Sensors and compositions

Abstract

This sensor (1) comprises a sensor unit (11) that detects a target substance in a liquid, a current / voltage control means (12), and a current / voltage measurement means (13). The sensor unit includes first and second electrodes (112), (113) disposed adjacently to each other via a gap, and a composition (114) disposed between and in contact with the first and second electrodes. The current / voltage control means and the current / voltage measurement means are electrically connected to the first and second electrodes. The composition contains hydrophilic polymers, conductive fine particles, and an enzyme, and the conductive fine particles and the enzyme are dispersed in the hydrophilic polymers. The content of the conductive fine particles with respect to the total mass of the composition is the ratio of a percolation state of the composition on a mass basis, and a product generated by a reaction between the target substance and the enzyme electrochemically interacts with the conductive fine particles to change an electrical resistance value of the composition.

Description

[Technical Field]

[0001] The present invention relates to a sensor and a composition, and more particularly to a chemiresistive sensor and a composition used therein. [Background technology]

[0002] Electrochemical sensors can be manufactured at low cost, are easy to measure, and enable rapid detection. However, electrochemical sensors require a reference electrode and have a large electrode area, which limits their miniaturization and cost reduction. Among electrochemical sensors, potentiometric sensors require a reference electrode for reliable potential measurement, while amperometric sensors require a reference electrode to apply an accurate potential during measurement. In the case of potentiometric sensors, their response is highly dependent on the stability of the reference electrode. However, a compact solid-state reference electrode with long-term stability has not yet been realized.

[0003] Recently, chemiresistive sensors, conductometric sensors, and field effect sensors have been developed for the purpose of chemical detection.

[0004] A chemiresistive sensor is a resistance-type sensor that detects target molecules by utilizing the change in resistance when the target molecule is adsorbed on the surface of a resistor. Chemiresistive sensors are a simple method for measuring chemical substances. Chemiresistive sensors are expected to be applied to the detection of toxic substances and substances related to specific diseases.

[0005] Patent Document 1 discloses a resistive biosensor in which an enzyme is immobilized on a single-walled carbon nanotube. More specifically, it discloses that glucose oxidase is used as the enzyme, and that hydrogen peroxide produced by the enzyme reaction changes the electrical resistance of the single-walled carbon nanotube to detect glucose.

[0006] Non-Patent Document 1 uses polyaniline, a conductive polymer, as a resistor, and detects glucose by utilizing the change in resistance that accompanies a local pH change around this resistor. Glucose oxidase is dispersed in the resistor. A small amount of platinum nanoparticles is added to oxidize the hydrogen peroxide that is generated when glucose is oxidized by glucose oxidase. In the presence of glucose, the hydrogen peroxide generated as a result of the enzyme reaction reacts with the platinum catalyst, and the generated hydroxide ions (i.e., OH - ) oxidizes the conductive polymer, increasing its resistance. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] U.S. Patent No. 10,031,102 [Non-patent literature]

[0008] [Non-Patent Document 1] Edward Song, Tallis H. da Costa, Jin-Woo Choi, A chemiresistive glucose sensor fabricated by inkjet printing, Microsyst. Technol., 23 (2017) 3505-3511 Summary of the Invention [Problem to be solved by the invention]

[0009] The biosensor of Patent Document 1 is manufactured using a complicated method, and its detection sensitivity is not necessarily high. Furthermore, the chemiresistance sensor of Non-Patent Document 1 utilizes the resistance change of polyaniline due to oxidation, and therefore has low detection sensitivity. Furthermore, the chemiresistance sensor of Non-Patent Document 1 has a very slow response speed, requiring approximately 200 seconds for detection. Furthermore, the bandwidth of the glucose concentration that can be detected is narrow, ranging from 0 to 10 mM.

[0010] An object of the present invention is to provide a sensor that has high detection sensitivity and can be easily manufactured. [Means for solving the problem]

[0011] The present invention includes the following aspects. A sensor comprising a sensor unit for detecting a target substance in a liquid, a current / voltage control means, and a current / voltage measurement means, wherein the sensor unit comprises first and second electrodes arranged adjacent to each other with a gap therebetween, and a composition arranged between the first and second electrodes and in contact with both, the current / voltage control means and the current / voltage measurement means are electrically connected to the first and second electrodes, the composition comprises a hydrophilic polymer, conductive microparticles, and an enzyme, the conductive microparticles and the enzyme are dispersed in the hydrophilic polymer, the content of the conductive microparticles relative to the total mass of the composition is, on a mass basis, a ratio in which the composition is in a percolation state, and a product produced by the reaction between the target substance and the enzyme electrochemically interacts with the conductive microparticles, causing a change in the electrical resistance value of the composition.

[0012] A composition comprising a hydrophilic polymer, conductive microparticles and an enzyme, wherein the conductive microparticles and the enzyme are dispersed in the hydrophilic polymer, and the content of the conductive microparticles relative to the total mass of the composition is, on a mass basis, a proportion in which the composition is in a percolation state. [Effects of the Invention]

[0013] According to the above aspect, it is possible to provide a sensor that has high detection sensitivity and can be easily manufactured, and a composition used for the sensor. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram of a sensor according to an embodiment. [Figure 2] FIG. 2 is a plan view of a sensor unit according to an embodiment. [Figure 3] 3 is a cross-sectional view of the sensor unit of FIG. 2 taken along the line AA'. [Figure 4] 1 is a graph showing the resistance value of a mixture in air using polyvinyl alcohol and platinum nanoparticles versus the mass proportion of platinum nanoparticles in the mixture. [Figure 5A] 5A to 5C are schematic diagrams illustrating a method for manufacturing a sensor according to an embodiment. [Figure 5B] 5A to 5C are schematic diagrams illustrating a method for manufacturing a sensor according to an embodiment. [Figure 5C] 5A to 5C are schematic diagrams illustrating a method for manufacturing a sensor according to an embodiment. [Figure 5D] 5A to 5C are schematic diagrams illustrating a method for manufacturing a sensor according to an embodiment. [Figure 5E] 5A to 5C are schematic diagrams illustrating a method for manufacturing a sensor according to an embodiment. [Figure 6] FIG. 10 is a top view of a sensor unit according to another embodiment. [Figure 7] 1 is a graph showing the resistance value versus the glucose concentration in an aqueous glucose solution in the sensor of Example 1. [Figure 8] 10 is a graph showing the resistance value versus the creatinine concentration in an aqueous creatinine solution in the sensor of Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0015] First Embodiment (sensor) Hereinafter, the embodiments will be described in detail with reference to the drawings. However, the embodiments described below are merely examples, and are not intended to exclude various modifications and applications of techniques not explicitly described in the embodiments. Furthermore, the sizes and ratios of the examples shown in the drawings may be partially enlarged for ease of understanding, and the shapes are also examples. The present invention is not necessarily limited to these. In other words, the present embodiments can be implemented with various modifications within the scope of the spirit thereof.

[0016] A sensor according to one aspect of the present invention includes a sensor section for detecting a target substance in a liquid, a current / voltage control means, and a current / voltage measurement means. 1 is a schematic diagram of a sensor according to a first embodiment. The sensor 1 of this embodiment includes a sensor unit 11, a current / voltage control means 12, and a current / voltage measurement means 13. The sensor unit 11, the current / voltage control means 12, and the current / voltage measurement means 13 are electrically connected.

[0017] Fig. 2 is a plan view of the sensor unit 11 according to the first embodiment as seen from the substrate 111 side. Fig. 3 is a cross-sectional view of the sensor unit 11 taken along the line A-A' in Fig. 2. The sensor unit 11 of this embodiment has a substrate 111, a first electrode 112, a second electrode 113, and a composition 114.

[0018] The substrate 111 can be an insulating substrate, such as a glass substrate, a silicon substrate, or a printed circuit board.

[0019] The first and second electrodes 112 and 113 are located on a substrate 111. The first and second electrodes 112 and 113 are disposed adjacent to each other with a gap therebetween. The gap between the first and second electrodes 112 and 113 is preferably 10 to 100 μm. The first and second electrodes 112 and 113 are conductive metal thin films. The material of the conductive metal thin film is not particularly limited, but examples include gold, silver, chromium, copper, and alloys thereof, or conductive carbon. The conductive metal thin film may be a single layer of the above material, or a multilayer of two or more layers. It is desirable to protect the surfaces of the electrodes 112 and 113 with an insulating resin or the like to prevent leakage current.

[0020] The composition 114 is disposed on the first and second electrodes 112 and 113 and on the substrate 111 so as to fill the gap between the first and second electrodes 112 and 113. The composition 114 is in contact with the first and second electrodes 112 and 113. The composition 114 includes a hydrophilic polymer, conductive particles, and an enzyme. The conductive particles and enzyme are dispersed in the hydrophilic polymer. In other words, the conductive particles extend throughout the gap between the first and second electrodes 112 and 113, at least without short-circuiting. It is preferable that the enzyme be dispersed not only on the surface of the composition 114 but also throughout the composition 114, i.e., inside the composition 114. By having the enzyme located inside the composition 114, the resistance value of the composition 114 can be easily changed by a reaction between the enzyme and the target substance, improving the detection sensitivity of the target substance.

[0021] The hydrophilic polymer is an insulating hydrophilic polymer. Examples of hydrophilic polymers that can be used include polyvinyl alcohol, polyethylene glycol, polyvinyl acetate, and cellulose fiber, with polyvinyl alcohol being preferred. By including a hydrophilic polymer in composition 114, the target substance in the liquid and the enzyme come into contact even inside composition 114, improving the detection sensitivity of the target substance in water. Preferably, the hydrophilic polymer does not expand or contract due to the reaction between the enzyme and the target substance, and can stably hold the conductive microparticles.

[0022] The ratio of the hydrophilic polymer to the total mass of the composition 114 is preferably 20% by mass or more and 90% by mass or less. For example, when the metal fine particles are Pt with a diameter of 2 nm, if the ratio of the hydrophilic polymer to the total mass of the composition 114 is 30% by mass or more and 50% by mass or less, it is easy to control the mass ratio of the conductive fine particles in the composition 114 to be in a percolation state.

[0023] The conductive fine particles are preferably at least one of metal fine particles, graphite fine particles, and graphite wires. Metal fine particles refer to metal particles having a particle diameter of 1 to 80 nm. The particle diameter of the metal fine particles is preferably 1 to 50 nm, and more preferably 1 to 20 nm. The metal fine particles may be any metal fine particles having catalytic activity that promotes the decomposition reaction of an electrode active material (for example, when the target substance is creatinine, hydrogen peroxide solution produced by a cascade reaction) accompanying the reaction of the target substance with an enzyme, and are preferably noble metal fine particles. Specific examples of noble metal fine particles include platinum nanoparticles, gold nanoparticles, silver nanoparticles, and palladium nanoparticles. Of these, platinum nanoparticles are preferred. Graphite fine particles refer to graphite particles having a diameter of 10 to 90 nm. Graphite wires refer to filamentous graphite having a diameter of 1 to 20 nm and a length of 2 to 50 μm (i.e., carbon nanofibers or carbon nanotubes). In this specification, the particle diameter refers to the median diameter (D 50 It is also called.)

[0024] The mass proportion of conductive particles contained in the composition is controlled so that the composition is in a percolation state. A mixture in which conductive particles are added to an insulator such as an insulating polymer changes in electrical conductivity as the proportion of conductive particles increases. When the proportion of conductive particles exceeds a certain level, a conductive path is formed by the connected particles, causing a sudden increase in the electrical conductivity of the mixture. This sudden increase in electrical conductivity is called the percolation phenomenon. The region in which electrical conductivity changes suddenly is highly sensitive to slight changes in carriers. In this embodiment, a sensor with excellent sensitivity can be provided by using a region in which the electrical conductivity of the mixture changes suddenly above a certain level. In this specification, "the composition is in a percolation state" means that the composition contains and disperses conductive particles in a proportion within a range in which the above-mentioned sudden change in electrical conductivity occurs as the density of the conductive particles changes.

[0025] In this embodiment, if the resistance value R of the composition is too large, noise will increase and the composition will not be suitable for measurement. Therefore, when the resistance value of the water-soluble polymer when a constant current or voltage is applied is R1 and the resistance value when an excess amount of conductive fine particles is added to the water-soluble polymer is R2, the resistance value R is preferably in the range of 2.0 × R2 ≦ R ≦ 0.8 × R1, and more preferably (R1 + R2) / 2.5 ≦ R ≦ (R1 + R2) / 1.75.

[0026] For example, Figure 4 is a graph showing the resistance of a mixture in air versus the mass fraction of platinum nanoparticles in a mixture using polyvinyl alcohol as the water-soluble polymer and platinum nanoparticles as the conductive microparticles. The measurement voltage is 0.5 V. The horizontal axis represents the amount of deionized water containing 4% by mass of platinum nanoparticles added to 3 mL of deionized water containing 4% by mass of polyvinyl alcohol. In this example, the resistance value R1 is 1000 MΩ, and the resistance value R2 is 100 MΩ. The resistance value R of the mixture is preferably close to 600 MΩ, for example, between 480 MΩ and 685 MΩ.

[0027] The mass proportion of the conductive microparticles in the composition when it is in a percolation state is preferably such that the resistance value in air of the mixture of the water-soluble polymer and the conductive microparticles is 200 MΩ or more and 800 MΩ or less, more preferably 300 MΩ or more and 750 MΩ or less, even more preferably 500 MΩ or more and 700 MΩ or less, and particularly preferably 550 MΩ or more and 650 MΩ or less.

[0028] Furthermore, the mass ratio of the conductive microparticles when the composition is in a percolation state is preferably a mass ratio that results in a resistance value in water of the mixture of the water-soluble polymer and the conductive microparticles of 0.01 MΩ or more and 10 MΩ or less, and more preferably a mass ratio that results in a resistance value in water of 0.05 MΩ or more and 3 MΩ or less.

[0029] For example, when platinum nanoparticles are used as the conductive microparticles, the mass ratio of the conductive microparticles when composition 114 is in a percolation state is, for example, preferably 30% by mass or more and 75% by mass or less, more preferably 35% by mass or more and 70% by mass or less, and even more preferably 35% by mass or more and 65% by mass or less, as the mass of the conductive microparticles relative to the total mass of composition 114.

[0030] By controlling the mass ratio of the conductive microparticles contained in composition 114 so that the composition is in a percolation state, composition 114 exhibits a large change in resistance even when the electrical change due to the reaction between the target substance and the enzyme is small, thereby improving the sensitivity of the sensor.

[0031] The enzyme is not particularly limited as long as it can be dispersed and supported in a hydrophilic polymer and produces an electrode active material in a reaction between the target substance and the enzyme, and an enzyme capable of detecting the target substance can be appropriately selected. The electrode active material produced by the catalytic reaction of the enzyme is oxidized or reduced by the conductive fine particles, which serve as the electrochemical catalyst, and exchanges charges with the conductive fine particles. Examples of electrode active materials include hydrogen peroxide, oxygen, ammonia, hydrogen, and carbon dioxide. Hydrogen peroxide is an electrode active material that contributes to both oxidation and reduction, and can exchange charges with the conductive fine particles through the following reaction: (Oxidation reaction) H2O2 → O2 + 2H + +2e - (Reduction reaction) H2O2+2H + +2e - →2H2O

[0032] When hydrogen peroxide is oxidized, electrons are donated to the conductive particles, and when hydrogen peroxide is reduced, electrons are removed from the conductive particles, causing them to become positively ionized. For example, ammonia is an electrode active material that is oxidized and releases electrons, and the conductive particles act as an electrochemical catalyst to oxidize it. Alternatively, the pH changes due to the following reduction reaction, which changes the electrical conductivity of composition 114. (Oxidation reaction) 2NH3 → N2(g) + 6H + +6e - (Reduction reaction) NH3 + H2O → NH4 + +OH -

[0033] When the oxidation reaction is dominant, the conductive particles are negatively ionized, and depending on the conditions, the electrons contribute to hopping conduction or tunneling conduction, thereby reducing the resistance of composition 114. Alternatively, when the conductive particles are stable in a negatively charged state due to electrons, the charge caused by the electrification of the conductive particles changes the potential barrier, resulting in a decrease in the electrical conductivity of composition 114. When the reduction reaction is dominant, the conductive particles are positively ionized, and the carriers contributing to electrical conduction decrease, thereby increasing the resistance of composition 114. These oxidation-reduction reactions may occur simultaneously in the conductive particles, in which case electrical conduction occurs in composition 114 in which the conductive particles are dispersed, depending on the concentration of the electrode active material.

[0034] For example, an example of an enzyme that generates hydrogen peroxide and a reaction between the enzyme and a substrate are shown below. (A) Glucose oxidase (also known as GOD) β-D-glucose + O2 → D-glucono-1,5-lactone + H2O2 (B) Protein-lysine-6-oxidase Peptidyl-L-lysyl peptide + O2 + H2O → Peptidyl-lysyl peptide + NH3 + H2O2 (C) Xanthine oxidase Xanthine + H2O + O2 → Uric acid + H2O2 (D) Urate oxidase Uric acid + H2O + O2 → 5-hydroxyisouric acid + H2O2 (E) L-amino acid oxidase L-amino acid + H2O + O2 → 2-oxoacid + NH3 + H2O2 (F) Cholesterol oxidase Cholesterol + O2 → cholest-4-en-3-one + H2O2 (G) Lactate oxidase L-lactate + O2 → Pyruvate + H2O2 (H) Pyruvate oxidase Pyruvate + Phosphate + O2 → Acetylphosphate + CO2 + H2O2 (I) Diamine oxidase Histamine + H2O + O2 → (imidazol-4-yl)acetaldehyde + NH3 + H2O2 (J) Protein-Lysine-6-oxidase Peptidyl-L-lysyl peptide + H2O + O2 → Peptidyl-alisyl peptide + NH3 + H2O2

[0035] The enzyme may be one type or two or more types. When two or more types of enzymes are used, it is not necessary that hydrogen peroxide is produced in all enzyme reactions, as long as an electrode active material is produced in at least one enzyme reaction.

[0036] For example, when the target substance is creatinine, three types of enzymes can be used: creatininase, creatinase, and sarcosine oxidase. (K) Creatininase, creatinase, and sarcosine oxidase (Hydrolysis reaction) Creatinine + H2O → Creatine (Hydrolysis reaction) Creatine + H2O → Sarcosine + Urea (Oxidation reaction) Sarcosine + H2O + O2 → Glycine + HCHO + H2O2

[0037] An example of measuring creatinine using ammonia as an electrode active material is as follows. (L) Creatinine iminohydrolase and creatinine deaminase Creatinine + H2O → N-methylhydantoin + NH3

[0038] The mass ratio of the enzyme to the total mass of the composition 114 is preferably 0.01 mass % or more and 10 mass % or less, more preferably 0.02 mass % or more and 8 mass % or less, and even more preferably 0.05 mass % or more and 5 mass % or less.

[0039] The current / voltage control means 12 and the current / voltage measurement means 13 may be well-known electrochemical measurement devices such as a potentiostat / galvanostat measurement station.

[0040] The sensor 1 may further include a first estimation unit. The first estimation unit controls the current / voltage control means 12 to apply a voltage to the composition 114, and controls the current / voltage measurement means 13 to measure the current value at that time, thereby obtaining a current / voltage curve. The first estimation unit can estimate the electrical resistance value of the composition 114 from the current / voltage curve.

[0041] The sensor 1 may further include a second estimation unit. The second estimation unit controls the current / voltage control means 12 to apply a current to the composition 114, and controls the current / voltage measurement means 13 to measure the voltage value at that time, thereby obtaining a current / voltage curve. The second estimation unit can estimate the electrical resistance value of the composition 114 from the current / voltage curve.

[0042] The sensor having the above configuration can detect target substances in a liquid with high sensitivity.

[0043] (Method for detecting target substances using a sensor) A method for detecting a target substance using a sensor in this embodiment will be described. The sensor unit 11 of the sensor 1 is immersed in a sample, which is a liquid containing the target substance. While slowly stirring the sample, a constant current or voltage is applied using the current / voltage control means 12. As an example, a constant voltage is applied to the sensor 1, and the current value at that time is measured. A calibration curve of the current value versus the mass fraction of the target substance per sample volume is prepared in advance, and the mass fraction of the target substance can be determined from the measured current value. In addition, the electrical resistance value can be estimated by the first estimation unit or the second estimation unit described above.

[0044] In addition to the above-described methods, the sensor of this embodiment can also detect a target substance. For example, after immersing the sensor portion 11 of the sensor 1 in a sample containing the target substance, the current-voltage control means 12 may scan the voltage of the sensor 1 over a predetermined range, the current at that time may be detected by the current-voltage measurement means 13, and the electrical resistance value of the composition 114 may be estimated from the resulting current-voltage curve. Alternatively, the current-voltage control means 12 may scan the current flowing through the sensor 1, the voltage at that time may be detected by the current-voltage measurement means 13, and the electrical resistance value of the composition 114 may be estimated from the resulting current-voltage curve.

[0045] Instead of slowly stirring the sample containing the target substance, the target substance may be continuously brought into contact with the sensor 1 by flowing or circulating a liquid sample. In this case, a liquid delivery pump, a syringe pump, or the like may be used to achieve this.

[0046] (Sensor manufacturing method) An example of a method for manufacturing the sensor 1 of this embodiment will be described below with reference to FIGS. 5A to 5E.

[0047] As shown in FIG. 5A, a conductive metal thin film 115 is formed on a substrate 111. Sputtering can be used as a method for forming the conductive metal thin film 115. In this embodiment, the conductive metal thin film 115 is formed as a single layer, but the conductive metal thin film 115 may be formed as a multilayer of two or more layers. The materials described above can be used as the material for the conductive metal thin film.

[0048] As shown in FIG. 5B, a photoresist layer 116 is formed on the conductive metal thin film 115. As the photoresist, a positive resist or a negative photoresist may be used. As the positive resist, for example, OFPR800 manufactured by Tokyo Ohka Kogyo Co., Ltd. may be used. As the negative resist, for example, OMR83 manufactured by Tokyo Ohka Kogyo Co., Ltd. may be used. In this embodiment, an example using a positive photoresist will be described.

[0049] 5C, the photoresist layer 116 is irradiated with ultraviolet light through a photomask 117. Thereafter, the photoresist layer 116 is developed using a developer to form a photoresist pattern 118.

[0050] 5D, the conductive metal thin film 115 is etched through the photoresist pattern 118 to form the first and second electrodes 112 and 113. A metal etchant can be used as the etching liquid.

[0051] A mixed solution containing a hydrophilic polymer, conductive particles, and an enzyme is prepared. As an example, the hydrophilic polymer, conductive particles, and enzyme are weighed out taking into account their final mass proportions in the composition. The weighed hydrophilic polymer, conductive particles, and enzyme are each added to deionized water to prepare a hydrophilic polymer solution, a conductive particle solution, and an enzyme solution, which are then mixed to prepare a mixed solution. A well-known method may be used to mix the conductive particles and enzyme so that they are dispersed as uniformly as possible within the hydrophilic polymer.

[0052] As shown in FIG. 5E, the mixed liquid is dropped onto the first and second electrodes 112 and 113 and onto the substrate 111 so as to fill the gap between the first and second electrodes 112 and 113. The method for dropping the mixed liquid is not particularly limited, but inkjet is preferred. After dropping the mixed liquid, the mixture is dried to form a composition 114. In the composition 114 thus formed, conductive particles are dispersed in a hydrophilic polymer, and an enzyme is supported by the hydrophilic polymer.

[0053] The first and second electrodes 112 and 113 are connected to the current / voltage control means 12 and the current / voltage measurement means 13 by wiring, and the sensor 1 is completed.

[0054] Second Embodiment The sensor of this embodiment differs from the first embodiment in the configuration of the sensor unit. Other aspects of the sensor configuration are the same as those of the first embodiment, so a description thereof will be omitted. Fig. 6 is a top view of the sensor unit according to this embodiment. The sensor unit 11' of this embodiment includes first to third electrodes 112, 113, and 119, a composition 114, and a reference composition 120.

[0055] The second electrode 113 is disposed adjacent to the first electrode 112 with a gap therebetween, and is also disposed adjacent to the third electrode 119 with a gap therebetween. The reference composition 120 is disposed on the second and third electrodes 113 and 119 and on the substrate 111 so as to fill the gap between the second and third electrodes 113 and 119. The reference composition 120 is in contact with the second and third electrodes 113 and 119.

[0056] The third electrode 119 is a conductive thin film identical to the first and second electrodes 112 and 113. The reference composition 120 is a mixture of hydrophilic polymer and conductive microparticles, the same as composition 114, except that it does not contain the enzyme.

[0057] In this embodiment, the first and second electrodes 112 and 113 and the composition 114 are the target substance detection element, and the second and third electrodes 113 and 119 and the reference composition 120 are the reference element. By subtracting the resistance value of the reference element from the resistance value of the target substance detection element, the resistance value of the composition 114 can be corrected, and the influence of fluctuations in the resistance value due to impurities in the sample containing the target substance can be suppressed. [Example]

[0058] The present invention will be further explained below with reference to examples, but the present invention is not limited to these examples in any way.

[0059] Example 1 A 20 nm-thick chromium thin film was formed on a Tempax glass substrate using a sputtering system (Shibaura Mechatronics, CFS-4ES). A 0.1 μm-thick gold thin film was then formed on this chromium thin film using a sputtering system (Shibaura Mechatronics, CFS-4ES). A positive photoresist (Tokyo Ohka Kogyo, product number OFPR800-30CP) was applied to the gold thin film, irradiated with ultraviolet light through a photomask, and developed using a developer to form a photoresist pattern. The first and second electrodes were then fabricated by etching and patterning the metal using a gold and chromium etchant. The shortest distance between the first and second electrodes was 50 μm.

[0060] Mixed solution 1 was prepared by mixing platinum nanoparticles (Tanaka Kikinzoku Co., Ltd., particle size: 2 nm) with deionized water. The platinum nanoparticles accounted for 4 mass% of the mass of mixed solution 1. Mixed solution 2 was prepared by mixing polyvinyl alcohol (Fujifilm Wako Pure Chemical Industries, Ltd.) with deionized water and adding 0.6 wt% boric acid to crosslink and stabilize the polyvinyl alcohol. The polyvinyl alcohol accounted for 4 mass% of the mass of mixed solution 2. Mixed solution 3 was prepared by mixing 0.11 mg (30 mU) of glucose oxidase (Nacalai Tesque, Inc., product number: 16831-01) with 1 mL of deionized water.

[0061] The liquid obtained by mixing Mixtures 1 to 3 was dropped using a pipette into the gap between the first and second electrodes and onto the edges of the first and second electrodes, and dried at 45°C for 60 minutes to form a composition with a thickness of 5 to 10 µm. The first and second electrodes and composition thus formed on the glass substrate served as the sensor part.

[0062] The first and second wires were connected to the first and second electrodes, respectively. A current-voltage control means (manufactured by Keithley, product number: 2400) and a current-voltage measurement means (manufactured by Keithley, product number: 2400) were connected between the first and second wires to manufacture the sensor.

[0063] The sensor part of the manufactured sensor was immersed in glucose aqueous solutions with glucose concentrations of 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, and 0.5 mol / L, respectively, and a constant current of 640 μA was applied using a current-voltage control means. The resistance value of the sensor part was obtained from the voltage value at that time. Figure 7 is a graph showing the resistance value of the sensor part versus the glucose concentration in the glucose aqueous solution for the sensor of Example 1. It was found that the resistance value of the sensor part decreased as the concentration of glucose contained in the sample increased.

[0064] Example 2 First and second electrodes were fabricated on a glass substrate by the method described in Example 1. Mixture 4 was prepared by mixing 0.5 mg of creatininase (Sigma-Aldrich, product number: C3921-500UN), 5.7 mg of creatinase (Sigma-Aldrich, product number: C3172-1KU), and 2.3 mg of sarcosine oxidase (Sigma-Aldrich, product number: S7897-1KU) in 1 mL of deionized water.

[0065] The liquid obtained by mixing mixed solutions 1, 2, and 4 was dropped using a pipette so as to cover the gap between the first and second electrodes and the ends of the first and second electrodes, and the sensor part was produced by drying at 45°C for 60 minutes. The manufacturing procedures for the sensor other than the sensor part were the same as in Example 1.

[0066] The sensor portion of the manufactured sensor was immersed in creatinine aqueous solutions with creatinine concentrations of 0 mg / dL, 3 mg / dL, 6 mg / dL, 25 mg / dL, 50 mg / dL, 75 mg / dL, 100 mg / dL, 150 mg / dL, 200 mg / dL, 250 mg / dL, and 300 mg / dL, respectively, and a voltage of 0.1 to 1.0 V was applied in 0.1 V increments using the current / voltage control means. The resistance value of the sensor portion was obtained from the current value at that time. Figure 8 is a graph showing the resistance value of the sensor portion versus the creatinine concentration in the creatinine aqueous solution for the sensor of Example 2. It was found that the resistance value of the sensor portion decreased as the creatinine concentration in the sample increased.

[0067] Although the above description has been given using glucose and creatinine as examples of target substances, the present invention is not limited thereto. Target substances include peptidyl-L-lysyl peptide, xanthine, uric acid, L-amino acids, cholesterol, L-lactate, pyruvic acid, histamine, and peptidyl-L-lysyl peptide, and can be measured using the following enzymes: protein-lysine-6-oxidase, xanthine oxidase, uric acid oxidase, L-amino acid oxidase, cholesterol oxidase, lactate oxidase, pyruvic acid oxidase, diamine oxidase, and protein-lysine-6-oxidase, respectively. [Industrial Applicability]

[0068] According to the above aspect, it is possible to provide a sensor that has high detection sensitivity and can be easily manufactured, and a composition used for the sensor. [Explanation of symbols]

[0069] 1...sensor, 11, 11'...sensor portion, 12...current / voltage control means, 13...current / voltage measuring means, 111...substrate, 112...first electrode, 113...second electrode, 114...composition, 115...conductive metal thin film, 116...photoresist layer, 117...photomask, 118...photoresist pattern, 119...third electrode, 120...reference composition

Claims

1. A sensor comprising a sensor unit for detecting a target substance in a liquid, a current / voltage control means, and a current / voltage measurement means, The sensor unit includes first and second electrodes disposed adjacent to each other with a gap therebetween; a composition disposed between and in contact with the first and second electrodes; the current / voltage control means and the current / voltage measurement means are electrically connected to the first and second electrodes, the composition comprises a hydrophilic polymer, conductive microparticles and an enzyme; the conductive fine particles and the enzyme are dispersed in the hydrophilic polymer; the content of the conductive fine particles relative to the total mass of the composition is, on a mass basis, a proportion in which the composition is in a percolation state; A sensor in which a product produced by the reaction between the target substance and the enzyme electrochemically interacts with the conductive fine particles, causing a change in the electrical resistance of the composition.

2. The sensor of claim 1 , wherein the hydrophilic polymer is an insulating polymer.

3. 3. The sensor according to claim 1, wherein the conductive particles are at least one of metal particles, graphite particles, and graphite thin wires.

4. The sensor unit further includes a third electrode disposed adjacent to the second electrode with a gap therebetween; 3. The sensor according to claim 1, further comprising a reference composition disposed between the second electrode and the third electrode, the reference composition comprising a mixture of a hydrophilic polymer and conductive particles.

5. further comprising a first estimator; the first estimation unit applies a voltage to the composition using the current-voltage control means and measures the current value at that time using the current-voltage measurement means to obtain a current-voltage curve; The sensor according to claim 1 or 2, wherein the first estimating unit estimates the electrical resistance value of the composition from the current-voltage curve.

6. Further, a second estimation unit is included, the second estimation unit applies a current to the composition using the current-voltage control means and measures the voltage value at that time using the current-voltage measurement means to obtain a current-voltage curve; The sensor according to claim 1 or 2, wherein the second estimation unit estimates the electrical resistance value of the composition from the current-voltage curve.

7. A composition comprising a hydrophilic polymer, a conductive microparticle, and an enzyme, the conductive fine particles and the enzyme are dispersed in the hydrophilic polymer; A composition in which the content of the conductive fine particles relative to the total mass of the composition is a proportion by mass that causes the composition to be in a percolation state.

Images