4 with a resistance of 220 kΩ. Got. This indicates that the steady potential was reached by the balance between the Prussian blue oxidation reaction rate by hydrogen peroxide and the Prussian blue reduction reaction rate by the working electrode 2. The steady-state potential increased with increasing glucose concentration. Thereafter, when the glucose concentration was returned to zero, the steady potential also returned to the potential at the start of the experiment. From the above, the reversibility of the sensor response could be shown.

  Reference electrodes having different standard oxidation-reduction potentials immersed in the measurement solution 3 containing the oxidation-reduction substance 14 and the enzyme 13 from the time change of the voltage generated at the working electrode 2 of the transistor-type enzyme sensor shown in FIGS. 4 and the working electrode 2 were connected by an external resistor 5 to promote a spontaneous regeneration reaction of the electron transfer mediator and to show a reversible response.

  FIG. 8 is a sectional view for explaining a second embodiment of the transistor-type enzyme sensor according to the present invention.

  The difference from the first embodiment of the transistor-type enzyme sensor shown in FIGS. 1 to 5 is that an external capacitor 12 is provided in parallel with the external resistor 5 connected between the reference electrode 4 and the working electrode 2. . The reference electrode 4 and the working electrode 2 were connected by an external capacitor 12 of, for example, 0.047 μF and 1 μF.

FIG. 9 is a result of comparing the time change of the voltage generated at the working electrode 2 of the transistor-type enzyme sensor of Example 2 with and without the external capacitor 12. The external resistance 5 was set to 180 kΩ. The working electrode 2 and the reference electrode 4 were immersed in Dulbecco's PBS (measuring solution 3) containing 10 mM D-glucose, and the voltage change at that time was measured. The external capacitor 12 was not connected for the first 100 seconds of FIG. 9, and the 1 μF external capacitor 12 was connected for the second 100 seconds.
By providing the external capacitor 12 between the reference electrode 4 and the working electrode 2, the basic property that a higher frequency alternating current is easier to pass through is not superimposed on the voltage of the working electrode 2. It can be seen that the noise of the high frequency component is reduced.

  As described above, since the transistor-type enzyme sensor described above can be formed on a flexible substrate, for example, it can be attached to a part of a human body to monitor a change in biological reaction over time with high sensitivity. Furthermore, this sensor can be applied to environmental monitoring and food management.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Working electrode 3 Measurement solution 4 Reference electrode 5 External resistance 6 Gate electrode 7 Gate insulating film 8 Source electrode 9 Drain electrode 10 Organic semiconductor layer 11 Protective layer 12 External capacitor 13 Enzyme 14 Redox substance

Claims (5)

A reference electrode in contact with a measurement solution containing a redox substance and / or an enzyme;
A working electrode that reacts with the redox material and / or enzyme of the measurement solution;
An external resistor provided between the reference electrode and the working electrode;
A gate electrode for inputting a change in voltage of the working electrode, an organic transistor having a semiconductor layer having an organic semiconductor layer, a source electrode, and a drain electrode;
Consisting of
A transistor-type enzyme sensor that detects a change in current between the source electrode and the drain electrode.   The transistor-type enzyme sensor according to claim 1, further comprising an external capacitor between the reference electrode and the working electrode.   3. The transistor-type enzyme sensor according to claim 1, wherein the working electrode is formed integrally with the gate electrode.   4. The transistor-type enzyme sensor according to claim 1, wherein the redox substance is Prussian blue.   5. The transistor-type enzyme sensor according to claim 1, wherein the reference electrode is made of silver / silver chloride.

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