Electrode, biosensor, and method for manufacturing electrode

Abstract

A protective layer (5) is formed of an inorganic material, and one surface of an electrode (1) in the thickness direction includes the protective layer (5). In the measurement of the atomic composition by Auger electron spectroscopy on one surface of the electrode (1) in the thickness direction, the proportion of elements derived from the inorganic material is 30 atom% or less.

Description

Electrode, biosensor, and method for manufacturing an electrode

[0001] The present invention relates to an electrode, a biosensor, and a method for manufacturing an electrode, and more specifically, to an electrode, a biosensor equipped with the electrode, and a method for manufacturing the electrode.

[0002] Traditionally, carbon electrodes have been used as electrodes in biosensors. The conductive carbon layer of the carbon electrode is surface-treated to impart hydrophilicity.

[0003] As such an electrode, for example, an electrode comprising a substrate and a conductive carbon layer, wherein the water contact angle of the conductive carbon layer is 80 degrees or less, has been proposed (see, for example, Patent Document 1 below).

[0004] International Publication No. 2022-0711293

[0005] Depending on the application, such biosensors are required to maintain their hydrophilicity for extended periods.

[0006] The present invention provides an electrode that maintains high performance as an electrode while exhibiting excellent long-term retention of hydrophilicity, a biosensor equipped with the electrode, and a method for manufacturing the electrode.

[0007] [1] The present invention relates to an electrode comprising a substrate, a conductive carbon layer disposed on one side of the substrate in the thickness direction, and a hydrophilic protective layer covering one surface of the conductive carbon layer in the thickness direction, wherein the protective layer is made of an inorganic material, one surface of the electrode in the thickness direction includes the protective layer, and the proportion of elements derived from the inorganic material is 30 atomic percent or less in atomic composition measurement by Auger electron spectroscopy on the one surface of the electrode in the thickness direction.

[0008] The present invention [2] includes the electrode according to claim 1, wherein the water contact angle of one side in the thickness direction of the electrode is 80° or less.

[0009] The present invention [3] is characterized in that the protective layer partially covers one surface of the conductive carbon layer in the thickness direction, and one surface of the electrode in the thickness direction includes the electrode of [1], which includes the conductive carbon layer and the protective layer.

[0010] The present invention [4] includes the electrode described in [1] above, wherein the element derived from the inorganic material includes silicon.

[0011] The present invention [5] includes a biosensor comprising the electrode described in any one of the above items [1] to [4].

[0012] The present invention [6] is a method for manufacturing an electrode according to any one of the above [1] to [4], comprising: a preparation step of preparing a substrate; a conductive carbon layer placement step of arranging a conductive carbon layer on one side in the thickness direction of the substrate; and a protective layer placement step of arranging a protective layer that covers the conductive carbon layer on one side in the thickness direction of the conductive carbon layer.

[0013] In the electrode of the present invention, one surface of the electrode in the thickness direction includes a hydrophilic protective layer. Furthermore, in the aforementioned surface of the electrode in the thickness direction, the proportion of elements derived from the inorganic material of the protective layer is 30 atomic percent or less, as measured by Auger electron spectroscopy. Therefore, hydrophilicity can be maintained for a long period of time while maintaining high performance as an electrode.

[0014] The biosensor of the present invention is equipped with the electrode of the present invention. Therefore, it can maintain high performance as an electrode while retaining hydrophilicity for a long period of time.

[0015] The electrode manufacturing method of the present invention can produce electrodes that maintain high performance as electrodes while also exhibiting excellent long-term retention of hydrophilicity.

[0016] Figure 1 is a schematic cross-sectional view of one embodiment of the electrode of the present invention. Figures 2A to 2D show one embodiment of the method for manufacturing the electrode of the present invention. Figure 2A shows a preparation step for preparing a substrate. Figure 2B shows a metal substrate placement step in which a metal substrate is placed on one side of the substrate in the thickness direction. Figure 2C shows a conductive carbon layer placement step in which a conductive carbon layer is placed on one side of the metal substrate in the thickness direction. Figure 2D shows a protective layer placement step in which a protective layer covering the conductive carbon layer is placed on one side of the conductive carbon layer in the thickness direction. This is an image processing diagram showing the results of Si mapping on one side of the thickness direction of the electrode of Example 1 by Auger electron spectroscopy. This is an image processing diagram showing the results of Si mapping on one side of the thickness direction of the electrode of Example 2 by Auger electron spectroscopy. This is an image processing diagram showing the results of Si mapping on one side of the thickness direction of the electrode of Example 3 by Auger electron spectroscopy. This is an image processing diagram showing the results of Si mapping on one side of the thickness direction of the electrode of Comparative Example 1 by Auger electron spectroscopy. This is an image processing diagram showing the results of Si mapping on one side of the thickness direction of the electrode of Comparative Example 2 by Auger electron spectroscopy.

[0017] An embodiment of the electrode of the present invention will be described with reference to Figure 1.

[0018] In Figure 1, the vertical direction of the paper is the vertical direction (thickness direction). The upper side of the paper is the upper side (one side in the thickness direction). The lower side of the paper is the lower side (the other side in the thickness direction). The horizontal direction and depth direction of the paper are plane directions perpendicular to the vertical direction. Specifically, these correspond to the directional arrows in each figure.

[0019] 1. As shown in Electrode Figure 1, the electrode 1 has a plate shape or film shape (including a sheet shape) with a predetermined thickness. The electrode 1 extends in a plane direction perpendicular to the thickness direction. The electrode 1 has a flat upper surface and a flat lower surface.

[0020] The electrode 1 includes, in order from one side in the thickness direction, a base material 2, a metal underlayer 3, a conductive carbon layer 4, and a protective layer 5. Specifically, the electrode 1 includes a base material 2, a metal underlayer 3 directly disposed on the upper surface (one side in the thickness direction) of the base material 2, a conductive carbon layer 4 directly disposed on the upper surface (one side in the thickness direction) of the metal underlayer 3, and a protective layer 5 covering one surface in the thickness direction of the conductive carbon layer 4. The electrode 1 preferably consists of the base material 2, the metal underlayer 3, the conductive carbon layer 4, and the protective layer 5.

[0021] From the perspective of handling properties, the thickness of the electrode 1 is, for example, 10 μm to 1000 μm, preferably 25 μm to 500 μm, and more preferably 50 μm to 250 μm.

[0022] <Base material> The base material 2 has, for example, a plate shape or a film shape. The base material 2 is the lowermost layer of the electrode 1.

[0023] Examples of the material of the base material 2 include resin, ceramics, and metal. From the perspective of flexibility, the material of the base material 2 preferably includes resin. In other words, the base material 2 is preferably a resin film.

[0024] Examples of the resin include polyester resin, (meth)acrylic resin, olefin resin, polycarbonate resin, polyethersulfone resin, polyarylate resin, melamine resin, polyamide resin, polyimide resin, cellulose resin, and polystyrene resin. Examples of the polyester resin include polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. Examples of the (meth)acrylic resin include polymethyl methacrylate. Examples of the olefin resin include polyethylene, polypropylene, and cycloolefin polymer. Examples of the cellulose resin include triacetyl cellulose.

[0025] The resin preferably includes polyester resin. More preferably, the resin includes polyethylene terephthalate.

[0026] The resin can be used alone or in combination of two or more kinds.

[0027] The thickness of the base material 2 is obtained by subtracting the thickness (nm) of the metal underlayer 3 and the thickness (nm) of the conductive carbon layer 4 from the thickness (μm) of the above-described electrode 1. For example, it is 10 μm to 1000 μm, preferably 25 μm to 500 μm, more preferably 50 μm to 250 μm.

[0028] The thickness of the base material 2 can be measured using a dial gauge (manufactured by PEACOCK, "DG-205").

[0029] <Metal underlayer> The metal underlayer 3 has a film shape. The metal underlayer 3 assists the conductivity of the conductive carbon layer 4.

[0030] The metal underlayer 3 is arranged over the entire upper surface of the base material 2 so as to contact the upper surface of the base material 2. The metal underlayer 3 is arranged between the base material 2 and the conductive carbon layer 4.

[0031] The material of the metal underlayer 3 is a metal. Examples of the metal include titanium, tantalum, chromium, molybdenum, tungsten, and niobium. From the viewpoint of improving the activity with respect to the ferrocyanide compound (described later), niobium is preferably used as the material of the metal underlayer 3. In other words, the metal underlayer 3 is preferably a niobium layer.

[0032] The material of the metal underlayer 3 can be used alone or in combination of two or more kinds.

[0033] Although the metal underlayer 3 will be described in detail later, it is formed by a sputtering method. That is, the metal underlayer 3 is preferably a sputtering layer.

[0034] The thickness of the metal underlayer 3 is, for example, 1 nm to 200 nm, preferably 3 nm to 100 nm, more preferably 5 nm to 80 nm, still more preferably 7 nm to 60 nm, particularly preferably 9 nm to 50 nm, still further preferably 11 nm to 40 nm, and still further preferably 13 nm to 30 nm.

[0035] Specifically, from the perspective of reducing the surface resistance of the electrode 1, the thickness of the metal underlayer 3 is, for example, 1 nm or more, preferably 3 nm or more, more preferably 5 nm or more, still more preferably 7 nm or more, particularly preferably 9 nm or more, further 11 nm or more, and further 13 nm or more. Also, from the perspective of improving adhesion and suppressing crack generation, for example, it is 200 nm or less, preferably 100 nm or less, more preferably 80 nm or less, still more preferably 60 nm or less, particularly preferably 50 nm or less, further 40 nm or less, and further 30 nm or less.

[0036] The thickness of the metal underlayer 3 and the thickness of the conductive carbon layer can be measured by cross-sectional observation using a field emission transmission electron microscope.

[0037] <Conductive Carbon Layer> The conductive carbon layer 4 has a film shape. The conductive carbon layer 4 is disposed over the entire upper surface of the metal underlayer 3 so as to contact the upper surface of the metal underlayer 3.

[0038] The conductive carbon layer 4, for example, has sp ３ bonds and sp ３ bonds. That is, the conductive carbon layer 4 has, for example, a graphite-type structure and a diamond structure. Thereby, the conductive carbon layer 4 can improve conductivity and can improve the activity with respect to a test substance (described later).

[0039] The sp ３ number of bonded atoms and the sp ２ ratio of the number of sp ３ bonded atoms to the sum of the number of sp ３ bonded atoms and the number of sp ３ bonded atoms (sp ２ / sp

[0040] is, for example, 0.1 to 0.9, preferably 0.2 to 0.5. ２ The above ratio can be calculated based on the peak intensity of the sp ３ bond and the peak intensity of the sp

[0041] The conductive carbon layer 4 is formed by a sputtering method, as will be described in more detail later. In other words, the conductive carbon layer 4 is preferably a sputtered layer.

[0042] The thickness of the conductive carbon layer 4 is, for example, 1 nm to 20 nm, preferably 2 nm to 17 nm, more preferably 2.5 nm to 15 nm, even more preferably 3 nm to 13 nm, particularly preferably 3.5 nm to 11 nm, even more preferably 4 nm to 9 nm, and even more preferably 4.5 nm to 7 nm.

[0043] More specifically, the thickness of the conductive carbon layer 4 is, for example, 1 nm or more, preferably 2 nm or more, more preferably 2.5 nm or more, even more preferably 3 nm or more, particularly preferably 3.5 nm or more, even more preferably 4 nm or more, and even more preferably 4.5 nm or more, from the viewpoint of improving the performance of the electrode 1. Furthermore, from the viewpoint of ensuring adhesion with the metal underlayer 3, the thickness is, for example, 20 nm or less, preferably 17 nm or less, more preferably 15 nm or less, even more preferably 13 nm or less, particularly preferably 11 nm or less, even more preferably 9 nm or less, and even more preferably 7 nm or less.

[0044] The thickness of the conductive carbon layer 4 can be measured by cross-sectional observation using a field emission transmission electron microscope.

[0045] <Protective Layer> The protective layer 5 is the uppermost layer of the electrode 1. The protective layer 5 covers one side in the thickness direction of the conductive carbon layer 4 so as to be in contact with the upper surface of the conductive carbon layer 4.

[0046] The protective layer 5 is a hydrophilic protective layer. The fact that the protective layer 5 is hydrophilic means that it is more hydrophilic than the conductive carbon layer 4. High hydrophilicity means, for example, a low water contact angle. By arranging the hydrophilic protective layer 5 on one side of the conductive carbon 4 in the thickness direction, the hydrophilicity of one side of the electrode 1 in the thickness direction is improved. The water contact angle of the protective layer 5 is, for example, 80° or less. From the viewpoint of ensuring hydrophilicity of the electrode 1 surface, it is preferably 60° or less, more preferably 40° or less, even more preferably 20° or less, even more preferably 15° or less, particularly preferably 10° or less, especially preferably 9° or less, and most preferably 7° or less. It is also 0° or more.

[0047] The protective layer 5 either covers the entire surface of one side of the conductive carbon layer 4 in the thickness direction, or partially covers one side of the conductive carbon layer 4 in the thickness direction. From the viewpoint of improving the performance of the electrode 1, it is preferable that the protective layer 5 partially covers one side of the conductive carbon layer 4 in the thickness direction.

[0048] The protective layer 5 covering the entire surface of one side in the thickness direction of the conductive carbon layer 4 is described in more detail as follows: The protective layer 5 is provided in a layered manner on the entire upper surface of the conductive carbon layer 4. Then, one side in the thickness direction of the electrode 1 includes only the protective layer 5, and the conductive carbon layer 4 is not exposed.

[0049] The protective layer 5 partially covers one direction in the thickness direction of the conductive carbon layer 4 in the following manner. Specifically, the protective layer 5 is attached and deposited so as to be scattered across the entire upper surface of the conductive carbon layer 4. The conductive carbon layer 4 is exposed except for the scattered portions of the protective layer 5. In other words, one side of the electrode 1 in the thickness direction includes the conductive carbon layer 4 and the protective layer 5, preferably consisting of the conductive carbon layer 4 and the protective layer 5. Specifically, the conductive carbon layer 4 and the protective layer 5 are scattered across one side of the electrode 1 in the thickness direction. To put it another way, when one side of the electrode 1 in the thickness direction is viewed from the other side in the thickness direction, the conductive carbon layer 4 and the protective layer 5 are mixed together, the conductive carbon layer 4 is distributed across the entire surface of one side of the electrode 1 in the thickness direction, and the protective layer 5 is also distributed across the entire surface of one side of the electrode 1 in the thickness direction.

[0050] The protective layer 5 is made of an inorganic material. Examples of inorganic materials include metalloid elements or metallic elements, and their oxides, nitrides, carbides, oxynitrides, carbonides, carbonides, and carbonate nitrides. Examples of metalloid elements include silicon (Si), boron, germanium, arsenic, antimony, and tellurium. Examples of metallic elements include titanium, aluminum, and zirconium. Among these, oxides of metalloid elements are preferred, and more preferably silicon oxide (SiO₂) ２ ) The electrode 1 uses an inorganic material that is more hydrophilic than the conductive carbon layer 4, i.e., an inorganic material with a low water contact angle.

[0051] The materials for protective layer 5 can be used individually or in combination of two or more types.

[0052] The protective layer 5 is formed by a sputtering method, as will be described in more detail later. In other words, the protective layer 5 is preferably a sputtering layer.

[0053] The thickness of the protective layer 5 is, for example, less than 5 nm, preferably less than 4 nm, more preferably less than 3 nm, even more preferably less than 2 nm, and even more preferably less than 1 nm, from the viewpoint of improving the performance of the electrode 1. Also, from the viewpoint of ensuring hydrophilicity of the electrode 1 surface (one side in the thickness direction), it is preferably 0.1 nm or more, more preferably 0.2 nm or more, and even more preferably 0.3 nm or more.

[0054] If the protective layer 5 covers the entire surface of one side in the thickness direction of the conductive carbon layer 4, the thickness of the protective layer 5 is preferably less than 3 nm, more preferably less than 2 nm, and even more preferably less than 1 nm, from the viewpoint of improving the performance of the electrode 1.

[0055] The thickness of the protective layer 5 can be estimated by cross-sectional observation using a field emission transmission electron microscope, or by measuring the X-ray intensity using X-ray fluorescence analysis (XRF), using a calibration curve prepared in advance using standard samples.

[0056] The water contact angle on one side of the electrode 1 in the thickness direction is preferably 80° or less. From the viewpoint of ensuring hydrophilicity of the electrode 1 surface, it is preferably 60° or less, more preferably 40° or less, even more preferably 20° or less, even more preferably 15° or less, particularly preferably 10° or less, especially preferably 9° or less, and most preferably 7° or less. It is also 0° or more.

[0057] The water contact angle can be measured using a water contact angle measuring device (product name "Dmo-501", manufactured by Kyowa Interface Chemical Co., Ltd.) by the droplet method under an atmosphere of 23°C and 30% RH humidity. Specifically, 2 μL of distilled water is dropped, and the water contact angle is measured from the droplet shape 1000 milliseconds after dropping.

[0058] On one side of the electrode 1 in the thickness direction, the proportion of elements derived from the inorganic material of the protective layer 5 is 30 atomic percent or less, as measured by Auger electron spectroscopy. From the viewpoint of improving the performance of the electrode 1, it is preferably 25 atomic percent or less, more preferably 20 atomic percent or less, even more preferably 15 atomic percent or less, even more preferably 10 atomic percent or less, and particularly preferably 5 atomic percent or less. Also, from the viewpoint of ensuring hydrophilicity of the electrode 1 surface, it is preferably 1 atomic percent or more, more preferably 2 atomic percent or more, and even more preferably 3 atomic percent or more.

[0059] On one side of the electrode 1 in the thickness direction, the proportion of carbon derived from the conductive carbon layer 4, as measured by Auger electron spectroscopy, is, for example, 25 atomic% or more and 95 atomic% or less. From the viewpoint of improving the performance of the electrode 1, it is preferably 40 atomic% or more, more preferably 50 atomic% or more, even more preferably 60 atomic% or more, even more preferably 70 atomic% or more, and particularly preferably 80 atomic% or more. Also, from the viewpoint of ensuring hydrophilicity of the electrode 1 surface, it is preferably 90 atomic% or less, more preferably 88 atomic% or less, and even more preferably 85 atomic% or less.

[0060] On one side of the electrode 1 in the thickness direction, the atomic composition measured by Auger electron spectroscopy shows that the ratio of elements derived from the inorganic material of the protective layer 5 to the ratio of carbon derived from the conductive carbon layer 4 (ratio of elements derived from inorganic material / ratio of carbon) is, for example, 0.01 or more and 1.2 or less. From the viewpoint of improving the performance of the electrode 1, it is preferably 0.8 or less, more preferably 0.5 or less, even more preferably 0.2 or less, even more preferably 0.1 or less, and particularly preferably 0.06 or less. From the viewpoint of ensuring hydrophilicity of the electrode 1 surface, it is preferably 0.02 or more.

[0061] The atomic composition can be measured by Auger electron spectroscopy on one side in the thickness direction of the manufactured electrode 1 using an Auger electron spectrometer (Model 680, ULVAC-PHI). Specifically, the measurement is performed under electron gun conditions of an acceleration voltage of 10 kV, a sample current of 10 nA, and an angle of 30° with respect to the sample normal, while the sample is neutralized by an argon ion gun.

[0062] Auger electron spectroscopy can measure the atomic composition of atoms contained within a range of approximately 5 nm in depth from one side in the thickness direction of electrode 1.

[0063] 2. Method of manufacturing the electrode The method of manufacturing the electrode 1 will be explained with reference to Figures 2A to 2D.

[0064] The method for manufacturing the electrode 1 comprises a preparation step of preparing a base material 2, a metal base layer placement step of placing a metal base layer 3 on one side of the base material 2 in the thickness direction, a conductive carbon layer placement step of placing a conductive carbon layer 4 on one side of the metal base layer 3 in the thickness direction, and a protective layer placement step of placing a protective layer 5 covering the conductive carbon layer 4 on one side of the conductive carbon layer 4 in the thickness direction. Furthermore, this method is preferably carried out using a roll-to-roll method. In such cases, the transport speed is, for example, 0.1 m / min to 20.0 m / min, preferably 0.5 m / min to 10.0 m / min, and more preferably 1.0 m / min to 3.0 m / min.

[0065] [Preparation Step] In the preparation step, the base material 2 is prepared as shown in Figure 2A.

[0066] [Metal Substrate Placement Process] In the metal substrate placement process, as shown in Figure 2B, the metal substrate 3 is placed on one side of the substrate 2 in the thickness direction.

[0067] Examples of methods for forming the metal underlayment 3 include a dry method and a wet method. Preferably, the dry method is used for forming the metal underlayment 3.

[0068] Examples of dry methods include PVD (Physical Vapor Deposition) and CVD (Chemical Vapor Deposition). Preferably, the PVD method is preferred. Examples of PVD methods include sputtering, vacuum deposition, laser deposition, and ion plating. Preferably, the sputtering method is preferred for PVD. More preferably, magnetron sputtering (magnetron DC discharge or magnetron DC pulsed discharge) is used.

[0069] In the sputtering method, a target (material for the metal underlayment 3) and a substrate 2 are placed facing each other in a vacuum chamber. Then, by supplying sputtering gas and applying voltage from a power source, gas ions are accelerated and irradiated onto the target, ejecting the target material from the target surface. This target material is then deposited on the surface (one side in the thickness direction) of the substrate 2 to form the metal underlayment 3.

[0070] Examples of sputtering gases include inert gases (such as argon gas).

[0071] The film deposition pressure is, for example, 0.05 Pa to 1.00 Pa, preferably 0.10 Pa to 0.50 Pa, and more preferably 0.15 Pa to 0.30 Pa.

[0072] The power supply may be, for example, a DC power supply, an AC power supply, an MF power supply, or an RF power supply. A combination of these may also be used.

[0073] The discharge power is, for example, 1.0 W / cm². ２ ~40.0 W / cm ２ Preferably, 2.0 W / cm² ２ ~20.0 W / cm ２ , comfortably, 2.5 W / cm ２ ~10.0 W / cm ２ More preferably, 3.0 W / cm² ２ ~5.0 W / cm ２ That is the case.

[0074] The temperature of the substrate 2 (film formation temperature) is, for example, -10°C to 200°C, preferably 20°C to 100°C, and more preferably 30°C to 60°C.

[0075] This places the metal underlayer 3 on one side of the base material 2 in the thickness direction.

[0076] [Conductive Carbon Layer Placement Process] In the conductive carbon layer placement process, as shown in Figure 2C, the conductive carbon layer 4 is placed on one side in the thickness direction of the metal substrate layer 3. In other words, in the conductive carbon layer placement process, the conductive carbon layer 4 is placed on one side in the thickness direction of the substrate 2.

[0077] The method for forming the conductive carbon layer 4 is the same as the method for forming the metal underlayer 3 described above. A preferred method for forming the conductive carbon layer 4 is sputtering. More preferably, magnetron sputtering (magnetron DC discharge or magnetron DC pulsed discharge) is used.

[0078] In the sputtering method, sintered carbon is selected as the target.

[0079] Examples of sputtering gases include inert gases (such as argon gas).

[0080] Furthermore, in the conductive carbon layer placement process, a reactive gas (e.g., oxygen gas) can be introduced along with the sputtering gas.

[0081] The film deposition pressure is, for example, 0.05 Pa to 1.00 Pa, preferably 0.10 Pa to 0.50 Pa, and more preferably 0.15 Pa to 0.30 Pa.

[0082] The power supply may be, for example, a DC power supply, an AC power supply, an MF power supply, or an RF power supply. A combination of these may also be used.

[0083] The discharge power is, for example, 0.5 W / cm². ２ ~30.0 W / cm ２ Preferably, 1.0 W / cm² ２ ~20.0 W / cm ２ More preferably, 5.0 W / cm² ２ ~10.0 W / cm ２ That is the case.

[0084] The temperature of the substrate 2 (film formation temperature) is, for example, -10°C to 200°C, preferably 20°C to 100°C, and more preferably 30°C to 60°C.

[0085] This allows the conductive carbon layer 4 to be placed on one side in the thickness direction of the metal underlayer 3.

[0086] [Protective layer placement process] In the protective layer placement process, as shown in Figure 2D, a protective layer 5 that covers the conductive carbon layer 4 is placed on one side in the thickness direction of the conductive carbon layer 4 to manufacture the electrode 1.

[0087] In the protective layer placement step, the protective layer 5 is placed to cover the entire surface of one side in the thickness direction of the conductive carbon layer 4, or to partially cover one side in the thickness direction of the conductive carbon layer 4. From the viewpoint of improving the performance of the electrode 1, it is preferable that the protective layer 5 partially covers one side in the thickness direction of the conductive carbon layer 4.

[0088] Examples of methods for forming the protective layer 5 include a dry method and a wet method. Preferably, the dry method is used for forming the protective layer 5.

[0089] Examples of dry methods include PVD (Physical Vapor Deposition) and CVD (Chemical Vapor Deposition). Preferably, the PVD method is preferred. Examples of PVD methods include sputtering, vacuum deposition, laser deposition, and ion plating. Preferably, the sputtering method is preferred for PVD. More preferably, magnetron sputtering (magnetron DC discharge or magnetron DC pulsed discharge) is used.

[0090] In the sputtering method, one of the above-mentioned inorganic materials (preferably silicon) is selected as the target.

[0091] Reactive gases are used as sputtering gases. Examples of reactive gases include oxygen, nitrogen, ammonia, and water vapor (H). ２ O) is one example. Preferably, it is oxygen.

[0092] Reactive gases can be used individually or in combination of two or more types.

[0093] In addition to the reactive gas, an inert gas (for example, argon gas) can be used. The content of the inert gas is, for example, 0% by mass or more and 10% by mass or less. From the viewpoint of reducing the thickness of the protective layer, it is preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 1% by mass or less, and particularly preferably 0% by mass. The inert gas increases the formation rate of the protective layer 5 and increases its thickness. Therefore, it is preferable not to use an inert gas in the protective layer placement process.

[0094] In the protective layer placement process, a reactive gas is used as the sputtering gas, resulting in a significantly slower film deposition rate compared to the metal substrate placement process and the conductive carbon layer placement process, which use argon gas as the sputtering gas. Specifically, the film deposition rate in the protective layer placement process is about 1 / 100 to 1 / 2 of the film deposition rate in the metal substrate placement process and the conductive carbon layer placement process. Therefore, even when film deposition is performed continuously at a similar transport speed using a roll-to-roll method, for example, an electrode can be obtained in which the conductive carbon layer 4 is covered by a protective layer 5 that is thinner than the metal substrate 3 and the conductive carbon layer 4, preferably partially covered by the protective layer 5, and has a conductive carbon layer 4 on one side in the thickness direction.

[0095] In the protective layer placement process, the thickness of the protective layer can be controlled by appropriately controlling the transport speed in the apparatus. From the viewpoint of appropriately placing the protective layer 5 and ensuring the hydrophilicity of the electrode 1, the transport speed is, for example, 0.1 m / min or more, preferably 0.4 m / min or more, and more preferably 0.8 m / min or more. From the viewpoint of preventing the protective layer 5 from becoming too thick and degrading the performance of the electrode 1, the transport speed is 20.0 m / min or less, preferably 10.0 m / min or less, and more preferably 2.0 m / min or less.

[0096] The film deposition pressure is, for example, 0.05 Pa or more, preferably 0.10 Pa or more, more preferably 0.15 Pa or more, and even more preferably 0.20 Pa or more. Alternatively, it may be 3.00 Pa or less, preferably 2.50 Pa or less, more preferably 2.00 Pa or less, and even more preferably 0.50 Pa or less.

[0097] The power supply may be, for example, a DC power supply, an AC power supply, an MF power supply, or an RF power supply. A combination of these may also be used.

[0098] The discharge power is, for example, 0.10 W / cm². ２ Preferably, 0.20 W / cm² ２ More preferably, 0.30 W / cm² ２ That's all. Also, for example, 20.0 W / cm² ２ Preferably, 15.0 W / cm² ２More preferably, 10.0 W / cm² ２ More preferably, 5.0 W / cm² ２ The following applies:

[0099] The temperature of the substrate 2 (film formation temperature) is, for example, -10°C to 200°C, preferably 20°C to 100°C, and more preferably 30°C to 60°C.

[0100] This allows for the manufacture of the electrode 1 by placing a protective layer 5 covering the conductive carbon layer 4 on one side in the thickness direction of the conductive carbon layer 4.

[0101] Electrode 1 has a conductive carbon layer 4 and a protective layer 5 on one side in the thickness direction. Furthermore, in the aforementioned one side in the thickness direction of electrode 1, the proportion of elements derived from the inorganic material of the protective layer 5 is 30 atomic percent or less, as measured by Auger electron spectroscopy. Therefore, hydrophilicity can be maintained for a long period of time while maintaining high performance as electrode 1.

[0102] Therefore, electrode 1 can be suitably used, in particular, as an electrode in a biosensor. In other words, electrode 1 is preferably a biosensor electrode.

[0103] 3. Biosensors In the following explanation, a blood glucose sensor will be used as an example of a biosensor and described in detail. In a blood glucose sensor, the test substance is, for example, a ferrocyanine compound. The following explanation will describe in detail the case where the test substance is a ferrocyanine compound.

[0104] The blood glucose sensor is equipped with an electrode 1 and a reagent layer arranged sequentially in one direction in the thickness direction.

[0105] The reagent layer contains an enzyme and a ferricyanine compound or a ferrocyanine compound.

[0106] An example of an enzyme is glucose oxidase.

[0107] Examples of ferricyanide compounds include potassium ferricyanide and sodium ferricyanide. Potassium ferricyanide is preferred as the ferricyanide compound.

[0108] Examples of ferrocyanide compounds include potassium ferrocyanide and sodium ferrocyanide.

[0109] The following describes in detail a method for detecting glucose in the blood using a blood glucose sensor, specifically focusing on the case where the reagent layer contains an enzyme and potassium ferricyanide.

[0110] In this method, blood is first added to one side of the reagent layer in the thickness direction. At this time, the glucose in the blood is oxidized by the enzyme in the reagent layer. The enzyme then reduces potassium ferricyanide to potassium ferrocyanide.

[0111] Next, a voltage is applied to the blood glucose sensor. This causes potassium ferrocyanide to oxidize to potassium ferricyanide.

[0112] By measuring the current flowing during the above oxidation reaction, glucose in the blood can be indirectly detected.

[0113] The blood glucose sensor is equipped with electrode 1. Therefore, it maintains high performance while excelling at retaining hydrophilicity over a long period of time.

[0114] 4. The electrode 1 has a protective layer 5 on one side in the thickness direction. Furthermore, on the aforementioned side in the thickness direction of the electrode 1, the proportion of elements derived from the inorganic material of the protective layer 5 is 30 atomic percent or less, as measured by Auger electron spectroscopy. Therefore, hydrophilicity can be maintained for a long period of time while maintaining high performance as an electrode 1.

[0115] More specifically, in electrode 1, one surface in the thickness direction of electrode 1 includes a hydrophilic protective layer 5 made of an inorganic material with higher hydrophilicity than the conductive carbon layer 4. Therefore, the hydrophilicity of the electrode 1 surface (one surface in the thickness direction) that comes into contact with the measurement sample can be improved.

[0116] Furthermore, in electrode 1, in one direction in the thickness direction, measurement of the atomic composition by Auger electron spectroscopy shows that the proportion of elements derived from the inorganic material of the protective layer 5 is 30 atomic percent or less. In other words, the conductive carbon layer 4 is covered by the protective layer 5. Therefore, electrode 1 can improve its hydrophilicity while maintaining its high performance as an electrode 1.

[0117] Furthermore, compared to the case where hydrophilicity is imparted to the conductive carbon layer 4 by a general surface treatment, when a hydrophilic protective layer 5 made of inorganic material is applied, the hydrophilicity is maintained for a long period of time, for example, several months or several years. This is because the hydrophilicity of the inorganic material forming the protective layer itself does not usually deteriorate significantly and is maintained. As a result, the electrode 1 can maintain a state where reagents can be easily applied to the electrode surface for a long period of time, and the lifespan of the electrode can be extended. Consequently, when the electrode 1 is used in a biosensor, the lifespan of the biosensor can be extended.

[0118] 5. Modified Examples In the modified examples, the same reference numerals are used for components and processes as in the first embodiment, and their detailed descriptions are omitted. Furthermore, the modified examples can achieve the same effects and advantages as the first embodiment unless otherwise specified. Moreover, the first embodiment and the modified examples can be combined as appropriate.

[0119] In the above description, the electrode 1 comprises a base material 2, a metal underlayer 3, a conductive carbon layer 4, and a protective layer 5 in order toward one side in the thickness direction. However, the electrode 1 does not necessarily have a metal underlayer 3. In such cases, the electrode 1 comprises a base material 2, a conductive carbon layer 4, and a protective layer 5 in order toward one side in the thickness direction. Preferably, the electrode 1 includes a metal underlayer 3 from the viewpoint of improving activity toward ferrocyanine compounds.

[0120] The electrode 1 may also include other layers (e.g., a hard coat layer, a gas barrier layer) besides the substrate 2, the metal underlayer 3, the conductive carbon layer 4, and the protective layer 5. More specifically, the electrode 1 may include other layers on other surfaces in the thickness direction of the substrate 2, between the substrate 2 and the metal underlayer 3, between the metal underlayer 3 and the conductive carbon layer 4, and on one surface in the thickness direction of the conductive carbon layer 4.

[0121] The hard coat layer is a scratch-protective layer that makes it difficult for scratches to occur on the electrode 1. Specifically, the electrode 1 preferably has a hard coat layer on one surface in the thickness direction and / or the other surface in the thickness direction of the substrate 2.

[0122] Furthermore, if the electrode 1 includes other layers, the thickness of the substrate 2 is obtained by subtracting the thickness of the metal underlayer 3 (nm), the thickness of the conductive carbon layer 4 (nm), the thickness of the protective layer 5 (nm), and the thickness of the other layers (nm) from the thickness of the electrode 1 (μm).

[0123] In the above explanation, electrode 1 was described as an electrode for a biosensor, but it is not limited to this. It can also be used as an electrode for electrochemical measurements targeting ferrocyanine compounds, specifically as a working electrode for cyclic voltammetry (CV).

[0124] The present invention will be further described below with reference to examples and comparative examples. However, the present invention is not limited in any way to the examples and comparative examples. Furthermore, specific numerical values ​​such as blending ratios (content ratios), physical properties, and parameters used in the following description may be replaced with the corresponding upper limits (numerical values ​​defined as "less than or equal to" or "less than") or lower limits (numerical values ​​defined as "greater than or equal to" or") of the blending ratios (content ratios), physical properties, and parameters described in the "Modes for Carrying Out the Invention" above.

[0125] <Electrode Manufacturing> Example 1 The electrode of Example 1 was manufactured according to the following procedure. Details of the manufacturing conditions for Example 1 are shown in Table 1. [Preparation Steps] A film made of polyethylene terephthalate (PET film, thickness: 188 μm) was prepared as the base material. The following steps were carried out using a roll-to-roll method. The conveying speed was 1.5 m / min.

[0126] [Metal Substrate Placement Process] A niobium layer (20 nm thick) was placed on one side of the substrate in the thickness direction using magnetron sputtering. The conditions for magnetron sputtering were as follows: {Conditions} Target type: Niobium (Nb) Discharge power: 3.6 W / cm２ Sputtering gas: Argon gas Deposition pressure: 0.2 Pa Deposition temperature: 40°C Conveying speed: 1.5 m / min

[0127] [Conductive Carbon Layer Placement Process] A conductive carbon layer (thickness: 5 nm) was placed on one side of the niobium layer in the thickness direction using magnetron sputtering. The conditions for magnetron sputtering were as follows: {Conditions} Target type: Sintered carbon (C) Discharge power: 7.8 W / cm ２ Sputtering gas: Argon gas Deposition pressure: 0.2 Pa Deposition temperature: 40°C Conveying speed: 1.5 m / min

[0128] [Protective layer placement process] In the presence of oxygen gas, silicon oxide (SiO₂) is sputtered onto one side of the conductive carbon layer in the thickness direction using magnetron sputtering. ２ A layer was placed. The conditions for magnetron sputtering were as follows. This produced the electrode of Example 1. {Conditions} Target type: Silicon (Si) Discharge power: 0.56 W / cm ２ Oxygen concentration: 98% by volume Sputtering gas: Oxygen gas Deposition pressure: 0.25 Pa Deposition temperature: 40°C Conveying speed: 1.0 m / min

[0129] Example 2 An electrode was manufactured according to the same procedure as in Example 1. However, in the protective layer placement step, the discharge power was set to 7.8 W / cm². ２ The film deposition pressure was changed to 1.59 Pa. Table 1 shows the details of the manufacturing conditions for Example 2.

[0130] Example 3 An electrode was manufactured according to the same procedure as in Example 1. However, in the protective layer placement step, the discharge power was set to 2.6 W / cm². ２ This was changed. The details of the manufacturing conditions for Example 3 are shown in Table 1.

[0131] Comparative Example 1 An electrode was manufactured according to the same procedure as in Example 1. However, in the protective layer placement step, the discharge power was set to 1.1 W / cm². ２ Next, the oxygen gas pressure was changed to 1.56 Pa. Table 1 shows the details of the manufacturing conditions for Comparative Example 1.

[0132] Comparative Example 2: Electrodes were manufactured using the same procedure as in Example 1. However, the protective layer placement step was replaced with the following plasma treatment step. Table 1 shows the details of the manufacturing conditions for Comparative Example 2.

[0133] [Plasma Treatment Process] Plasma treatment was performed on one side in the thickness direction of the conductive carbon layer using a magnetron DC discharge in the presence of oxygen gas, based on the following conditions: {Conditions} Plasma generation method: Magnetron DC discharge Discharge power: 2.6 W / cm ２ Plasma irradiation time: 24 seconds; Oxygen concentration: 98% by volume; Gas: Oxygen; Gas pressure: 0.5 Pa

[0134]

[0135] <Evaluation> [Measurement of Thickness] Using each example and the electrode film and electrode substrate of each example, cross-sectional samples for TEM were prepared by the FIB microsampling method, and the thickness of the metal underlayer, the conductive carbon layer, and the protective layer was measured by cross-sectional observation using a field emission transmission electron microscope (FE-TEM, JOEL Corporation, "JEM-2800"). The results are shown in Tables 1 and 2.

[0136] [Auger Electron Spectroscopy] The atomic composition of one side of the manufactured electrode in the thickness direction was analyzed by measuring it using an Auger electron spectrometer (Model 680, ULVAC-PHI). The measurement was performed under electron gun conditions of an acceleration voltage of 10 kV, a sample current of 10 nA, and an angle of 30° with respect to the sample normal, with the charge neutralized by an argon ion gun. In Auger electron spectroscopy, the atomic composition contained in the electrode from one side in the thickness direction to a depth of approximately 5 nm is analyzed. The atomic compositions of each example and comparative example obtained are shown in Table 2, and the results of Si mapping of one side of the electrode in the thickness direction by Auger electron spectroscopy are shown in Figures 3 to 7. In the figures, the white areas correspond to the locations where Si is present. Example 1 corresponds to Figure 3, Example 2 to Figure 4, Example 3 to Figure 5, Comparative Example 1 to Figure 6, and Comparative Example 2 to Figure 7.

[0137] [Measurement of Water Contact Angle] The water contact angle of one side of the electrode in the thickness direction was measured for each example and comparative example electrode, both initially (specifically, within 12 hours of manufacture) and one week later. The measurement results are shown in Table 2.

[0138] For details, the water contact angle was measured using a water contact angle measuring device (product name "Dmo-501", manufactured by Kyowa Interface Chemical Co., Ltd.) by the droplet method, under conditions of 23°C and 30% RH humidity. First, approximately 2.0 μL of water droplet was dropped onto the center of one side in the electrode thickness direction. Then, one second after dropping, the angle between the substrate surface (one side in the electrode thickness direction) and the tangent to the edge of the dropped water droplet was measured and defined as the "water contact angle (°)". A smaller "water contact angle (°)" indicates superior hydrophilicity.

[0139] In Table 2, "Change" indicates the change in water contact angle from the initial stage to one week later. A smaller "Change" indicates better long-term retention of hydrophilicity. In Comparative Example 1, although hydrophilicity is improved by the arrangement of the protective layer, Auger electron spectroscopy results show that the Si content is too high, resulting in reduced initial electrode activity (large ΔEp) and making it difficult to use as an electrode. Therefore, data on the water contact angle after one week was not obtained.

[0140] [Long-term storage stability of activity against ferrocyanide compounds] The activity (electrode activity) against potassium ferrocyanide was evaluated by cyclic voltammetry (CV) for the electrodes of each example and comparative example, both initially (specifically, within 12 hours of manufacture) and after one week. The measurement results are shown in Table 2.

[0141] In detail, a sample electrode with a known electrode area was prepared by attaching insulating tape with a 2 mm diameter hole to one side of a conductive carbon layer. Cyclic voltammetry (CV) was performed using this sample electrode as the working electrode. Specifically, a 1 M KCl aqueous solution was used as the electrolyte, and 1 mM KCl was used as the electrode active substance. ４ [Fe(CN)] ６ ] ４－The sample electrode was immersed in an aqueous solution containing potassium ferrocyanide. A silver-silver chloride electrode was used as the reference electrode, and a platinum wire as the counter electrode. In the CV measurement, the potential sweep was started from 0V and swept from negative to positive in the range of -0.1V to 0.5V (specifically, the potential was changed in the order of -0.1V, 0.5V, and -0.1V). The potential sweep rate was 0.1V / s. The CV measurement was performed at 23°C. Three CV measurements were performed. The average value of the three ΔEp values ​​in the CV measurement was obtained as ΔEp. A smaller ΔEp indicates a faster electron transfer rate and superior activity towards potassium ferrocyanide.

[0142] In Table 2, the "absolute value of the rate of change" indicates the absolute value of the rate of change in activity toward the ferrocyanine compound from the initial stage to one week later. A smaller "absolute value of the rate of change" indicates better long-term storage of activity toward the ferrocyanine compound. In Comparative Example 1, although the hydrophilicity is improved by the arrangement of the protective layer, Auger electron spectroscopy results show that the Si content is too high, resulting in reduced initial electrode activity (large ΔEp) and making it difficult to use as an electrode. Therefore, data on electrode activity after one week were not obtained.

[0143]

[0144] The above invention is provided as an illustrative embodiment of the present invention, but this is merely illustrative and should not be interpreted restrictively. Modifications of the present invention that are obvious to those skilled in the art are included in the claims below.

[0145] The electrode, biosensor, and method for manufacturing the electrode according to the present invention can be suitably used, for example, in the manufacture of blood glucose sensors.

[0146] 1. Electrode 2. Substrate 3. Metal underlayer 4. Conductive carbon layer 5. Protective layer

Claims

1. An electrode comprising a substrate, a conductive carbon layer disposed on one side of the substrate in the thickness direction, and a hydrophilic protective layer covering one surface of the conductive carbon layer in the thickness direction, wherein the protective layer is made of an inorganic material, one surface of the electrode in the thickness direction includes the protective layer, and the proportion of elements derived from the inorganic material is 30 atomic percent or less, as measured by Auger electron spectroscopy on the one surface of the electrode in the thickness direction.

2. The electrode according to claim 1, wherein the water contact angle of one side in the thickness direction of the electrode is 80° or less.

3. The electrode according to claim 1, wherein the protective layer partially covers one surface of the conductive carbon layer in the thickness direction, and one surface of the electrode in the thickness direction includes the conductive carbon layer and the protective layer.

4. The electrode according to claim 1, wherein the element derived from the inorganic material includes silicon.

5. A biosensor comprising the electrode described in any one of claims 1 to 4.

6. A method for manufacturing an electrode according to any one of claims 1 to 4, comprising: a preparation step of preparing the substrate; a conductive carbon layer placement step of arranging the conductive carbon layer on one side of the substrate in the thickness direction; and a protective layer placement step of arranging the protective layer that covers the conductive carbon layer on one side of the conductive carbon layer in the thickness direction.

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