Electrode, biosensor, and electrode manufacturing method

Abstract

This electrode (1) comprises a substrate film (2) and a conductive carbon layer (4) in this order toward one side in the thickness direction. The electrode (1) satisfies expression (1).　Expression (1): 0.30<N / O<4.00 (In expression (1), N represents the content of nitrogen atoms in the conductive carbon layer, as measured by X-ray photoelectron spectroscopy at a photoelectron extraction angle of 90º with respect to one surface of the conductive carbon layer in the thickness direction, and O represents the content of oxygen atoms in the conductive carbon layer, as measured by X-ray photoelectron spectroscopy at a photoelectron extraction angle of 90º with respect to one surface of the conductive carbon layer in the thickness direction.)

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.

[0003] As such an electrode, for example, an electrode comprising a substrate and a conductive carbon layer has been proposed (see, for example, Patent Document 1 below).

[0004] Japanese Patent Publication No. 2021-56205

[0005] Depending on the application, such biosensors may require a longer shelf life.

[0006] The present invention provides an electrode with excellent long-term storage properties and activity for a test substance, a biosensor equipped with the electrode, and a method for manufacturing the electrode.

[0007] The present invention [1] includes an electrode comprising a base film and a conductive carbon layer arranged sequentially toward one side in the thickness direction, satisfying the following formula (1): 0.30 < N / O < 4.00 (1) (In the above formula (1), N represents the nitrogen atom content in the conductive carbon layer measured by X-ray photoelectron spectroscopy with a photoelectron extraction angle of 90° with respect to one side in the thickness direction of the conductive carbon layer, and O represents the oxygen atom content in the conductive carbon layer measured by X-ray photoelectron spectroscopy with a photoelectron extraction angle of 90° with respect to one side in the thickness direction of the conductive carbon layer.)

[0008] The present invention [2] further includes the electrode described in [1] above, which satisfies the following formula (2): 0.100 < O / C (2) (In formula (2) above, O represents the oxygen atom content in the conductive carbon layer measured by X-ray photoelectron spectroscopy with a photoelectron extraction angle of 90° with respect to one side in the thickness direction of the conductive carbon layer, and C represents the carbon atom content in the conductive carbon layer measured by X-ray photoelectron spectroscopy with a photoelectron extraction angle of 90° with respect to one side in the thickness direction of the conductive carbon layer.)

[0009] The present invention [3] is that the conductive carbon layer is, for example, sp ２ Joining and / or sp ３ It includes the electrode described in [1] or [2] above, which has a bond.

[0010] The present invention [4] includes a biosensor comprising the electrode described in any one of the above [1] to [3].

[0011] The present invention [5] is a method for manufacturing an electrode according to any one of the above [1] to [3], comprising a preparation step of preparing a base film, a conductive carbon layer arrangement step of arranging a conductive carbon layer on one side of the base film in the thickness direction to manufacture a laminate, and a plasma treatment step of performing plasma treatment on one side of the laminate in the thickness direction in the presence of oxygen gas and nitrogen gas.

[0012] The electrode of the present invention satisfies the following formula (1). Therefore, it has excellent long-term storage properties and activity with respect to the test substance. 0.30 < N / O < 4.00 (1) (In the above formula (1), N represents the nitrogen atom content in the conductive carbon layer measured by X-ray photoelectron spectroscopy with a photoelectron extraction angle of 90° to one side in the thickness direction of the conductive carbon layer, and O represents the oxygen atom content in the conductive carbon layer measured by X-ray photoelectron spectroscopy with a photoelectron extraction angle of 90° to one side in the thickness direction of the conductive carbon layer.)

[0013] The biosensor of the present invention is equipped with the electrode of the present invention. Therefore, it has excellent long-term storage properties and activity for the test substance.

[0014] The method for manufacturing an electrode of the present invention includes a plasma treatment step of performing plasma treatment on one surface in the thickness direction of a conductive carbon layer in the presence of oxygen gas and nitrogen gas. Therefore, an electrode satisfying the above formula (1) can be manufactured.

[0015] FIG. 1 is a schematic cross-sectional view of an embodiment of the electrode of the present invention. FIGS. 2A to 2D show an embodiment of the method for manufacturing the electrode of the present invention. FIG. 2A shows a preparation step of preparing a base film. FIG. 2B shows a metal underlayer arrangement step of arranging a metal underlayer on one surface in the thickness direction of the base film. FIG. 2C shows a conductive carbon layer arrangement step of arranging a conductive carbon layer on one surface in the thickness direction of the metal underlayer to manufacture a laminate. FIG. 2D shows a plasma treatment step of performing plasma treatment on one surface in the thickness direction of the laminate in the presence of oxygen gas and nitrogen gas. FIGS. 3A to 3C show explanatory views of functional groups in the conductive carbon layer. FIG. 3A is an explanatory view of a functional group containing oxygen. FIG. 3B shows an explanatory view of a functional group containing nitrogen. FIG. 3C shows an explanatory view of a functional group containing oxygen and nitrogen.

[0016] Referring to FIG. 1, an embodiment of the electrode of the present invention will be described.

[0017] In FIG. 1, the vertical direction on the paper surface is the vertical direction (thickness direction). Also, the upper side on the paper surface is the upper side (one side in the thickness direction). Also, the lower side on the paper surface is the lower side (the other side in the thickness direction). Also, the left-right direction and the depth direction on the paper surface are plane directions orthogonal to the vertical direction. Specifically, it conforms to the direction arrows in each figure.

[0018] <Electrode> As shown in FIG. 1, the electrode 1 has a film shape (including a sheet shape) having a predetermined thickness. The electrode 1 extends in a plane direction orthogonal to the thickness direction. The electrode 1 has a flat upper surface and a flat lower surface.

[0019] The electrode 1 includes a base material film 2, a metal underlayer 3, and a conductive carbon layer 4 in this order toward one side in the thickness direction. Specifically, the electrode 1 includes a base material film 2, a metal underlayer 3 directly disposed on the upper surface (one surface in the thickness direction) of the base material film 2, and a conductive carbon layer 4 directly disposed on the upper surface (one surface in the thickness direction) of the metal underlayer 3. The electrode 1 preferably consists of a base material film 2, a metal underlayer 3, and a conductive carbon layer 4.

[0020] From the viewpoint of handling property, 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.

[0021] <Base material film> The base material film 2 has a film shape. The base material film 2 is the lowermost layer of the electrode 1.

[0022] Examples of the material of the base material film 2 include resin, ceramics, and metal. From the viewpoint of flexibility, the material of the base material film 2 preferably includes resin. In other words, the base material film 2 is preferably a resin film.

[0023] 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.

[0024] The resin preferably includes polyester resin. More preferably, the resin includes polyethylene terephthalate.

[0025] The resin can be used alone or in combination of two or more kinds.

[0026] The thickness of the base film 2 is obtained by subtracting the thickness of the metal underlayer 3 (nm) and the thickness of the conductive carbon layer 4 (nm) from the thickness of the electrode 1 (μm) described above, and is, for example, 10 μm to 1000 μm, preferably 25 μm to 500 μm, and more preferably 50 μm to 250 μm.

[0027] The thickness of the base film 2 can be measured using a dial gauge (PEACOCK, "DG-205").

[0028] <Metal underlayment> The metal underlayment 3 assists in the conductivity of the conductive carbon layer 4.

[0029] The metal underlayer 3 is positioned over the entire upper surface of the base film 2 so as to be in contact with the upper surface of the base film 2. The metal underlayer 3 is positioned between the base film 2 and the conductive carbon layer 4.

[0030] The material of the metal underlayer 3 is a metal. Examples of metals include titanium, tantalum, chromium, molybdenum, tungsten, and niobium. Preferably, the material of the metal underlayer 3 is niobium, from the viewpoint of improving the activity of the substance to be tested (described later). In other words, the metal underlayer 3 is preferably a niobium layer.

[0031] The materials for the metal underlayment 3 can be used individually or in combination of two or more types.

[0032] The metal underlayer 3 is formed by a sputtering method, as will be described in more detail later. In other words, the metal underlayer 3 is preferably a sputtering layer.

[0033] 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, even more preferably 7 nm to 60 nm, particularly preferably 9 nm to 50 nm, even more preferably 11 nm to 40 nm, and even more preferably 13 nm to 30 nm.

[0034] 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 preferably 11 nm or more, and further preferably 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 preferably 40 nm or less, and further preferably 30 nm or less.

[0035] <Conductive Carbon Layer> The conductive carbon layer 4 has a film shape. The conductive carbon layer 4 is disposed on the entire upper surface of the metal underlayer 3 so as to contact the upper surface of the metal underlayer 3. The conductive carbon layer 4 is the uppermost layer of the electrode 1.

[0036] The conductive carbon layer 4 has, for example, sp ２ bonds and / or 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 the activity with respect to a test substance (described later).

[0037] The number of atoms bonded by sp ３ and the ratio of the number of atoms bonded by sp ２ to the sum of the number of atoms bonded by sp ３ (sp ３ / sp ３ + sp ２ ) is, for example, 0.1 to 0.9, preferably 0.2 to 0.5.

[0038] Also, the sp ２ ratio is 25% to 55%, preferably 35% to 50%, with respect to the sum of the number of atoms bonded by sp ３ and the number of atoms bonded by sp ２ .

[0039] Also, the sp ３ ratio is ３ with respect to the sum of the number of atoms bonded by sp ２The sum of the number of bonded atoms is 12% to 35%, preferably 20% to 27%.

[0040] The above ratio is obtained in the spectrum obtained by measuring one side in the thickness direction of the conductive carbon layer 4 by X-ray photoelectron spectroscopy, where sp ２ Binding peak intensity and sp ３ It can be calculated based on the peak intensity of the binding.

[0041] The conductive carbon layer 4 contains an oxygen-containing functional group, a nitrogen-containing functional group, and a functional group containing both oxygen and nitrogen.

[0042] Oxygen-containing functional groups are functional groups that contain oxygen but do not contain nitrogen, and examples include hydroxyl groups, ether groups, carbonyl groups, and ester groups (-COO-).

[0043] A nitrogen-containing functional group is a functional group that contains nitrogen and does not contain oxygen, for example, an amino group (-NH ２ ) are some examples.

[0044] Examples of functional groups containing oxygen and nitrogen include -N(H)COOH and >NC(=O)-.

[0045] As will be explained in more detail later, the functional groups described above are imparted to the conductive carbon layer 4 by plasma treatment. Note that the conductive carbon layer 4 may already contain oxygen-containing functional groups even before plasma treatment, but plasma treatment further imparts oxygen-containing functional groups to the conductive carbon layer 4.

[0046] The conductive carbon layer 4 is formed by sputtering, as will be described in more detail later. In other words, the conductive carbon layer 4 is preferably a sputtered layer. In addition, one side of the conductive carbon layer 4 in the thickness direction is a plasma-treated surface.

[0047] The thickness of the conductive carbon layer 4 is, for example, 1.0 nm to 20 nm, preferably 2.0 nm to 17 nm, more preferably 2.5 nm to 15 nm, even more preferably 3.0 nm to 13 nm, particularly preferably 3.5 nm to 11 nm, even more preferably 4.0 nm to 9.0 nm, and even more preferably 4.5 nm to 7.0 nm.

[0048] More specifically, the thickness of the conductive carbon layer 4 is, for example, 1.0 nm or more, preferably 2.0 nm or more, more preferably 2.5 nm or more, even more preferably 3.0 nm or more, particularly preferably 3.5 nm or more, even more preferably 4.0 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, it 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 9.0 nm or less, and even more preferably 7.0 nm or less.

[0049] Furthermore, electrode 1 satisfies the following equation (1): 0.30 < N / O < 4.00 (1) (In the above equation (1), N represents the nitrogen atom content in the conductive carbon layer measured by X-ray photoelectron spectroscopy with a photoelectron extraction angle of 90° to one side in the thickness direction of the conductive carbon layer 4, and O represents the oxygen atom content in the conductive carbon layer measured by X-ray photoelectron spectroscopy with a photoelectron extraction angle of 90° to one side in the thickness direction of the conductive carbon layer 4.)

[0050] In other words, the "N / O" ratio is greater than 0.30 but less than 4.00.

[0051] If electrode 1 satisfies the above formula (1), its long-term storage capability and activity against the test substance (described later) can be improved. Specifically, if the "N / O" ratio exceeds 0.30, long-term storage capability is improved. Also, if the "N / O" ratio is less than 4.00, activity against the test substance (described later) is improved.

[0052] On the other hand, if electrode 1 does not satisfy the above formula (1), its long-term storage capability and activity against the test substance (described later) will decrease. Specifically, if the "N / O" ratio is 0.30 or less, the long-term storage capability will decrease. Also, if the "N / O" ratio is 4.00 or more, the activity against the test substance (described later) will decrease.

[0053] The "N / O" ratio is preferably 0.40 to 3.00, more preferably 0.50 to 2.00, even more preferably 0.60 to 1.50, and most preferably 0.70 to 1.00.

[0054] More specifically, the N / O ratio is preferably 0.40 or higher, more preferably 0.50 or higher, even more preferably 0.60 or higher, and particularly preferably 0.70 or higher, from the viewpoint of improving long-term storage properties. Furthermore, from the viewpoint of improving activity against the test substance (described later), it is preferably 3.00 or lower, more preferably 2.00 or lower, even more preferably 1.50 or lower, and particularly preferably 1.00 or lower.

[0055] Furthermore, electrode 1 preferably satisfies the following formula (2): 0.100 < O / C (2) (In formula (2) above, O represents the oxygen atom content in the conductive carbon layer measured by X-ray photoelectron spectroscopy with a photoelectron extraction angle of 90° to one side in the thickness direction of the conductive carbon layer 4, and C represents the carbon atom content in the conductive carbon layer measured by X-ray photoelectron spectroscopy with a photoelectron extraction angle of 90° to one side in the thickness direction of the conductive carbon layer 4.)

[0056] In other words, the O / C ratio exceeds, for example, 0.100. When the O / C ratio exceeds 0.100, the activity against the test substance (described later) improves.

[0057] More specifically, the O / C ratio is, from the viewpoint of improving activity against the test substance (described later), for example, greater than 0.100, preferably 0.150 or higher, more preferably 0.190 or higher, and also from the viewpoint of improving activity against the test substance (described later), for example, 0.350 or lower, preferably 0.300 or lower, more preferably 0.250 or lower, and even more preferably 0.220 or lower.

[0058] The ratio (N / C) of the nitrogen atom (N) content in the conductive carbon layer to the carbon atom (C) content in the conductive carbon layer, as measured by X-ray photoelectron spectroscopy, is, for example, 0.020 to 0.500, preferably 0.080 to 0.450, more preferably 0.100 to 0.400, and even more preferably 0.120 to 0.200.

[0059] More specifically, the above ratio (N / C) is, from the viewpoint of long-term storage, for example, 0.020 or higher, preferably 0.080 or higher, more preferably 0.100 or higher, and even more preferably 0.120 or higher. Furthermore, from the viewpoint of improving the activity against the test substance (described later), it is, for example, 0.500 or lower, preferably 0.450 or lower, more preferably 0.400 or lower, and even more preferably 0.200 or lower.

[0060] The nitrogen atom content in the conductive carbon layer, as measured by X-ray photoelectron spectroscopy, is, for example, 5.0 atomic% to 30.0 atomic%, preferably 7.0 atomic% to 26.0 atomic%, more preferably 8.0 atomic% to 20.0 atomic%, and even more preferably 9.0 atomic% to 15.0 atomic%.

[0061] More specifically, the nitrogen atom content is, from the viewpoint of improving activity against the test substance (described later), for example, 5.0 atomic% or more, preferably 7.0 atomic% or more, more preferably 8.0 atomic% or more, and even more preferably 9.0 atomic% or more. Furthermore, from the viewpoint of long-term storage, it is, for example, 30.0 atomic% or less, preferably 26.0 atomic% or less, more preferably 20.0 atomic% or less, and even more preferably 15.0 atomic% or less.

[0062] The oxygen atom content in the conductive carbon layer, as measured by X-ray photoelectron spectroscopy, is, for example, 10.0 atomic% to 20.0 atomic%, preferably 11.0 atomic% to 16.0 atomic%, and more preferably 13.0 atomic% to 15.0 atomic%.

[0063] More specifically, the oxygen atom content is, for example, 10.0 atomic% or more, preferably 11.0 atomic% or more, and more preferably 13.0 atomic% or more, from the viewpoint of improving activity against the test substance (described later), and from the viewpoint of long-term storage, for example, 20.0 atomic% or less, preferably 16.0 atomic% or less, and more preferably 15.0 atomic% or less.

[0064] The carbon atom content in the conductive carbon layer, as measured by X-ray photoelectron spectroscopy, is 50.0 atomic% to 80.0 atomic%, preferably 60.0 atomic% to 75.0 atomic%, and more preferably 70.0 atomic% to 73.0 atomic%.

[0065] The nitrogen atom (N) content, oxygen atom (O) content, and carbon atom (C) content in the conductive carbon layer, as measured by the above-mentioned X-ray photoelectron spectroscopy, are adjusted by adjusting the plasma treatment conditions in the plasma treatment process described later (for example, oxygen concentration, nitrogen concentration, oxygen gas pressure, nitrogen gas pressure, plasma generation method, discharge power, and plasma time).

[0066] The measurement conditions for X-ray photoelectron spectroscopy will be described in detail in the examples below.

[0067] <Method of manufacturing electrodes> The method of manufacturing electrode 1 will be explained with reference to Figures 2A to 2D.

[0068] The method for manufacturing the electrode 1 comprises a preparation step of preparing a base film 2, a metal base layer placement step of placing a metal base layer 3 on one side of the base film 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 to manufacture a laminate 10, and a plasma treatment step of performing plasma treatment on one side of the laminate 10 in the thickness direction in the presence of oxygen gas and nitrogen gas. 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.

[0069] [Preparation Step] In the preparation step, the base film 2 is prepared as shown in Figure 2A.

[0070] [Metal Substrate Placement Process] In the metal substrate placement process, as shown in Figure 2B, the metal substrate 3 is placed on one side in the thickness direction of the base film 2.

[0071] 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.

[0072] Examples of dry methods include PVD (Physical Vapor Deposition) and CVD (Chemical Vapor Deposition). PVD is preferred as a dry method. Examples of PVD methods include sputtering (e.g., magnetron sputtering (magnetron DC discharge or magnetron DC pulsed discharge)), vacuum deposition, laser deposition, and ion plating. Sputtering is preferred as the PVD method.

[0073] In the sputtering method, a target (material for the metal underlayment 3) and a base film 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 onto the surface (one side in the thickness direction) of the base film 2 to form the metal underlayment 3.

[0074] Examples of sputtering gases include inert gases (such as argon gas).

[0075] 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.

[0076] 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.

[0077] 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.

[0078] The temperature of the base film 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.

[0079] This places the metal underlayer 3 on one side of the base film 2 in the thickness direction.

[0080] [Conductive Carbon Layer Arrangement Process] In the conductive carbon layer arrangement process, as shown in Figure 2C, a conductive carbon layer 4 is arranged on one side in the thickness direction of the metal substrate layer 3 to manufacture the laminate 10. In other words, in the conductive carbon layer arrangement process, a conductive carbon layer 4 is arranged on one side in the thickness direction of the base film 2 to manufacture the laminate 10.

[0081] The method for forming the conductive carbon layer 4 is the same as the method for forming the metal underlayer 3 described above. Preferably, the method for forming the conductive carbon layer 4 is sputtering (for example, magnetron sputtering (magnetron DC discharge or magnetron DC pulsed discharge)).

[0082] In the sputtering method, sintered carbon is selected as the target.

[0083] Examples of sputtering gases include inert gases (such as argon gas).

[0084] Furthermore, in the conductive carbon layer placement process, a reactive gas (e.g., oxygen gas) can be introduced along with the sputtering gas.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] The temperature of the base film 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.

[0089] This allows a conductive carbon layer 4 to be placed on one side in the thickness direction of the metal underlayer 3 to manufacture the laminate 10.

[0090] [Plasma Treatment Process] In the plasma treatment process, as shown in Figure 2D, plasma treatment is performed on one side in the thickness direction of the laminate 10 (specifically, one side in the thickness direction of the conductive carbon layer 4) in the presence of oxygen gas and nitrogen gas.

[0091] Specifically, the laminate 10 is transported into the vacuum chamber, and oxygen and nitrogen are supplied into the vacuum chamber.

[0092] The oxygen concentration in the vacuum chamber is, for example, 15% to 90% by volume, preferably 60% to 80% by volume.

[0093] The nitrogen concentration in the vacuum chamber is, for example, 10% to 85% by volume, preferably 20% to 40% by volume.

[0094] Furthermore, a gas other than oxygen and nitrogen (specifically, an inert gas) may be introduced into the vacuum chamber. For example, argon can be used as an inert gas. The proportion of the gas other than oxygen and nitrogen in the vacuum chamber is the remainder of the oxygen and nitrogen in the vacuum chamber, for example, 10% by volume or less.

[0095] The pressure of the oxygen gas in the vacuum chamber is, for example, 0.05 Pa to 1.00 Pa, preferably 0.10 Pa to 0.80 Pa, and more preferably 0.30 Pa to 0.70 Pa. This pressure can be adjusted by the amount of oxygen supplied to the vacuum chamber.

[0096] The pressure of the nitrogen gas in the vacuum chamber is, for example, 0.05 Pa to 1.00 Pa, preferably 0.10 Pa to 0.80 Pa, and more preferably 0.30 Pa to 0.70 Pa. This pressure can be adjusted by the amount of nitrogen supplied to the vacuum chamber.

[0097] The ratio of the oxygen gas pressure to the nitrogen gas pressure (oxygen gas pressure / nitrogen gas pressure) is, for example, 0.20 to 5.00, preferably 0.50 to 4.00, more preferably 0.60 to 3.00, even more preferably 0.70 to 2.00, and most preferably 1.00 to 1.50.

[0098] Next, plasma treatment is performed on one surface in the thickness direction of the laminate 10.

[0099] Examples of plasma generation methods include alternating current (AC) plasma generation and direct current (DC) plasma generation. Examples of AC plasma generation methods include capacitively coupled plasma (CCP), inductively coupled plasma (ICP), and surface acoustic wave (SWP). An example of DC plasma generation method is magnetron DC discharge. Preferably, a DC plasma generation method is used.

[0100] The discharge power is, for example, 1.0 W / cm². ２ ~12.0 W / cm ２ Preferably, 1.5 W / cm² ２ ~10.0 W / cm ２ Comfortable, 2.0 W / cm² ２ ~6.0 W / cm ２ More preferably, 2.5 W / cm ２ ~3.0 W / cm ２ That is the case.

[0101] The plasma processing time is, for example, 0.3 seconds to 60 seconds, preferably 1 second to 45 seconds, more preferably 10 seconds to 30 seconds, and even more preferably 20 seconds to 28 seconds.

[0102] This process involves applying plasma treatment to one surface in the thickness direction of the laminate 10 to manufacture the electrode 1. In Figure 2D, the plasma-treated surface is shown with a thick line.

[0103] Electrode 1 satisfies the above formula (1). Therefore, its long-term storage capability and activity against the test substance (ferrocyanine compound) are improved.

[0104] 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.

[0105] 2. 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.

[0106] The blood glucose sensor is equipped with an electrode 1 and a reagent layer arranged sequentially in one direction in the thickness direction.

[0107] The reagent layer contains an enzyme and a ferricyanine compound or a ferrocyanine compound.

[0108] An example of an enzyme is glucose oxidase.

[0109] Examples of ferricyanide compounds include potassium ferricyanide and sodium ferricyanide. Potassium ferricyanide is preferred as the ferricyanide compound.

[0110] Examples of ferrocyanide compounds include potassium ferrocyanide and sodium ferrocyanide.

[0111] 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.

[0112] 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.

[0113] Next, a voltage is applied to the blood glucose sensor. This causes potassium ferrocyanide to oxidize to potassium ferricyanide.

[0114] By measuring the current flowing during the above oxidation reaction, glucose in the blood can be indirectly detected.

[0115] The blood glucose sensor is equipped with an electrode 1. Therefore, it offers excellent long-term storage capabilities and activity for the test substance.

[0116] 3. The effect electrode 1 satisfies the above formula (1). Therefore, it has excellent long-term storage properties and activity for the test substance.

[0117] In more detail, the conductive carbon layer 4 is subjected to plasma treatment from the viewpoint of improving its activity against ferrocyanine compounds.

[0118] As a result, the above-mentioned functional groups (oxygen-containing functional group 20, nitrogen-containing functional group 21, and oxygen and nitrogen-containing functional group 22) are imparted to one side in the thickness direction of the conductive carbon layer 4.

[0119] First, the oxygen-containing functional group 20 has two lone pairs of electrons. These lone pairs of electrons allow for electron transfer with the ferrocyanine compound, thereby improving its activity (electron transfer capability with the ferrocyanine compound) towards the test substance (specifically, the ferrocyanine compound).

[0120] On the other hand, as shown in Figure 3A, among the oxygen-containing functional groups 20, for example, hydroxyl groups, after a long period of time following plasma treatment, invert toward the other side in the thickness direction of the conductive carbon layer 4. As a result, the lone pairs of electrons move to the other side in the thickness direction of the conductive carbon layer 4, reducing the activity of the test substance (specifically, the ferrocyanine compound). In other words, in such cases, the long-term storage capability decreases.

[0121] In other words, the more oxygen-containing functional groups 20 there are in the conductive carbon layer 4, the greater the proportion of functional groups whose activity decreases due to the above-mentioned adduction (e.g., hydroxyl groups). This improves the activity of the ferrocyanine compound immediately after plasma treatment, but if a long period of time passes after plasma treatment, the activity of the test substance (specifically, the ferrocyanine compound) decreases (long-term storage capacity decreases).

[0122] Next, although the nitrogen-containing functional group 21 has one lone pair of electrons, it is presumed that as the amount of nitrogen-containing functional group 21 increases, it inhibits the activity of the oxygen-containing functional group 20. Therefore, in the conductive carbon layer 4, the more nitrogen-containing functional group 21 there is, the lower the activity of the test substance (specifically, the ferrocyanine compound) immediately after plasma treatment. Also, as shown in Figure 3B, the nitrogen-containing functional group 21, like the oxygen-containing functional group 20, inverts inwards toward other directions in the thickness direction of the conductive carbon layer 4 after a long period of time has elapsed since plasma treatment. In other words, even after a long period of time has elapsed since plasma treatment, the activity of the test substance (specifically, the ferrocyanine compound) remains low.

[0123] Next, the functional group 22 containing oxygen and nitrogen has two or more lone pairs of electrons. Therefore, its activity towards the test substance (specifically, ferrocyanine compounds) can be improved.

[0124] Furthermore, as shown in Figure 3C, the functional group 22 containing oxygen and nitrogen has a peptide bond (amide bond), so adduction does not occur even after a long period of time has elapsed since plasma treatment. Therefore, even after a long period of time has elapsed since plasma treatment, the decrease in activity for the test substance (specifically, ferrocyanine compounds) can be suppressed.

[0125] In other words, the more functional groups 22 containing oxygen and nitrogen there are in the conductive carbon layer 4, the better the activity with respect to the test substance (specifically, ferrocyanine compounds) immediately after plasma treatment, and the better the reduction in activity with respect to the test substance (specifically, ferrocyanine compounds) can be suppressed even after a long period of time has passed since plasma treatment (excellent long-term storage performance).

[0126] Furthermore, electrode 1 satisfies the above equation (1). In other words, electrode 1 is adjusted so that the ratio (N / O) is greater than 0.30 and less than 4.00.

[0127] The ratio (N / O) is, in other words, an indicator of the amount of oxygen and nitrogen-containing functional groups 22 in the conductive carbon layer 4. If the ratio (N / O) is within the above range, the amount of oxygen and nitrogen-containing functional groups 22 is adjusted. This makes it possible to achieve both long-term storage and activity for the test substance (specifically, ferrocyanine compounds).

[0128] On the other hand, if the ratio (N / O) is less than 0.30, the amount of functional groups 22 containing oxygen and nitrogen decreases, while the amount of functional groups 20 containing oxygen increases excessively. This reduces the long-term storage capacity.

[0129] Furthermore, if the ratio (N / O) is 4.00 or higher, the amount of functional groups 22 containing oxygen and nitrogen decreases, while the amount of functional groups 21 containing nitrogen becomes excessively high. This results in a decrease in activity toward the test substance (specifically, ferrocyanine compounds).

[0130] Furthermore, regarding the long-term storage capabilities of electrode 1, specifically, even after plasma treatment, for example, one day or more, preferably seven days or more, more preferably 14 days or more, even more preferably 100 days or more, particularly preferably one year or more, and most preferably two years or more, electrode 1 retains activity toward the test substance (specifically, ferrocyanine compounds). As a result, when electrode 1 is used in a biosensor, the shelf life of the biosensor can be extended.

[0131] The blood glucose sensor is equipped with an electrode 1. Therefore, it has excellent long-term storage properties for its activity against the test substance (specifically, ferrocyanine compounds), and its shelf life can be extended.

[0132] <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.

[0133] In the above description, the electrode 1 comprises a base film 2, a metal underlayer 3, and a conductive carbon layer 4 in order toward one side in the thickness direction. However, the electrode 1 does not necessarily have to include the metal underlayer 3. In such cases, the electrode 1 comprises a base film 2 and a conductive carbon layer 4 in order toward one side in the thickness direction. Preferably, the electrode 1 includes the metal underlayer 3 from the viewpoint of improving the activity toward the substance to be tested (specifically, a ferrocyanine compound).

[0134] The electrode 1 may also include other layers (e.g., a hard coat layer, a gas barrier layer) besides the base film 2, the metal underlayer 3, and the conductive carbon layer 4. More specifically, the electrode 1 may include other layers on other surfaces in the thickness direction of the base film 2, between the base film 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.

[0135] 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 side in the thickness direction and / or the other side in the thickness direction of the base film 2.

[0136] Furthermore, if the electrode 1 includes other layers, the thickness of the base film 2 is the thickness of the electrode 1 (μm) minus the thickness of the metal underlayer 3 (nm), the thickness of the conductive carbon layer 4 (nm), and the thickness of the other layers (nm).

[0137] 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).

[0138] 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.

[0139] <Electrode Manufacturing> Example 1 [Preparation Process] A film made of polyethylene terephthalate (thickness: 188 μm) was prepared as the base film. The following process was carried out using a roll-to-roll method.

[0140] [Metal Substrate Placement Process] A niobium layer (20 nm thick) was placed on one side of the substrate film in the thickness direction using magnetron sputtering (magnetron DC discharge). The conditions for magnetron sputtering were as follows: {Conditions} Target: Niobium Sputtering Gas: Argon Gas Transport Speed: 1.5 m / min Film Formation Pressure: 0.20 Pa Discharge Power: 3.6 W / cm ２ Film forming temperature: 40℃

[0141] [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. This produced a laminate. {Conditions} Target: Sintered carbon Sputtering gas: Argon gas Transport speed: 1.5 m / min Film deposition pressure: 0.20 Pa Discharge power: 7.8 W / cm ２ Film forming temperature: 40℃

[0142] [Plasma Treatment Process] Plasma treatment was performed on one side of the laminate in the thickness direction (specifically, one side of the conductive carbon layer in the thickness direction) in the presence of oxygen and nitrogen gases, based on the following conditions. Electrodes were manufactured as a result. {Conditions} Plasma generation method: Magnetron DC discharge Gas: Oxygen and nitrogen Oxygen concentration: 56 vol% Nitrogen concentration: 44 vol% Oxygen gas pressure: 0.50 Pa Oxygen gas pressure: 0.40 Pa Discharge power: 2.6 W / cm ２ Plasma time: 24 seconds

[0143] Examples 2 to 4, Comparative Examples 1 to 3: Electrodes were manufactured according to the same procedure as in Example 1. However, the conditions of each step were changed according to Table 1. In Comparative Example 1, the plasma treatment step was not performed.

[0144] <Evaluation> [X-ray photoelectron spectroscopy measurement] The electrodes of each example and comparative example (within 12 hours of plasma treatment) were cut into 1 cm x 1 cm pieces to be used as measurement samples. Next, X-ray photoelectron spectroscopy measurements were performed on the measurement samples. Specifically, a wide scan spectrum was obtained for one side of the measurement sample in the thickness direction (the surface of the conductive carbon layer), and the elemental ratio was calculated from the ratio of the areas of each peak. Furthermore, in the narrow scan spectrum, peaks that can be attributed to C-O, C=O, and COO as oxygen-containing bonds were confirmed. From this, it is inferred that one side of the measurement sample in the thickness direction has hydroxyl groups, ether groups, carbonyl groups, and ester groups. A peak that can be attributed to C-N as a nitrogen-containing bond was confirmed. From this, it is inferred that one side of the measurement sample in the thickness direction has amino groups (-NH ２It is presumed that it has ). As for bonds containing oxygen and nitrogen, peaks that can be attributed to -N(H)COOH and >NC(=O) were confirmed. Other measurement conditions are as follows. Measurements were performed for each of the 90° photoelectron extraction angles. From this, the nitrogen atom content (atomic %), oxygen atom content (atomic %), and carbon atom content (atomic %) were determined and "N / O", "O / C", "N / C", and "(O / C)-(N / C)" were calculated. In addition, sp ３ Number of bonded atoms and sp ２ sp for the sum of the number of bonded atoms ２ Ratio and sp ３ Number of bonded atoms and sp ２ sp for the sum of the number of bonded atoms ３ The ratio was determined. The results are shown in Table 1. {Conditions} X-ray photoelectron spectrometer: Shimadzu KRATOS ULTRA2 X-ray source: Monochrome Al Kα X-ray setting: 700 μm × 300 μm [5 mA, 75 W, Resolution 20] Photoelectron extraction angle: 90 degrees relative to the sample surface Charge neutralization condition: Charge neutralization mechanism used

[0145] [Long-term storage stability of activity against ferrocyanide compounds] The activity against potassium ferrocyanide was evaluated for the electrodes of each example and comparative example immediately after plasma treatment (specifically, within 12 hours of plasma treatment).

[0146] In detail, an insulating tape with a 2 mm diameter hole was attached to one side of the conductive carbon layer 4 to create a sample electrode with a known electrode area. Cyclic voltammetry (CV) was performed using this sample electrode as the working electrode. In detail, 1 M KCl was used as the electrolyte and 1 mM KCl was used as the electrode active substance. ４ [Fe(CN)] ６The sample electrode was immersed in an aqueous solution containing potassium ferrocyanide. A silver chloride electrode was used as the reference electrode, and a platinum wire as the counter electrode. In the CV measurement, the potential was swept from negative to positive in the range of -0.1 to 0.5 V (specifically, the potential was changed in the order of -0.1 V, 0.5 V, and -0.1 V). The potential sweep rate was 0.1 V / s. The CV measurement was performed at 23°C. Three CV measurements were taken. The average value of the three ΔEp values ​​in the CV measurement was obtained as the ΔEp immediately after plasma treatment. A smaller ΔEp indicates a faster electron transfer rate and superior activity towards potassium ferrocyanide.

[0147] Next, using the same procedure, the activity of the electrodes in each example and comparative example toward potassium ferrocyanide was evaluated four weeks after plasma treatment. The results are shown in Table 1. The absolute value of the change in ΔEp from ΔEp immediately after plasma treatment to ΔEp four weeks after plasma treatment is also shown. A smaller absolute value of the change indicates better long-term storage of activity toward ferrocyanide compounds.

[0148]

[0149] 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.

[0150] 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.

[0151] 1 Electrode 2 Substrate film 4 Conductive carbon layer 10 Laminate

Claims

1. An electrode comprising a base film and a conductive carbon layer arranged sequentially toward one side in the thickness direction, satisfying the following formula (1): 0.30 < N / O < 4.00 (1) (In formula (1) above, N represents the nitrogen atom content in the conductive carbon layer measured by X-ray photoelectron spectroscopy with a photoelectron extraction angle of 90° with respect to one side in the thickness direction of the conductive carbon layer, and O represents the oxygen atom content in the conductive carbon layer measured by X-ray photoelectron spectroscopy with a photoelectron extraction angle of 90° with respect to one side in the thickness direction of the conductive carbon layer.) 2. The electrode according to claim 1, further satisfying the following formula (2): 0.100 < O / C (2) (In the above formula (2), O represents the oxygen atom content in the conductive carbon layer measured by X-ray photoelectron spectroscopy with a photoelectron extraction angle of 90° to one side in the thickness direction of the conductive carbon layer, and C represents the carbon atom content in the conductive carbon layer measured by X-ray photoelectron spectroscopy with a photoelectron extraction angle of 90° to one side in the thickness direction of the conductive carbon layer.) 3. The conductive carbon layer is, for example, sp ２ Joining and / or sp ３ The electrode according to claim 1, having a bond.

4. A biosensor comprising the electrode described in any one of claims 1 to 3.

5. A method for manufacturing an electrode according to any one of claims 1 to 3, comprising: a preparation step of preparing a base film; a conductive carbon layer arrangement step of arranging a conductive carbon layer on one side of the base film in the thickness direction to manufacture a laminate; and a plasma treatment step of performing plasma treatment on one side of the laminate in the thickness direction in the presence of oxygen gas and nitrogen gas.

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