Electrochemical sensor and method of manufacturing an electrochemical sensor

Abstract

An electrochemical sensor includes a working electrode, a counter electrode, and a substrate supporting the working electrode and the counter electrode, the working electrode is a chip-shaped electrode having a diamond film and a support, a redox reaction occurs on the surface of the diamond film when a predetermined voltage is applied between the working electrode and the counter electrode in the presence of a test sample, the support is formed of a material other than diamond and supports the diamond film, and the working electrode is mounted on the substrate with the support on the substrate side and at least a part of the side surface of the support exposed.

Description

Technical Field

[0001] This invention relates to electrochemical sensors and methods for manufacturing electrochemical sensors. Background Technology

[0002] In recent years, electrodes with diamond films have been proposed as working electrodes for electrochemical sensors (see, for example, Patent Documents 1 and 2). Because conductive diamond has a wide potential window and low background current, it can be used for the electrochemical detection of various substances such as uric acid with high sensitivity. Therefore, conductive diamond has attracted attention as a material for forming working electrodes.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2007-292717

[0006] Patent Document 2: Japanese Patent Application Publication No. 2013-208259 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] The purpose of this invention is to provide an electrochemical sensor with a working electrode having a diamond film that can perform accurate sensing even with a simple structure.

[0009] Methods for solving problems

[0010] This invention provides an electrochemical sensor and related technologies, the electrochemical sensor comprising:

[0011] Working electrode;

[0012] counter electrode; and

[0013] The substrate supports the working electrode and the counter electrode.

[0014] The aforementioned working electrode is a chip-shaped electrode having a diamond film and a support. When a predetermined voltage is applied between the working electrode and the aforementioned counter electrode with a test sample present, a redox reaction occurs on the surface of the aforementioned diamond film. The aforementioned support is formed of a material other than diamond and supports the aforementioned diamond film.

[0015] The working electrode is mounted on the substrate with the support located on the substrate side and at least a portion of the side of the support exposed.

[0016] Invention Effects

[0017] According to the present invention, an electrochemical sensor having a working electrode with a diamond film can be provided, which can perform accurate sensing even with a simple structure. Attached Figure Description

[0018] Figure 1 This is an example of a perspective view of an electrochemical sensor according to one embodiment of the present invention.

[0019] Figure 2 Therefore Figure 1 The AA-line cross-sectional view is a diagram showing a simplified configuration of an electrochemical sensor according to one embodiment of the present invention.

[0020] Figure 3 (a) is a schematic diagram showing the formation of a diffusion layer on a high aspect ratio working electrode. Figure 3 (b) is a schematic diagram showing the formation of a diffusion layer on a working electrode with a low aspect ratio.

[0021] Figure 4 This is a schematic diagram of the vapor phase growth apparatus used to grow diamond films.

[0022] Figure 5 (a) is a diagram showing the cross-sectional structure of the diamond film and substrate laminate. Figure 5 (b) indicates that in Figure 5 (a) is a cross-sectional view of the laminated body shown in the figure, in which a concave groove is formed on the back side. Figure 5 (c) is a schematic diagram showing the process of obtaining a working electrode by breaking the diamond film along the concave groove.

[0023] Figure 6 (a) shows the cyclic voltammogram obtained when measuring uric acid concentration in sample 1. Figure 6 (b) shows the cyclic voltammogram obtained when determining the uric acid concentration in sample 2. Figure 6 (c) shows the cyclic voltammogram obtained when measuring uric acid concentration in sample 3.

[0024] Figure 7 (a) is a schematic diagram showing the peripheral portion of the working electrode of sample 1. Figure 7 (b) is a schematic diagram showing the periphery of the working electrode of sample 2. Figure 7 (c) is a schematic diagram showing the periphery of the working electrode of sample 3.

[0025] Figure 8 Cyclic voltammetry diagrams are shown for samples using working electrodes that have undergone sufficient deactivation treatment and samples using working electrodes that have not undergone sufficient deactivation treatment. Detailed Implementation

[0026] Before describing the embodiments of the present invention, the insights obtained by the inventors of this application will be explained.

[0027] As the working electrode of an electrochemical sensor used in electrochemical measurements, a laminate of a support made of a conductive material such as silicon (Si) and a diamond film has been proposed. Here, the conductive material refers to a material sandwiched between the diamond film and the working electrode circuit that enables electrical connection between the two. Such an electrochemical sensor is configured such that, with a test sample (e.g., a liquid containing uric acid such as urine) adhering to the surface of the diamond film, a predetermined voltage is applied between the working electrode and the counter electrode, causing a redox reaction (electrochemical reaction) of a predetermined component (uric acid, etc.) in the test sample to occur on the surface of the diamond film. The concentration of the predetermined component in the test sample is determined by measuring the current flowing through this redox reaction. Such an electrochemical sensor typically sets the working electrode so that the test sample does not adhere to the sides of the support. For example, when setting the working electrode, the sides of the support are usually covered with an insulating (waterproof) material so that the sides of the support are not exposed. This is because when a redox reaction of a specified component of the test sample occurs on the surface of the diamond film, if the test sample adheres to the side of the support, a redox reaction also occurs on the side of the support, which is made of a conductive material. In this case, the measured current value includes the current value caused by the redox reaction occurring on the surface of the diamond film and the current value caused by the redox reaction occurring on the side of the support. Therefore, it is sometimes impossible to accurately measure the concentration of the specified component in the test sample. That is, the sensitivity of the electrochemical sensor sometimes decreases.

[0028] However, the inventors of this application discovered that even for electrochemical sensors with exposed sides of the silicon substrate serving as the support, the sensitivity does not uniformly deteriorate within a voltage range (greater than 0 volts (V) and less than 1 volt (V), preferably more than 0.5 V and less than 0.7 V) applied between the working electrode and the counter electrode with the diamond film when measuring the uric acid concentration in the test sample; rather, the sensitivity exhibits a large deviation. Therefore, a detailed investigation was conducted on the working electrodes of the electrochemical sensors where sensitivity deviations occurred. The results showed that the degree of redox reaction occurring on the sides of the support varied. The working electrode with the smallest decrease in sensor sensitivity exhibited significant deactivation on the support sides, where the redox reaction was suppressed, and an insulating silicon oxide film formed in the aforementioned inactive portion. These are the results of in-depth research conducted by the inventors of this application and represent a first-time discovery.

[0029] Based on these results, the inventors of this application discovered that when a laminate having a diamond film and a conductive support is used as the working electrode, and the voltage applied between the working electrode and the counter electrode is within the aforementioned voltage range, if the entire side of the support is covered with an insulating film such as an oxide film to deactivate it, then even if the side of the support is not specifically covered with other insulating materials, that is, even if the support is exposed, redox reactions such as uric acid will not occur on the support.

[0030] This invention is based on the above-mentioned insights discovered by the inventors of this application.

[0031] <One embodiment of the present invention>

[0032] Hereinafter, as one embodiment of the present invention, reference is made to... Figures 1-5 An electrochemical sensor for determining the concentration of a specified component in a liquid test sample (electrolyte) using a three-electrode method will be described. In this embodiment, an electrochemical sensor for determining the concentration of uric acid in a liquid containing uric acid, such as urine, using a three-electrode method will be used as an example.

[0033] (1) Composition of electrochemical sensors

[0034] like Figure 1 As shown, the electrochemical sensor 100 of this embodiment (hereinafter also referred to as "sensor 100") is configured to include a substrate 10, an electrode group 20 consisting of a working electrode 21 supported by the substrate 10, a counter electrode 22 and a reference electrode 23, and wiring 31 to 33 connected to the working electrode 21, the counter electrode 22 and the reference electrode 23 respectively.

[0035] The substrate 10 is configured to support the working electrode 21, the counter electrode 22, and the reference electrode 23, i.e., the electrode assembly 20. The substrate 10 is configured as a sheet (plate) member. The planar shape of the substrate 10 can be, for example, rectangular. The substrate 10 has physical (mechanical) strength sufficient to function as a sensor 100, for example, strength that prevents bending or breakage even when a test sample is attached. The substrate 10 can be formed, for example, from insulating materials such as composite resin, ceramic, glass, plastic, flammable material, biodegradable material, nonwoven fabric, or paper. The substrate 10 is preferably a flexible substrate. For example, a substrate formed of glass epoxy resin or polyethylene terephthalate (PET) can be suitable as the substrate 10. Alternatively, a semiconductor substrate or a metal substrate configured to have insulation on the surfaces supporting the electrode assembly 20 can also be used as the substrate 10.

[0036] A working electrode 21 is disposed on either of the two main surfaces of the substrate 10. The working electrode 21 is disposed near one end of the substrate 10 in the longitudinal direction. The working electrode 21 is configured as a laminate having a diamond film 211 and a support 212 supporting the diamond film 211 (see reference). Figure 2 The working electrode 21 is disposed on the substrate 10 with the support 212 located on the substrate 10 side. The sensor 100 having the working electrode 21 with the diamond film 211 is also referred to as a diamond sensor. It should be noted that the details of the structure of the working electrode 21 will be described later.

[0037] Hereinafter, the surface on which the working electrode 21 is disposed of among the two main surfaces of the substrate 10 will be referred to as the "upper surface of the substrate 10".

[0038] The working electrode 21 is mounted (bonded) to the substrate 10 via a conductive adhesive 14. For example, conductive pastes such as solder, silver (Ag) paste, copper (Cu) paste, anisotropic conductive paste, or anisotropic conductive film such as ACF film can be used as the conductive adhesive 14. Furthermore, the conductive adhesive 14 is covered with an insulating (waterproof) material (hereinafter also referred to as insulating material 15) to prevent the conductive adhesive 14 from being exposed. The insulating material 15 is provided so that the conductive adhesive 14 is not exposed and at least a portion of the side surface of the support 212 is exposed. That is, the working electrode 21 is mounted on the substrate 10 with the support 212 located on the substrate 10 side and at least a portion of the side surface of the support 212 exposed, not covered by the insulating material 15.

[0039] As described above, the inventors of this application have conducted in-depth research and have found that, within the voltage range applied when measuring uric acid concentration (greater than 0V and less than 1V, preferably a voltage range of more than 0.5V and less than 0.7V), if the surface (including the side surface) of the support 212 is inactive, no redox reaction will occur for uric acid or the like. Therefore, even when the working electrode 21 is disposed on the substrate 10 with at least a portion of the side surface of the support 212 exposed, the uric acid concentration can be accurately measured using a diamond sensor.

[0040] Additionally, a counter electrode 22 and a reference electrode 23 are provided on the upper surface of the substrate 10. The counter electrode 22 and the reference electrode 23 are located near the working electrode 21.

[0041] The counter electrode 22 is configured to surround the working electrode 21 and the reference electrode 23. The counter electrode 22 can be an electrode made of metals such as platinum (Pt), gold (Au), copper (Cu), palladium (Pd), nickel (Ni), and silver (Ag), or a carbon electrode. The counter electrode 22 can be formed using known methods such as semi-addition or subtraction methods.

[0042] With the test sample attached to the working electrode 21 and the counter electrode 22, a predetermined voltage is applied between the working electrode 21 and the counter electrode 22 using a measuring mechanism having a voltage application unit described later. A redox reaction of a predetermined component (a predetermined reaction species, such as uric acid) in the test sample occurs between the working electrode 21 and the counter electrode 22, thereby allowing current to flow between the working electrode 21 and the counter electrode 22. Hereinafter, "with the test sample attached, a predetermined voltage is applied between the working electrode 21 and the counter electrode 22 using a measuring mechanism having a voltage application unit described later" will be simply described as "applying a predetermined voltage".

[0043] The reference electrode 23 serves as a reference electrode for determining the potential of the working electrode 21. For example, a silver / silver chloride (Ag / AgCl) electrode can be used as the reference electrode 23. Alternatively, a standard hydrogen electrode, a reversible hydrogen electrode, a palladium-hydrogen electrode, a saturated calomel electrode, or a carbon electrode can also be used. Furthermore, electrodes formed of metals such as Pt, Au, Cu, Pd, Ni, and Ag can also be used as the reference electrode 23. The reference electrode 23 can be formed using known methods such as die-spreading or screen printing.

[0044] One end of the working electrode 21 is connected to a wiring (conductor wiring) 31, one end of the counter electrode 22 is connected to a wiring (conductor wiring) 32, and one end of the reference electrode 23 is connected to a wiring (conductor wiring) 33. Wirings 31 to 33 are respectively disposed on the upper surface of the substrate 10. That is, wirings 31 to 33 are respectively supported on the substrate 10.

[0045] Wiring 31 is formed using a conductive material and is separate from the working electrode 21. Wiring 31 can be formed using, for example, Cu. Besides Cu, wiring 31 can also be formed using various noble metals such as Au, Pt, Ag, or Pd, various metals such as aluminum (Al), iron (Fe), Ni, chromium (Cr), and titanium (Ti), alloys with these noble metals or metals as the main component, oxides of the aforementioned noble metals or alloys, metal oxides, etc. Alternatively, wiring 31 can also be formed using carbon. Wiring 31 is electrically connected to the working electrode 21 via a conductive adhesive 14 (see reference). Figure 2 The conductive adhesive 14 and wiring 31 are preferably covered by the aforementioned insulating material 15 (see reference). Figure 2 ).

[0046] Wiring 32 can be formed using the same material as counter electrode 22, a material containing the same material, or a conductive material different from the material forming counter electrode 22. For example, wiring 32 can be formed using the same material as illustrated in wiring 31. Wiring 32 can be formed integrally with or separately from counter electrode 22. In the case where wiring 32 is formed separately from counter electrode 22, wiring 32 can be electrically connected to counter electrode 22 using the same adhesive as conductive adhesive 14.

[0047] The wiring 33 can be formed using the same material as the reference electrode 23, a material containing the same material, or a conductive material different from the material formed by the reference electrode 23. For example, the wiring 33 can be formed using the same material as exemplified in the wiring 31. The wiring 33 can be formed integrally or separately from the reference electrode 23. In the case where the wiring 33 is formed separately from the reference electrode 23, the wiring 33 can be electrically connected to the reference electrode 23 using the same adhesive as the conductive adhesive 14.

[0048] Wiring 31 to 33 can also be formed by plating Au or Ag on a conductor pattern formed by subtractive or semi-additive methods. In addition to subtractive methods, wiring 31 to 33 can also be formed by printing methods such as screen printing, gravure printing, offset printing, inkjet printing, and vapor deposition.

[0049] Wiring 31 to 33 may have the same structure or different structures. For example, wiring 31 to 33 may be formed of the same material or different materials.

[0050] (2) Composition of the working electrode

[0051] The following is mainly based on Figure 2 and Figure 3 The configuration of the working electrode 21 in this embodiment will be described.

[0052] like Figure 2 As shown, the working electrode 21 is configured as a laminate having a diamond film 211 and a support 212 supporting the diamond film 211. When a predetermined voltage is applied between the working electrode 21 and the counter electrode 22 using a measuring mechanism having, for example, a voltage application part described later, with a test sample (electrolyte) attached to the diamond film 211, a redox reaction of a predetermined component (a predetermined reaction species, such as uric acid) in the test sample occurs on the surface. As described above, the working electrode 21 is disposed on the substrate 10 such that the support 212 is located on the substrate 10 side.

[0053] Diamond film 211 is a polycrystalline film. Diamond film 211 can also be a diamond-like carbon (DLC) film. When the term "diamond film 211" is used in this specification, it includes the case of a polycrystalline diamond film, the case of a DLC film, and the case of both. Diamond film 211 is preferably p-type. To form a p-type diamond film 211, diamond film 211 is preferably, for example, 1 × 10⁻⁶. 19 cm -3 Above and 1×10 22 cm -3 The following concentrations include elements such as boron (B). The B concentration in the diamond film 211 can be determined, for example, by secondary ion mass spectrometry (SIMS). The diamond film 211 can be grown (synthesized) using chemical vapor deposition (CVD) methods such as hot filament CVD and plasma CVD, or physical vapor deposition (PVD) methods such as ion beam CVD and ionization evaporation. When using hot filament CVD to grow the diamond film 211, tungsten wire can be used as the filament, for example. The thickness of the diamond film 211 can be set to be, for example, 0.5 μm or more and 10 μm or less, preferably 2 μm or more and 4 μm or less.

[0054] The support 212 is formed using a material other than diamond (a dissimilar material). The support 212 is preferably made of a conductive material. For example, the support 212 is preferably made of elemental silicon (Si) or a silicon compound. That is, the support 212 is preferably made of a silicon substrate. Specifically, the support 212 is preferably made of any one of a single-crystal Si substrate, a polycrystalline Si substrate, or a silicon carbide substrate (SiC substrate).

[0055] The support 212 is preferably made of a substrate with low resistivity. The support 212 is preferably made of a material with a resistivity of 0.04 Ωcm or less, that is, the resistivity of the support 212 is preferably 0.04 Ωcm or less.

[0056] This is because the current generated by the redox reaction of uric acid described above (hereinafter also referred to as the "reaction current") flows from the surface of the working electrode 21, i.e., the diamond film 211, through the support 212 to the wiring 31. In such a reaction current flow path, the external resistance is preferably as low as possible.

[0057] Examples of components of external resistance include (1) the resistance of the electrolyte between the working electrode 21 and the reference electrode 23, (2) the resistance of the interface between the working electrode 21 (diamond film 211) and the surface of the support 212, (3) the resistance of the support 212 itself, (4) the connection resistance (contact resistance) between the back side of the support 212 and the conductive adhesive 14 (the metal component (metal filler) in the conductive adhesive 14), (5) the connection resistance between the conductive adhesive 14 and the wiring 31, and (6) the wiring resistance. By making the distance between the working electrode 21 and the reference electrode 23 less than 5 mm, the resistance of (1) can be sufficiently reduced. The resistances of (4) to (6) are generally so low as to be negligible. By using a substrate with low resistivity as the support 212, the resistances of (2) and (3) can be sufficiently reduced to be negligible. Specifically, by making the resistivity of the support 212 below 0.04 Ωcm, the resistances of (2) and (3) can be sufficiently reduced. Therefore, in the aforementioned reaction current flow path, the external resistance can be reduced, and the variation in the value of the reaction current caused by the external resistance can be minimized. As a result, the concentration of uric acid in the test sample can be determined more accurately.

[0058] Furthermore, the external resistance, particularly the resistance described in (4) above, is preferably less than 10% of the resistance caused by electron transfer at the liquid-interface of the working electrode 21 surface associated with the redox reaction of uric acid (the oxidation reaction of uric acid) (hereinafter also referred to as "liquid-interface resistance"). This reliably reduces the variation in the reaction current value caused by the external resistance. As a result, the concentration of uric acid in the test sample can be determined more accurately. If the resistance described in (4) above exceeds 10% of the liquid-interface resistance, the external resistance component is added to the reaction current (redox current) curve on the cyclic voltammogram obtained by the cyclic voltammetry method described later, and sometimes the peak current value becomes smaller. Therefore, the concentration of uric acid in the test sample cannot always be determined accurately.

[0059] From the viewpoint of setting the resistance of (4) to less than 10% of the liquid-interface resistance, it is also preferable to use a support 212 with a resistivity of, for example, less than 0.04 Ωcm.

[0060] Here, with the working electrode 21 having a diamond film 211, the liquid-interface resistance varies slightly depending on the measurement conditions, but is typically around 120 Ωcm. 2 Therefore, in this embodiment, the resistance of (4) is preferably 12 Ωcm. 2 The following should be noted: the planar area of ​​the working electrode 21 is 4 mm². 2 In the case of (2mm) In the case of a chip-shaped working electrode 21, the liquid-interface resistance varies slightly depending on the measurement conditions, but is approximately 3kΩ.

[0061] To set the resistance of (4) to 12Ωcm 2 Hereinafter, the carrier concentration in the support 212 will be set to, for example, 1 × 10⁻⁶. 18 cm -3 That's all. If the carrier concentration in the support 212 is set to, for example, 1 × 10⁻⁶... 18 cm -3 Therefore, the resistivity of the support 212 can be set to, for example, 0.04 Ωcm or less. As a result, as described above, the resistance of (4) can be set to 12 Ωcm. 2 The following is a further explanation. Additionally, it is preferable to set the carrier concentration in the support 212 to 1 × 10⁻⁶. 19 cm -3 That's all. If the carrier concentration in support 212 is made to be 1 × 10⁻⁶... 19 cm -3 The resistivity of the support 212 can be made below 0.009 Ωcm, which further reduces the resistance of (4). Furthermore, it is even more preferable to set the carrier concentration in the support 212 to 5 × 10⁻⁶. 19 cm -3 That's all. If the carrier concentration in support 212 is made to be 5 × 10⁻⁶... 19 cm -3 In this way, the resistivity of the support 212 can be reduced to below 0.003 Ωcm, which results in a significant reduction in the resistance of (4).

[0062] It should be noted that the inventors of this application have confirmed that when a silicon substrate with a resistivity of, for example, 10 Ωcm (i.e., a silicon substrate with high resistivity) is used as the support 212, the resistance of (4) becomes high, and as a result, it is sometimes difficult to make the resistance of (4) less than 10% of the liquid-interface resistance.

[0063] The lower limit of the resistivity of the support 212 can be set, for example, to 0.001 Ωcm. This is because it is preferable to dope the support 212 with boron (B) in the same way as the diamond film 211, as an impurity to make the support 212 p-type. If it is desired that the resistivity of the support 212 is less than 0.001 Ωcm, then the support 212 (silicon substrate) needs to be doped with more than 1.5 × 10⁻⁶ Ω·cm. 20 cm -3The dopant (B) is present. However, a support 212 containing a high concentration of dopant not only tends to have a lower yield rate in crystal manufacturing, but also increases the likelihood of crystal defects such as dopant precipitates, potentially degrading the performance of the support 212. Therefore, the resistivity of the support 212 is preferably 0.001 Ωcm or higher.

[0064] By doping the support 212 with boron (B), the resistivity of the support 212 can be reliably reduced. The support 212 is preferably doped with boron (B) at a density of 5 × 10⁻⁶. 18 cm -3 Above and 1.5×10 20 cm -3 The following concentrations contain B, more preferably 5 × 10⁻⁶. 18 cm -3 Above and 1.2×10 20 cm -3 The following concentrations include B. This is achieved by setting the B concentration in support 212 to 5 × 10⁻⁶. 18 cm -3 The above methods reliably ensure that the resistivity of the support 212 is below 0.04 Ωcm. This is achieved by maintaining the boron concentration in the support 212 at 1.5 × 10⁻⁶. 20 cm -3 Below, the resistivity of the support 212 can be set to approximately 0.001 Ωcm, and the decrease in manufacturing yield and performance degradation of the support 212 can be suppressed. This is achieved by setting the boron concentration in the support 212 to 1.2 × 10⁻⁶. 20 cm -3 The following concentration can set the resistivity of the support 212 to about 0.001 Ωcm and reliably suppress the decrease in manufacturing yield and performance degradation of the support 212.

[0065] The sides of the support 212 are preferably configured such that uric acid electrolysis (uric acid redox reaction) does not occur on the sides when a specified voltage is applied. For example, the sides of the support 212 are preferably deactivated. Here, "the sides of the support 212 are deactivated" means that the sides of the support 212 have been treated to suppress the uric acid redox reaction on the sides of the support 212 when a specified voltage is applied (deactivation treatment). As long as at least the surface layer of the sides of the support 212 is deactivated, it is sufficient. The deactivation of the sides of the support 212 is carried out by forming an insulating film (insulating film) 213 on the sides of the support 212.

[0066] For example, by oxidizing or nitriding the side surfaces of the support 212, the side surfaces of the support 212 can be deactivated. In this case, the insulating film 213 is, for example, a region where the Si-containing support 212 is oxidized to become silicon oxide (SiO2 region), or a region where the Si-containing support 212 is nitrided to become silicon nitride (SiN region).

[0067] The insulating film 213 is a continuous film that covers the entire side of the support 212. Thus, even if the working electrode 21 is disposed on the substrate 10 with at least a portion of the side of the support 212 exposed, the redox reaction of uric acid on the side of the support 212 can be reliably suppressed when a specified voltage is applied.

[0068] The thickness of the insulating film 213 (e.g., the thickness of the surface portion of the side of the oxidized or nitrided support 212) can be set to 1 nm or more, preferably 2 nm or more. If the thickness of the insulating film 213 is 1 nm or more, it can be made into a continuous film, covering the entire side of the support 212 without exposing it. As a result, the effect of suppressing the redox reaction of uric acid occurring on the side of the support 212 when a specified voltage is applied can be obtained. By making the thickness of the insulating film 213 2 nm or more, it is possible to reliably make the insulating film 213 into a continuous film, and the aforementioned effect of suppressing the redox reaction of uric acid can be reliably obtained. It should be noted that if the thickness of the insulating film 213 becomes extremely thick, the conductive area of ​​the support 212 becomes smaller. Therefore, the thickness of the insulating film 213 is preferably the thinnest possible thickness to obtain the aforementioned effect of suppressing the redox reaction of uric acid.

[0069] The thickness of the support 212 can be, for example, 350 μm or more. This improves the sensing sensitivity of electrochemical measurements (hereinafter also referred to as "sensing sensitivity").

[0070] This is because, with a constant planar area of ​​the working electrode 21, the thicker the support 212, the higher the aspect ratio (height / width) of the working electrode 21 (high aspect ratio electrode); conversely, the thinner the support 212, the lower the aspect ratio of the working electrode 21 (low aspect ratio electrode). Simultaneously with the application of voltage to the working electrode 21, uric acid, as a reactant, diffuses, forming a diffusion layer (diffusion layer of reactants) 214 of uric acid on the working electrode 21 (diamond film 211). At this time, in a high aspect ratio electrode, uric acid exhibits cylindrical diffusion, spherical diffusion, etc., which can be considered as two-dimensional or three-dimensional diffusion. Therefore, the diffusion layer 214 becomes approximately spherical in shape (see reference). Figure 3(a) In electrodes with low aspect ratios, uric acid diffusion exhibits one-dimensional diffusion (linear diffusion), therefore the diffusion layer 214 becomes a semi-oblong shape (semi-elliptical shape) (see reference). Figure 3 (b)). It should be noted that, Figure 3 (a) and Figure 3 The arrows in (b) schematically represent the diffusion of uric acid caused by applying a specified voltage. Thus, in high aspect ratio electrodes, spherical diffusion (two-dimensional diffusion, three-dimensional diffusion) predominates over linear diffusion, resulting in a higher current density (current per unit area of ​​working electrode 21) generated by the redox reaction of uric acid on the electrode surface compared to low aspect ratio electrodes. Furthermore, the effect of IR drop is smaller in high aspect ratio electrodes than in low aspect ratio electrodes. IR drop refers to the voltage drop caused by the current flowing between working electrode 21 and counter electrode 22 due to the solution resistance between working electrode 21 and reference electrode 23. In high aspect ratio electrodes, the resistance between the electrode and liquid interface increases, thereby reducing the ratio of solution resistance to the overall system resistance. Consequently, the effect of IR drop is smaller. The higher the aspect ratio of working electrode 21, the higher the aforementioned current density, and the lower the effect of IR drop, resulting in higher sensing sensitivity.

[0071] By making the thickness of the support 212 350 μm or more, for example, the working electrode 21 becomes an electrode in which uric acid diffuses in a manner that can be considered as spherical diffusion when a specified voltage is applied. That is, the working electrode 21 becomes an electrode with a high aspect ratio. As a result, the sensing sensitivity can be improved. It should be noted that, from the viewpoint of making the working electrode 21 an electrode with a high aspect ratio, it is preferable that the thickness of the support 212 is as thick as possible. Currently, the thickness of silicon substrates commonly available on the market is about 775 μm in a 12-inch single-crystal Si substrate, so the maximum thickness of the support 212 is about 775 μm.

[0072] The working electrode 21 is rectangular, for example, square, when viewed from above. That is, the working electrode 21 is formed in a chip shape. The planar area of ​​the working electrode 21 can be set to, for example, 25 mm². 2 Therefore, a high aspect ratio working electrode 21 can be easily obtained. With a constant thickness of the support 212, the smaller the planar area of ​​the working electrode 21, the higher the aspect ratio of the working electrode 21 becomes. Therefore, from the viewpoint of obtaining a high aspect ratio working electrode 21, it is preferable that the planar area of ​​the working electrode 21 be as small as possible. Furthermore, the smaller the planar area of ​​the working electrode 21, the greater the resistance between the electrode and the liquid interface, which can further reduce the ratio of solution resistance to the overall system resistance. As a result, the influence of IR drop can also be reliably reduced. However, from the viewpoint of fabricating a chip-shaped working electrode 21, it is preferable that the planar area of ​​the working electrode 21 be, for example, 1 mm². 2That's all. If the area is a plane, it's 1 mm². 2 The working electrode 21 described above can be manufactured with high precision, stability, and ease using the fracture method described later. Furthermore, the planar area of ​​the working electrode 21 is 1 mm². 2 In addition, it can also suppress the reduction in the processability of the working electrode 21 and the reduction in installation stability.

[0073] (3) Manufacturing method of electrochemical sensor

[0074] Main reference Figure 4 and Figure 5 The manufacturing method of the sensor 100 of this embodiment will be described.

[0075] In the manufacturing method of the sensor 100 of this embodiment, the following is performed:

[0076] The steps for fabricating the working electrode 21 (step A); and

[0077] Step B is the step of placing the working electrode 21 on the substrate 10.

[0078] It should be noted that in step A, as the working electrode 21, an electrode in the shape of a chip with a diamond film 211 and a support 212 is made. When a specified voltage is applied between the working electrode 21 and the counter electrode 22, an oxidation-reduction reaction occurs on the surface of the diamond film 211. The support 212 is formed of a material other than diamond and supports the diamond film 211.

[0079] In addition, in step B, the working electrode 21 is disposed on the substrate 10 with the support 212 located on the substrate 10 side, and the working electrode 21 is mounted on the substrate 10 with at least a portion of the side of the support 212 exposed.

[0080] Furthermore, after step B, a step (step C) is performed to deactivate the sides of the support 212. In step C, for example, the substrate 10 on which the working electrode 21 is provided is annealed in an oxygen (O) atmosphere or a nitrogen (N) atmosphere, or the substrate 10 on which the working electrode 21 is provided is irradiated with ultraviolet light in an O atmosphere to deactivate the sides of the support 212. In step C, the substrate 10 on which the working electrode 21 is provided may also be placed in a clean atmosphere to deactivate the sides of the support 212.

[0081] (Step A)

[0082] In this step, a working electrode 21 with a diamond film 211 and a support 212 is fabricated.

[0083] Specifically, first, a support 212 made of a material other than diamond is prepared. For example, a support with a circular shape when viewed from above and containing conductive silicon (Si) is prepared; preferably, a support 212 with conductivity and low resistance (e.g., a silicon substrate) is prepared. Then, a seeding treatment, scratch treatment, etc., is performed on either of the two main surfaces of the support 212. Hereinafter, the surface on which the seeding treatment, scratch treatment, etc., is performed, that is, the surface on which the diamond film 211 is grown, will be referred to as the "upper surface of the support 212". Here, the seeding treatment refers to, for example, a process in which diamond particles (preferably diamond nanoparticles) of about several nm to tens of μm are coated onto the upper surface of the support 212, or the support 212 is immersed in the dispersion, thereby causing the diamond particles to adhere to the upper surface of the support 212. Scratch treatment refers to the process of applying scratches to the upper surface of the support 212 using diamond abrasive grains (diamond powder) of about a few μm. This allows a diamond film 211 to grow on the upper surface of the support 212.

[0084] After the support 212 is subjected to seeding treatment, scratch treatment, etc., a diamond film 211 is grown on the upper surface of the support 212, for example, by using a hot filament CVD method with tungsten wire.

[0085] The growth of diamond film 211 can be, for example, by using Figure 4The hot-filament CVD apparatus 300 shown is used for this process. The hot-filament CVD apparatus 300 is made of heat-resistant materials such as quartz and includes an airtight container 303 with a growth chamber 301 inside. A base 308 for holding a support 212 is provided inside the growth chamber 301. Connected to the side wall of the airtight container 303 are: a gas supply pipe 332a for supplying nitrogen (N2) gas to the growth chamber 301; a gas supply pipe 332b for supplying hydrogen (H2) gas; a gas supply pipe 332c for supplying methane (CH4) gas or ethane (C2H6) gas, which are carbon (C) gases; and a gas supply pipe 332d for supplying trimethylboron (B(CH3)3, abbreviated as TMB) gas, trimethyl borate (B(OCH3)3) gas, triethyl borate (B(C2H5O)3) gas, or diborane (B2H6) gas, which are boron (B) gases. Flow controllers 341a-341d and valves 343a-343d are sequentially installed on gas supply pipes 332a-332d, starting from the upstream side of the gas flow. Nozzles 349a-349d, which supply the gases from gas supply pipes 332a-332d to the growth chamber 301, are connected to the downstream ends of gas supply pipes 332a-332d. An exhaust pipe 330 for venting gas from the growth chamber 301 is installed on the other side wall of the airtight container 303. A pump 331 is installed on the exhaust pipe 330. A temperature sensor 309 for measuring the temperature inside the growth chamber 301 is installed inside the airtight container 303. Additionally, a tungsten wire 310 and a pair of electrodes (e.g., molybdenum (Mo) electrodes) 311a and 311b for heating the tungsten wire 310 are installed inside the airtight container 303. Each component of the hot filament CVD apparatus 300 is connected to a controller 380 configured as a computer, and is configured to control the processing steps and processing conditions described later by a program executed on the controller 380.

[0086] The growth of diamond film 211 can be carried out using the hot filament CVD apparatus described above, through the following processing steps. First, the support 212 is placed (moved) into the airtight container 303 and held on the base 308. Then, while venting the growth chamber 301, H2 gas is supplied into the growth chamber 301. Additionally, current is flowed between electrodes 311a and 311b to begin heating the tungsten filament 310. As the tungsten filament 310 is heated, the support 212 held on the base 308 is also heated. If the tungsten filament 310 reaches the desired temperature, the growth chamber 301 reaches the desired growth pressure, and the atmosphere in the growth chamber 301 becomes the desired atmosphere, a C-containing gas (e.g., CH4 gas) and a B-containing gas (e.g., TMB gas) are supplied into the growth chamber 301. The CH4 gas and TMB gas supplied into the growth chamber 301 decompose (thermally decompose) when passing through the tungsten filament 310 heated to a high temperature, generating methyl radicals (CH3). *Active species such as ) are supplied to the support 212 to grow a diamond film.

[0087] The following conditions are examples of the conditions for growing the diamond film 211. It should be noted that the growth time of the diamond film 211 is adjusted appropriately according to the thickness of the diamond film 211.

[0088] Substrate temperature: 600°C or higher and 1000°C or lower, preferably 650°C or higher and 800°C or lower.

[0089] Wire temperature: 1800℃ or higher and 2500℃ or lower, preferably 2000℃ or higher and 2200℃ or lower.

[0090] Growth chamber pressure: 5 Torr or higher and 50 Torr or lower, preferably 10 Torr or higher and 35 Torr or lower.

[0091] The ratio of the partial pressure of TMB gas to CH4 gas (TMB / CH4): greater than 0.003% and less than 0.8%.

[0092] The ratio of CH4 gas to H2 gas (CH4 / H2): 2% to 5%

[0093] Therefore, production Figure 5 (a) A cross-sectional schematic diagram showing a laminate 220 of the support 212 and the diamond film 211. It should be noted that since the diamond film 211 is grown on the support 212, which is made of a material other than diamond, the grown diamond film 211 becomes a polycrystalline diamond film or a DLC film. Furthermore, by growing the diamond film 211 under the above conditions, the B concentration in the diamond film 211 becomes, for example, 1 × 10⁻⁶. 19 cm -3 Above and 1×10 22 cm -3 the following.

[0094] After the growth of diamond film 211 is completed, as follows Figure 5As shown in (b), a recessed groove 221 (e.g., a scribing groove) is formed from the back side of the laminate 220 (the side opposite to the upper surface of the support 212). The recessed groove 221 can be formed using known methods such as laser scribing, laser cutting, mechanical processing, or etching. The recessed groove 221 is preferably formed so that it does not penetrate the support 212 in the thickness direction, i.e., it does not reach the diamond film 211. It is preferable to form the recessed groove 221 such that the thickness of the thinnest part of the support 212 is, for example, 10 μm or more and 80 μm or less. By providing the recessed groove 221 in this way, the reduction in fracture control of the diamond film 211 can be suppressed, and the deterioration of the diamond film 211 can be suppressed. By suppressing the deterioration of the diamond film 211, the reduction in sensing sensitivity can be suppressed. It should be noted that the deterioration of the diamond film 211 refers to, for example, the degradation of the sp in the diamond film 211. 3 The key becomes sp 2 Bonds, such as graphitization.

[0095] Next, as Figure 5 As shown in (c), the diamond film 211 is broken along the concave groove 221. Preferably, the diamond film 211 is bent outwards along the concave groove 221 to cause the breakage. This results in a working electrode 21 with a chip shape having a diamond film 211 and a support 212.

[0096] It should be noted that it is also possible to form a concave groove 221 from the surface side (diamond film 211 side) of the laminate 220. However, the diamond film 211 is very hard (high hardness), so it is difficult to form a concave groove 221 from the diamond film 211 side by laser processing, machining or other methods.

[0097] Alternatively, it is also considered to obtain the working electrode 21 by shaping the laminate 220 into a predetermined shape using dry etching or the like. However, it is very difficult to shape the laminate 220 with a high-hardness diamond film 211 into a predetermined shape using dry etching or the like. In addition, if dry etching is performed, altered regions sometimes occur in the diamond film 211.

[0098] In contrast, as described above, by forming a concave groove 221 from the back side of the support 212 and breaking the diamond film 211 along the concave groove 221, it is possible to easily fabricate a working electrode 21 of a predetermined shape (chip shape) even with a diamond film 211 having high hardness. Furthermore, since etching or the like is not performed, no deterioration region is generated in the diamond film 211, thus suppressing the degradation of the diamond film 211's quality and the reduction in sensor performance of the sensor 100.

[0099] The support 212 of the working electrode 21, obtained by forming a concave groove 221 and fracturing the diamond film 211 along the concave groove 221, has at least one of a scribing surface or an etched surface formed by forming the concave groove 221, and a fracture surface formed when the diamond film 211 is fractured. The fracture surface formed when the diamond film 211 is fractured. The term "scribing surface" here refers to a surface including, for example, a molten surface (laser-processed surface) formed by laser scribing (laser processing), or a cutting surface (machined surface) formed by scribing (machining) using a diamond scribing tool, etc. The term "etched surface" here refers to a surface formed by wet etching or etching using plasma or ion beams. The term "fracture surface" here sometimes includes a cleaved surface.

[0100] (Step B)

[0101] After step A is completed, proceed to step B.

[0102] In this step, firstly, a substrate 10 is prepared, and wiring 31 to 33, for example, made of Au, is formed on the upper surface of the substrate 10. For example, a substrate 10 with a gold film (Au film) pre-attached to any main surface is prepared, a resist with a predetermined pattern is formed on the Au film, and then the Au film (i.e., the unwanted parts of the Au film) not covered by the resist is removed by etching or the like. Thus, a predetermined conductor pattern, which becomes wiring 31 to 33, is formed on the substrate 10. It should be noted that, in addition to Au, wiring 31 to 33 can also be formed using various noble metals such as Cu, Pt, Ag, or Pd, various metals such as Al, Fe, Ni, Cr, and Ti, alloys with these noble metals or metals as the main components, oxides of the above noble metals or alloys, metal oxides, etc., as described above. In addition, when forming wiring 31 to 33, counter electrode 22 integral with wiring 32 is also formed simultaneously.

[0103] Next, an Ag / AgCl electrode is formed as the reference electrode 23. For example, a silver wire or silver plate is placed at a predetermined position on the wiring 33 made of Au, and molten AgCl is coated onto the silver wire or silver plate to form the Ag / AgCl electrode. It should be noted that the reference electrode 23, such as the Ag / AgCl electrode, which is separate from the pre-fabricated wiring 33, can also be provided on the upper surface of the substrate 10 via the same conductive adhesive as the conductive adhesive 14. In this case, a predetermined amount of conductive adhesive is applied in such a way that the reference electrode 23 is electrically connected to the wiring 33 via the conductive adhesive. It should be noted that the exposed Au portion of the wiring 33 can also be used directly as the reference electrode 23 without forming an Ag / AgCl electrode.

[0104] Next, the working electrode 21 is disposed (mounted) on the upper surface of the substrate 10 with the support 212 located on the side of the substrate 10 via a conductive adhesive 14. At this time, a predetermined amount of conductive adhesive 14 is applied so that the working electrode 21 and the wiring 31 are electrically connected via the conductive adhesive 14. Then, the conductive adhesive 14 is cured (curing process).

[0105] Next, the exposed wiring 31 and conductive adhesive 14 are covered with insulating material 15. The insulating material 15 is configured to prevent the wiring 31 and conductive adhesive 14 from being exposed, while exposing at least a portion of the side of the working electrode 21 (support 212). Preferably, the insulating material 15 is used to cover the conductive adhesive, wiring 32, 33, which electrically connects the reference electrode 23 to the wiring 33, so that these are also not exposed.

[0106] (Step C)

[0107] After step B is completed, proceed to step C.

[0108] In this step, with at least a portion of the side of the support 212 exposed, the substrate 10 on which the working electrode 21 is provided is annealed in an atmosphere containing O or N.

[0109] The following conditions can be cited as examples of annealing conditions.

[0110] Annealing atmosphere: O2 gas, atmosphere or N2 gas

[0111] Annealing temperature: 60℃ or higher and 200℃ or lower, preferably 70℃ or higher and 140℃ or lower.

[0112] Annealing time: 5 minutes or more but less than 180 minutes, preferably 60 minutes or more but less than 120 minutes.

[0113] By annealing under the above conditions, a thermal oxide film (SiO2) serving as an insulating film 213 can be formed on the entire side of the support 212. x A film or nitride film (SiN film) can deactivate at least the surface portion of the side surfaces (i.e., the scribing or etched surfaces, and the fracture surfaces) of the support 212.

[0114] In this step, the substrate 10, on which the working electrode 21 is provided, can be irradiated with ultraviolet light, for example, using a mercury lamp in an O atmosphere, with at least a portion of the side of the support 212 exposed, instead of the annealing described above.

[0115] The following conditions can be cited as examples of conditions for exposure to ultraviolet light.

[0116] Irradiation atmosphere: O2 gas or atmosphere

[0117] Irradiation temperature: room temperature (25-28°C, e.g., 27°C)

[0118] Irradiation time: 5 minutes or more but less than 30 minutes, preferably 10 minutes or more but less than 20 minutes.

[0119] By irradiating the support with ultraviolet light under the above conditions, an ozone oxide film as an insulating film 213 can be formed on the entire side of the support 212, thereby deactivating the surface layer of the side of the support 212.

[0120] Alternatively, in this step, the substrate 10, on which the working electrode 21 is provided, can be placed in a clean atmosphere, such as a clean bench, with at least a portion of the side of the support 212 exposed, to form a natural oxide film, instead of the annealing or ultraviolet irradiation described above.

[0121] The following conditions can be cited as examples of conditions for the formation of a natural oxide film.

[0122] Atmosphere in which natural oxide film forms: Atmosphere with humidity above 50%.

[0123] Natural oxide film formation temperature: above room temperature (25℃)

[0124] Natural oxide film formation time: over 1000 minutes

[0125] By placing the substrate 10, on which the working electrode 21 is provided, in the atmosphere under the above conditions, a natural oxide film serving as an insulating film 213 can be formed on the entire side of the support 212, thereby deactivating the side of the support 212. However, from the viewpoint that the insulating film 213 can reliably become a continuous film and that the insulating film 213 can reliably cover the entire side of the support 212, the above-mentioned annealing or ultraviolet irradiation is preferred.

[0126] It should be noted that by deactivating the sides of the support 212 under the above conditions, the wiring 31-33 is oxidized or nitrided. However, under the annealing conditions, ultraviolet irradiation conditions, and natural oxide film formation conditions in this step, only the surface (surface layer) of the wiring 31-33 is oxidized or nitrided, so it has almost no effect on the conductivity of the wiring 31-33.

[0127] Furthermore, by performing this step (step C) after step B is completed, specifically after the working electrode 21 and the wiring 31 are electrically connected via the conductive adhesive 14, it is possible to reliably prevent accidental oxidation of parts due to annealing or the like, thereby preventing the electrical connection between the working electrode 21 and the wiring 31 from being severed.

[0128] It should be noted that even without intentionally performing step C, a natural oxide film is formed on the side surface of the support 212. However, this natural oxide film is mostly not a continuous film, so without performing step C, the inactivation of the side surface of the support 212 is insufficient. By performing step C, the entire side surface of the support 212 can be sufficiently inactivated, and the entire side surface of the support 212 can be covered with an insulating film 213.

[0129] (4) Method for determining uric acid concentration using an electrochemical sensor

[0130] A method for measuring the concentration of uric acid in urine by electrochemical measurement using the sensor 100 described above will be explained.

[0131] In the method for determining uric acid concentration using sensor 100, the following is implemented:

[0132] The step of connecting the measuring mechanism to the sensor 100 (Step 1);

[0133] Step 2: Supplying the test sample to the sensor 100 and supplying (attaching) the test sample to the electrode assembly 20;

[0134] Step 3: With the test sample in contact with the surface of the electrode assembly 20, a voltage is applied between the working electrode 21 and the counter electrode 22, and a redox reaction of uric acid occurs on the surface of the diamond film 211 on the working electrode 21, and the current value flowing through the redox reaction of uric acid is measured.

[0135] Step 4 involves measuring the potential difference (voltage difference) between the working electrode 21 and the reference electrode 23 while the test sample is in contact with the surface of the electrode assembly 20; and

[0136] Step 5: Quantifying uric acid concentration based on measured current value and potential difference.

[0137] (Step 1)

[0138] In this step, the measuring mechanism is connected to the sensor 100. Specifically, the ends of the wirings 31-33 of the sensor 100 opposite to the side connected to the working electrode 21, counter electrode 22, and reference electrode 23 are exposed, and the connecting part of the measuring mechanism is connected to these exposed ends. A known potentiostat or a similar circuit can be used as the measuring mechanism. The measuring mechanism includes, for example, a voltage application section, a current measurement section, a potential difference measurement section, and a potential adjustment section. The voltage application section is configured to apply a voltage between the working electrode 21 and the counter electrode 22 when the connecting part is connected to the wirings 31-33 to form a predetermined circuit. The current measurement section is configured to measure the current generated by the redox reaction of uric acid. The potential difference measurement section is configured to measure the potential difference between the working electrode 21 and the reference electrode 23. The potential adjustment section is configured to maintain the potential of the working electrode 21 at a constant level based on the potential difference measured by the potential difference measurement section and using the potential of the reference electrode 23 as a reference.

[0139] (Step 2)

[0140] After connecting the measuring mechanism to the sensor 100, the test sample is supplied to the sensor 100 so that the test sample is attached to the electrode assembly 20.

[0141] (Step 3)

[0142] With the test sample attached to the surface of the electrode assembly 20, a predetermined voltage is applied between the working electrode 21 and the counter electrode 22 by the voltage application unit of the measuring mechanism, thereby causing a redox reaction of uric acid on the surface of the diamond film 211 of the working electrode 21. Due to the uric acid redox reaction, a current (reaction current) flows within the working electrode 21. The value of this reaction current is measured using a measuring mechanism, for example, by cyclic voltammetry. Examples of cyclic voltammetry conditions include a voltage range of 0V to 1V and a scan rate of 0.1V / s to 1V / s. The value of the reaction current can be measured using methods such as square wave voltammetry (rectangular voltammetry), differential pulse voltammetry, normal pulse voltammetry, and alternating current voltammetry.

[0143] (Step 4)

[0144] With the test sample in contact with the surface of the electrode assembly 20, the potential difference between the working electrode 21 and the reference electrode 23 is measured by the potential difference measuring unit of the measuring mechanism.

[0145] (Step 5)

[0146] Based on the value of the reaction current measured in step 3, a cyclic voltammogram is prepared to obtain the current value of the oxidation peak. Based on the obtained oxidation peak current value and the potential difference measured in step 4, the uric acid concentration in the test sample is calculated (quantified). The inventors of this application have confirmed a correlation between the value of the reaction current and the concentration of uric acid in urine. Therefore, if the relationship between the value of the reaction current and the uric acid concentration is determined in advance, the uric acid concentration can be quantified based on the measured value of the reaction current.

[0147] (5) Effects obtained through this implementation method

[0148] According to this embodiment, one or more of the following effects can be obtained.

[0149] (a) In this embodiment, the working electrode 21 is mounted on the substrate 10 with at least a portion of the side surface of the support 212 exposed. Even with this simple structure of mounting the working electrode 21 on the substrate 10 with at least a portion of the side surface of the support 212 exposed, the sensor 100 can accurately measure the uric acid concentration in the test sample. That is, even with such a simple structure, the sensor 100 can accurately perform sensing.

[0150] The inventors of this application have confirmed that even with at least a portion of the side of the support 212 exposed, the concentration of uric acid in a test sample containing uric acid can be accurately measured. For example, Figure 6 As shown in the cyclic voltammetry diagrams (a) to (c), the oxidation current peak (oxidation peak) of uric acid can be clearly observed. Furthermore, the inventors of this application used a solution with a previously known uric acid concentration (an aqueous solution in which a specified amount of uric acid is dissolved in water) and measured the uric acid concentration in the aqueous solution using sensor 100 via cyclic voltammetry. The results confirmed that the uric acid concentration measured using sensor 100 was consistent with the uric acid concentration in the aqueous solution.

[0151] (b) The working electrode 21 is mounted on the substrate 10 with the side of the support 212 exposed, thereby improving the sensing sensitivity. In addition, by increasing the exposed area of ​​the side of the support 212, the sensing sensitivity of the sensor 100 can be further improved.

[0152] Here, Figure 6 Sample 1 shown in (a) Figure 6 (b) Sample 2 Figure 6 (c) The exposed areas of the sides of the supports 212 of each of the samples 3 are different. In sample 1, as shown... Figure 7 As shown in (a), a significant portion of the side surface of the support 212 is covered by the insulating material 15, meaning that the exposed area of ​​the side surface of the support 212 is relatively small. In sample 2, as... Figure 7 As shown in (b), the exposed area on the side of the support is greater than that in sample 1. In sample 3, as... Figure 7 As shown in (c), the exposed area of ​​the side surface of support 212 is greater than that of samples 1 and 2. That is, the exposed area of ​​the side surface of support 212 decreases in the order of sample 3, sample 2, and sample 1. (Comparison) Figure 6 As shown in (a) to (c), the more exposed area on the side of the support 212, the higher the current value of the oxidation peak observed in the cyclic voltammogram near the applied voltage of 0.5V. Therefore, the more exposed area on the side of the support 212, the higher the sensing sensitivity.

[0153] It should be noted that when the working electrode 21 is not installed with the side of the support 212 exposed, that is, when the entire side of the support 212 is covered with insulating material 15, the sensing sensitivity is reduced. This is because the thickness of the diamond film 211 is very thin compared to the thickness of the support 212. Therefore, if the insulating material 15 is provided to cover the entire side of the support 212 without exposing it, in most cases, the insulating material 15 will overflow onto the surface (upper surface) of the diamond film 211. As a result, the area of ​​the diamond film 211 that is helpful for sensing is reduced, resulting in a decrease in sensing sensitivity. In addition, when the entire side of the support 212 is covered with insulating material 15, the effect of setting the working electrode 21 as an electrode with a high aspect ratio is sometimes reduced. That is, the diffusion, which is considered as spherical diffusion, is sometimes reduced. In addition, it is sometimes difficult to obtain the effect of reducing the influence of IR drop. As a result, the sensing sensitivity is reduced.

[0154] (c) By performing a treatment to deactivate the sides of the support 212, the insulating film 213 can be reliably made into a continuous film, and the insulating film 213 can reliably cover the entire side of the support 212. That is, the side of the support 212 can be sufficiently deactivated. As a result, even when a test sample is attached to the side of the support 212, the redox reaction of uric acid on the side of the support 212 when a specified voltage is applied can be reliably suppressed. That is, a working electrode 21 can be obtained where a redox reaction occurs on the surface of the diamond film 211 when a specified voltage is applied, but no redox reaction occurs on the side of the support 212. As a result, the concentration of uric acid in the test sample can be measured more accurately.

[0155] exist Figure 8 The diagram shows cyclic voltammograms of samples that have undergone sufficient inactivation treatment and samples that have not undergone sufficient inactivation treatment. (See diagram for reference.) Figure 8As shown, when the deactivation treatment is insufficient, the current value of the oxidation peak is lower compared with that when the deactivation treatment is sufficient, and sometimes the oxidation peak does not appear clearly.

[0156] (d) Since the working electrode 21 is chip-shaped, it is easy to mount on the substrate 10. Therefore, the mass production of the sensor 100 using the working electrode 21 with a high-hardness diamond film 211 can be improved.

[0157] (e) By making the resistivity of the support 212 below 0.04 Ωcm, the external resistance in the reaction current flow path can be reduced, thereby minimizing the variation in the value of the reaction current caused by the external resistance. As a result, the concentration of uric acid in the test sample can be determined more accurately.

[0158] (f) By making the resistivity of the support 212 below 0.04 Ωcm, the carrier concentration in the support 212 can be, for example, 1 × 10⁻⁶. 18 cm -3 Therefore, the connection resistance between the back surface of the support 212 and the metal component in the conductive adhesive 14 can be made less than 10% of the liquid-interface resistance. Thus, fluctuations in the reaction current value caused by external resistance can be reliably reduced. Furthermore, the addition of external resistance components to the reaction current curve on the cyclic voltammogram obtained by cyclic voltammetry can be suppressed, resulting in a smaller peak current value. These results enable more accurate determination of the uric acid concentration in the test sample.

[0159] (g) By having a support 212 with a thickness of 350 μm or more, the working electrode 21 can be configured as an electrode in which uric acid diffuses in a manner that can be considered as spherical diffusion when a specified voltage is applied, i.e., an electrode with a high aspect ratio. As a result, the current density generated by the redox reaction of uric acid on the surface of the working electrode 21 can be increased, and the influence of IR drop can be reduced, thereby improving the sensing sensitivity.

[0160] (h) By making the thickness of the support 212 350 μm or more, 6-inch and 8-inch commercially available single-crystal Si substrates, polycrystalline Si substrates, etc., can be directly used as the support 212 without the need for back rap to adjust the thickness. As a result, the productivity of the working electrode 21 can be improved and the manufacturing cost can be reduced.

[0161] (i) The planar area of ​​the working electrode 21 is 25 mm². 2 Therefore, it is easier to obtain a working electrode 21 with a high aspect ratio. As a result, the sensing sensitivity can be reliably improved.

[0162] (j) By electrically connecting the working electrode 21 to the wiring 31 via a conductive adhesive 14 instead of using wire bonding or the like in the past, it is easy to electrically connect the working electrode 21 to the wiring 31 even if the planar area of ​​the working electrode 21 is small. In addition, compared with the case of connection using wire bonding or the like, the mass production of the sensor 100 can be improved.

[0163] Here, for reference, a conventional working electrode with a diamond film will be described. A conventional working electrode with a diamond film, for example, is fabricated by preparing a substrate (circuit board) with an opening, and attaching a diamond film from the back side of the substrate to block the opening. In such a working electrode, a diamond film with a planar area larger than the planar area of ​​the opening is required. In such a working electrode, in addition to the area that contributes to electrochemical measurement (sensing) (the area exposed from the opening), excess diamond film that does not contribute to sensing is required, thus sometimes increasing manufacturing costs. Furthermore, it is sometimes impossible to miniaturize the working electrode, making it difficult to miniaturize the electrochemical sensor. It should be noted that when miniaturizing such a working electrode, the thickness of the substrate becomes relatively excessive relative to the area of ​​the opening, thus the diffusion of uric acid exhibits linear diffusion.

[0164] Furthermore, as a small working electrode with a diamond film, a needle-shaped electrode formed from diamond has been proposed. The needle-shaped electrode can be fabricated by vapor-depositing a diamond film onto the tip of a metal needle. Alternatively, a needle-shaped electrode can be fabricated by preparing a diamond substrate and forming a needle-like protrusion arrangement on the surface of the diamond substrate using methods such as dry etching with oxygen. However, the fabrication process of these working electrodes is more complex than that of a chip-shaped working electrode with a diamond film, as in this invention. Additionally, if the diamond substrate is dry-etched, the diamond substrate in the etched area and its surrounding area may sometimes deteriorate. It should be noted that when the surface of the diamond substrate is treated by laser irradiation, plasma irradiation, ion beam irradiation, etc., the diamond substrate may sometimes deteriorate, similar to when the surface of the diamond substrate is treated by dry etching. In working electrodes using diamond substrates with such deteriorated areas, the accuracy of electrochemical measurements may sometimes decrease.

[0165] <Other Implementation Methods>

[0166] The embodiments of the present invention have been described above in detail. However, the present invention is not limited to the embodiments described above, and various modifications can be made without departing from its spirit.

[0167] In the above embodiments, examples of deactivating the sides of the support 212 by performing any of the above-described annealing, ultraviolet light irradiation, or placement in a clean atmosphere in step C have been described, but this is not a limitation. That is, various other methods can be used to perform the deactivation treatment as long as the sides of the support 212 can be deactivated. For example, instead of the above-described annealing, ultraviolet light irradiation, or placement in a clean atmosphere, various acids, aqueous solutions of hydrogen peroxide, water, etc., can be used to deactivate the sides of the support 212. As such a method, immersion in oxygen-containing pure water or a solution containing an oxidant for chemical etching to deactivate the sides of the support 212 is considered.

[0168] In the above-described embodiments and other embodiments, examples of deactivating the sides of the support 212 by performing any of the above-described annealing, ultraviolet light irradiation, placement in a clean atmosphere, or chemical etching in step C have been described, but the method is not limited thereto. Multiple methods described above for deactivating the sides of the support 212 may also be appropriately combined.

[0169] In the above embodiment, step C was described as an example where the working electrode 21, counter electrode 22, reference electrode 23, and wiring 31-33 were provided on the upper surface of the substrate 10, but this is not a limitation. As long as the working electrode 21 and wiring 31 are provided on the upper surface of the substrate 10, and the working electrode 21 and wiring 31 are electrically connected via conductive adhesive 14, step C can be performed before the counter electrode 22, reference electrode 23, and wiring 32, 33 are provided on the upper surface of the substrate 10. Even in this case, the side surface (the entire surface) of the support 212 can be covered with an insulating film 213, which can sufficiently deactivate the side surface of the support 212. As a result, the above-mentioned uric acid redox reaction inhibition effect can be obtained.

[0170] In the above embodiments, an example was described where the conductive adhesive 14 and wiring 31 were covered with insulating material 15 to prevent them from being exposed, but this is not a limitation. If other means are taken to suppress the exposure of the conductive adhesive 14 and wiring 31, the conductive adhesive 14 and wiring 31 do not necessarily need to be covered with insulating material 15. That is, in such cases, insulating material 15 may not be provided.

[0171] In the above embodiments, an example of determining the concentration of uric acid in a liquid test sample containing uric acid has been described, but the method is not limited to this. Besides urine from humans and animals, other liquid test samples containing uric acid can also be human and animal blood, tears, nasal mucus, saliva, sweat, etc. Furthermore, the detected component can be other than uric acid. If the voltage applied between the working electrode 21 and the counter electrode 22 is within a specified range, the concentration of various components (substances) in the liquid test sample can be determined by appropriately changing the conditions of the cyclic voltammetry.

[0172] Alternatively, a specified enzyme corresponding to the detected component can be coated on the diamond film 211, allowing the detected component, such as uric acid, to undergo an electrochemical reaction with the enzyme to calculate the concentration of the detected component.

[0173] In the above embodiments, an example of determining the concentration of a specified component in a liquid test sample using a three-electrode method has been described, but the method is not limited to this. For example, the concentration of a specified component in a liquid test sample can also be determined using a two-electrode method. In this case, the sensor 100 can be configured in the same way as in the above embodiments, except that the reference electrode 23 and wiring 33 are not provided.

[0174] In the above embodiment, an example of a sensor 100 having one electrode group 20 has been described, but the sensor 100 may also have multiple electrode groups 20. In the case of multiple electrode groups 20, wiring 31 to 33 is connected to each electrode respectively.

[0175] <Preferred embodiments of the present invention>

[0176] The preferred embodiments of the present invention are described below.

[0177] (Postscript 1)

[0178] According to one aspect of the present invention, an electrochemical sensor is provided, comprising:

[0179] Working electrode;

[0180] counter electrode; and

[0181] The substrate supports the working electrode and the counter electrode.

[0182] The aforementioned working electrode is a chip-shaped electrode having a diamond film and a support. When a predetermined voltage is applied between the working electrode and the aforementioned counter electrode with a test sample (electrolyte), a redox reaction occurs on the surface of the aforementioned diamond film. The aforementioned support is formed of a material other than diamond and supports the aforementioned diamond film.

[0183] The working electrode is mounted on the substrate with the support located on the substrate side and at least a portion of the side of the support exposed.

[0184] (Postscript 2)

[0185] According to the sensor described in Appendix 1, the working electrode is preferably configured such that when a predetermined voltage is applied between the working electrode and the counter electrode while a test sample is present, a redox reaction occurs on the surface of the diamond film, but no redox reaction occurs on the side surface of the support. That is, the side surface of the support is deactivated.

[0186] (Note 3)

[0187] According to the sensor described in Appendix 1 or 2, it is preferable to form an insulating film on the side of the support. That is, the inactivation of the side of the support is achieved by forming an insulating film on the side of the support.

[0188] (Note 4)

[0189] According to any one of the appendices 1 to 3, the sensor preferably supplies (attaches) a liquid containing uric acid as a test sample to the working electrode and the counter electrode, and the redox reaction of the uric acid in the liquid occurs on the surface of the diamond film.

[0190] (Note 5)

[0191] According to any one of Appendices 1 to 4, the support body is preferably made of a material with a resistivity of 0.04 Ωcm or less.

[0192] (Note 6)

[0193] According to any one of the appendices 1 to 5, the support body is preferably made of elemental silicon or a silicon compound.

[0194] (Note 7)

[0195] According to any one of Appendices 1 to 6, the support body is preferably composed of any one of a monocrystalline silicon substrate, a polycrystalline silicon substrate, or a silicon carbide substrate.

[0196] (Postscript 8)

[0197] According to any one of the appendices 3 to 7, the insulating film is preferably a continuous film with a thickness of 1 nm or more, covering the entire side of the support.

[0198] (Note 9)

[0199] According to any one of the appendices 1 to 8, the thickness of the support body is preferably 350 μm or more.

[0200] (Postscript 10)

[0201] According to any one of the appendices 1 to 9, the planar area of ​​the working electrode is preferably 25 mm². 2 the following.

[0202] (Postscript 11)

[0203] According to any one of the appendices 1 to 10, the working electrode is preferably mounted (bonded) to the substrate via a conductive adhesive.

[0204] (Postscript 12)

[0205] The sensor according to any one of Appendices 1 to 11 preferably further comprises wiring connected to the aforementioned working electrode.

[0206] The aforementioned wiring is supported on the aforementioned substrate.

[0207] The aforementioned working electrode and the aforementioned wiring are electrically connected via a conductive adhesive.

[0208] (Postscript 13)

[0209] According to another aspect of the present invention, a method for manufacturing an electrochemical sensor is provided, comprising:

[0210] The process of fabricating the working electrode; and

[0211] The process of setting the above-mentioned working electrode on the substrate.

[0212] In the above-described process of fabricating the working electrode, a chip-shaped electrode is fabricated as the working electrode. The chip-shaped electrode has a diamond film and a support. When a predetermined voltage is applied between the working electrode and the counter electrode disposed on the substrate with a test sample (electrolyte), a redox reaction occurs on the surface of the diamond film. The support is formed of a material other than diamond and supports the diamond film.

[0213] In the process of setting the working electrode on the substrate, the working electrode is mounted on the substrate such that the support is located on the substrate side and at least a portion of the side of the support is exposed.

[0214] (Postscript 14)

[0215] According to the method described in Appendix 13, it is preferable that after the step of setting the working electrode on the substrate, a step of deactivating the side surface of the support is also performed.

[0216] (Postscript 15)

[0217] According to the method described in Appendix 13, it is preferable that, in the process of deactivating the side surface of the support, the substrate on which the working electrode is disposed is annealed in an oxygen-containing atmosphere or a nitrogen-containing atmosphere.

[0218] (Postscript 16)

[0219] According to the method described in Appendix 13, it is preferable that, in the process of deactivating the side surface of the support, the substrate on which the working electrode is disposed is irradiated with ultraviolet light under an oxygen-containing atmosphere.

[0220] (Postscript 17)

[0221] According to the method described in Appendix 13, it is preferable that, in the process of deactivating the side surface of the support, the substrate on which the working electrode is provided is placed in the atmosphere at a specified temperature for a specified time.

[0222] (Postscript 18)

[0223] According to any one of Appendices 13 to 17, it is preferable that in the step of setting the working electrode on the substrate, the working electrode is mounted on the substrate by means of a conductive adhesive.

[0224] Explanation of reference numerals in the attached figures

[0225] 100 Electrochemical Sensors

[0226] 10 Substrate

[0227] 21 Working electrode

[0228] 211 Diamond film

[0229] 212 Support

[0230] 22 pairs of electrodes

Claims

1. An electrochemical sensor comprising: Working electrode; counter electrode; and A substrate that supports the working electrode and the counter electrode. The working electrode is a chip-shaped electrode with a diamond film and a support. When a predetermined voltage is applied between the working electrode and the counter electrode while a sample is being tested, a redox reaction occurs on the surface of the diamond film. The support is formed of elemental silicon or a conductive silicon compound and supports the diamond film. An insulating film, formed by deactivating the sides of the support, is formed on the entire side of the support. The surface of the support body that contacts the diamond film is not covered with the insulating film, and the diamond film is in direct contact with the support body. The electrode is configured such that the current generated by the redox reaction flows from the diamond film through the support body to the wiring disposed on the upper surface of the substrate. The working electrode is mounted on the substrate with the support located on the substrate side and at least a portion of the side of the support exposed.

2. The electrochemical sensor according to claim 1, wherein, The working electrode is configured such that when a predetermined voltage is applied between the working electrode and the counter electrode while a test sample is present, a redox reaction occurs on the surface of the diamond film, but no redox reaction occurs on the side of the support.

3. The electrochemical sensor according to claim 1 or 2, wherein, A liquid containing uric acid, serving as a test sample, is supplied to the working electrode and the counter electrode, where a redox reaction of the uric acid in the liquid occurs on the surface of the diamond film.

4. The electrochemical sensor according to claim 1 or 2, wherein, The support is made of a conductive material with a resistivity of less than 0.04 Ωcm.

5. The electrochemical sensor according to claim 1 or 2, wherein, The support is made of a silicon substrate.

6. The electrochemical sensor according to claim 1 or 2, wherein, The support is composed of any one of a single-crystal Si substrate, a polycrystalline Si substrate, or a silicon carbide substrate.

7. The electrochemical sensor according to claim 1 or 2, wherein, The thickness of the support is 350 μm or more.

8. The electrochemical sensor according to claim 1 or 2, wherein, The working electrode has a planar area of ​​25 mm². 2 the following.

9. The electrochemical sensor according to claim 1 or 2, wherein, The working electrode is mounted to the substrate via a conductive adhesive.

10. A method for manufacturing an electrochemical sensor, comprising: a working electrode, a counter electrode, and a substrate supporting the working electrode and the counter electrode, the method comprising: The process of fabricating a chip-shaped electrode as the working electrode includes the following configuration: the chip-shaped electrode has a diamond film and a support; the diamond film undergoes a redox reaction on its surface when a predetermined voltage is applied between the working electrode and the counter electrode under a test sample condition; the support is formed of elemental silicon or a conductive silicon compound and supports the diamond film; the diamond film is in direct contact with the support; and the current generated by the redox reaction flows from the diamond film through the support to wiring disposed on the upper surface of the substrate. The process of mounting the working electrode to the substrate such that the support is located on the substrate side and at least a portion of the side surface of the support is exposed. The process of forming an insulating film on the side surface of the support. After the step of setting the working electrode on the substrate, the step of forming the insulating film is performed. In the process of forming the insulating film, the insulating film is formed on the entire side surface of the support by deactivating the side surface of the support. The insulating coating is not formed on the surface of the support that contacts the diamond film.

11. The method for manufacturing an electrochemical sensor according to claim 10, wherein, The support is composed of any one of a single-crystal Si substrate, a polycrystalline Si substrate, or a silicon carbide substrate.

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