Electrode, biosensor, and method for manufacturing electrode

Abstract

An electrode (1) comprises a base film (2) and a conductive carbon layer (4) in this order in a direction toward one side in the thickness direction. The conductive carbon layer (4) has an electron-donating group and an electron-withdrawing group on one surface in the thickness direction. The ratio of the electron-withdrawing group to the electron-donating group (electron-withdrawing group / electron-donating group), which is measured using X-ray photoelectron spectroscopy, is 70 or less. The ratio R1 of the sum of the oxygen atom content O90 and the nitrogen atom content N90 to the atom content C90 ((O90 + N90) / C90), as measured using X-ray photoelectron spectroscopy with an electron extraction angle of 90°, is 0.13 or more.

Description

Electrode, biosensor, and method for manufacturing electrode

[0001] The present invention relates to an electrode, a biosensor, and a method for manufacturing an electrode.

[0002] Conventionally, carbon electrodes have been used as electrodes for biosensors.

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

[0004] Japanese Patent Application Laid-Open No. 2021-56205

[0005] On the other hand, an example of a biosensor is a blood glucose sensor.

[0006] A blood glucose sensor is a sensor that detects glucose in the blood. The blood glucose sensor includes an electrode and a reagent layer thereon. In such a blood glucose sensor, glucose in the blood can be detected by dropping blood onto the reagent layer.

[0007] On the other hand, in the manufacture of a blood glucose sensor, an enzyme solution containing an enzyme is applied to the electrode to form a coating film, and then the coating film is cured to form a reagent layer containing the enzyme on the electrode. Therefore, from the viewpoint of productivity of the blood glucose sensor, it is required to shorten the curing time.

[0008] Furthermore, the electrodes in the blood glucose sensor are required to have improved activity against the substance to be detected.

[0009] The present invention provides an electrode, a biosensor, and a method for manufacturing an electrode that are highly productive and have excellent activity for a substance to be detected.

[0010] The present invention [1] is a method for producing a conductive carbon layer comprising a substrate film and a conductive carbon layer, which are arranged in this order toward one side in a thickness direction, the conductive carbon layer having an electron-donating group and an electron-withdrawing group on one surface in the thickness direction, the ratio of the electron-withdrawing group to the electron-donating group (electron-withdrawing group / electron-donating group) measured using X-ray photoelectron spectroscopy being 70 or less, and the atomic content C ９０Oxygen atom content O ９０ and nitrogen atom content N ９０ The ratio of the sum of R １ ((O ９０ +N ９０ ) / C ９０ ) is 0.13 or more.

[0011] The present invention [2] is characterized in that the conductive carbon layer is sp ２ Bonds and sp ３ The electrode according to the above [1] has a bond.

[0012] The present invention [3] includes a biosensor comprising the electrode according to the above [1] or [2].

[0013] The present invention [4] is a method for manufacturing an electrode according to the above [1] or [2], and includes the method for manufacturing an electrode, comprising: a preparation step of preparing a base film; a conductive carbon layer arrangement step of arranging a conductive carbon layer on one thickness-wise side of the base film to manufacture a laminate; and a plasma treatment step of performing plasma treatment on the one thickness-wise side of the laminate.

[0014] In the conductive carbon layer of the electrode of the present invention, the ratio of electron-withdrawing groups to electron-donating groups (electron-withdrawing groups / electron-donating groups), as measured by X-ray photoelectron spectroscopy, is not more than 70. Therefore, a biosensor obtained using this electrode has excellent productivity.

[0015] In addition, the atomic content C measured using X-ray photoelectron spectroscopy with a photoelectron take-off angle of 90° ９０ Oxygen atom content O ９０ and nitrogen atom content N ９０ The ratio of the sum of R １ ((O ９０ +N ９０ ) / C ９０ ) is 0.13 or more. Therefore, the activity against the target substance is excellent.

[0016] The biosensor of the present invention includes the electrode of the present invention, and therefore has excellent productivity and activity for the target substance.

[0017] The method for producing an electrode of the present invention includes a plasma treatment step of performing plasma treatment on one surface of the conductive carbon layer in the thickness direction, and therefore, in the conductive carbon layer, the ratio of electron-withdrawing groups to electron-donating groups (electron-withdrawing groups / electron-donating groups) measured by X-ray photoelectron spectroscopy is 70 or less, and the atomic content C ９０ Oxygen atom content O ９０ and nitrogen atom content N ９０ The sum of ((O ９０ +N ９０ ) / C ９０ ) ratio R １ However, it is possible to manufacture electrodes in which the σ is 0.13 or more.

[0018] Fig. 1 is a cross-sectional schematic diagram of one embodiment of an electrode of the present invention. Figs. 2A to 2D show one embodiment of a method for producing an electrode of the present invention. Fig. 2A shows a preparation step for preparing a substrate film. Fig. 2B shows a metal underlayer arranging step for arranging a metal underlayer on one surface in the thickness direction of the substrate film. Fig. 2C shows a conductive carbon layer arranging step for producing a laminate by arranging a conductive carbon layer on one surface in the thickness direction of the metal underlayer. Fig. 2D shows a plasma treatment step for performing plasma treatment on one surface in the thickness direction of the laminate.

[0019] An embodiment of the electrode of the present invention will be described with reference to FIG.

[0020] In Figure 1, the up-down direction of the paper surface is the up-down direction (thickness direction). The upper side of the paper surface is the upper side (one side in the thickness direction). The lower side of the paper surface is the lower side (the other side in the thickness direction). The left-right direction and the depth direction of the paper surface are surface directions perpendicular to the up-down direction. Specifically, they conform to the directional arrows in each figure.

[0021] 1, the electrode 1 has a 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.

[0022] The electrode 1 includes, in this order toward one side in the thickness direction, a base film 2, a metal base layer 3, and a conductive carbon layer 4. Specifically, the electrode 1 includes the base film 2, the metal base layer 3 disposed directly on the upper surface (one side in the thickness direction) of the base film 2, and the conductive carbon layer 4 disposed directly on the upper surface (one side in the thickness direction) of the metal base layer 3. The electrode 1 preferably includes the base film 2, the metal base layer 3, and the conductive carbon layer 4.

[0023] From the viewpoint of ease of handling, the thickness of the electrode 1 is, for example, 10 μm to 1000 μm, preferably 25 μm to 500 μm, more preferably 150 μm to 250 μm, even more preferably 100 μm to 225 μm, and particularly preferably 150 μm to 200 μm.

[0024] <Base Film> The base film 2 has a film shape and is the bottom layer of the electrode 1.

[0025] Examples of materials for the base film 2 include resins, ceramics, and metals. From the viewpoint of flexibility, resins are preferred as materials for the base film 2. In other words, the base film 2 is preferably a resin film.

[0026] Examples of resins include polyester resins, (meth)acrylic resins, olefin resins, polycarbonate resins, polyethersulfone resins, polyarylate resins, melamine resins, polyamide resins, polyimide resins, cellulose resins, and polystyrene resins. Examples of polyester resins include polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. Examples of (meth)acrylic resins include polymethyl methacrylate. Examples of olefin resins include polyethylene, polypropylene, and cycloolefin polymers. Examples of cellulose resins include triacetyl cellulose.

[0027] The resin is preferably a polyester resin, and more preferably polyethylene terephthalate.

[0028] The resins can be used alone or in combination of two or more.

[0029] The thickness of the substrate film 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 electrode 1 described above, and is, for example, 10 μm to 1000 μm, preferably 25 μm to 500 μm, more preferably 150 μm to 250 μm, even more preferably 100 μm to 225 μm, and particularly preferably 150 μm to 200 μm.

[0030] The thickness of the base film 2 can be measured using a dial gauge (manufactured by PEACOCK, "DG-205").

[0031] <Metallic Underlayer> The metallic underlayer 3 assists the conductivity of the conductive carbon layer 4 .

[0032] The metal underlayer 3 is disposed 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 .

[0033] The material of the metal underlayer 3 is a metal. Examples of metals include titanium, tantalum, chromium, molybdenum, tungsten, and niobium. Niobium is preferably used as the material of the metal underlayer 3 from the viewpoint of improving activity (described later) with respect to the substance to be detected. In other words, the metal underlayer 3 is preferably a niobium layer.

[0034] The material for the metal underlayer 3 can be used alone or in combination of two or more kinds.

[0035] The metal underlayer 3 is formed by sputtering, as will be described in detail later, that is, the metal underlayer 3 is preferably a sputtered layer.

[0036] The thickness of the metal underlayer 3 is, from the viewpoint of productivity by sputtering, for example, 1 nm to 200 nm, preferably 3 nm to 100 nm, and more preferably 4 nm to 80 nm; from the viewpoint of achieving both productivity and conductivity, it is even more preferably 5 nm to 50 nm, particularly preferably 7 nm to 48 nm, or even 9 nm to 45 nm; and from the viewpoint of further improving productivity and conductivity, it is even more preferably 10 nm to 40 nm, even more preferably 11 nm to 39 nm, or even more preferably 13 nm to 30 nm.

[0037] Specifically, from the viewpoint 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 4 nm or more, even more preferably 5 nm or more, particularly preferably 7 nm or more, even 9 nm or more, even 10 nm or more, even 11 nm or more, or even 13 nm or more. From the viewpoint of improving adhesion and suppressing the occurrence of cracks, the thickness is, for example, 200 nm or less, preferably 100 nm or less, more preferably 80 nm or less, even more preferably 50 nm or less, particularly preferably 48 nm or less, even 45 nm or less, even 40 nm or less, even 39 nm or less, or even 30 nm or less.

[0038] <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 base layer 3 so as to be in contact with the upper surface of the metal base layer 3. The conductive carbon layer 4 is the uppermost layer of the electrode 1.

[0039] The conductive carbon layer 4 is, for example, sp ２ Bonds and sp ３ That is, the conductive carbon layer 4 has, for example, a graphite structure and a diamond structure, which can improve the conductivity of the conductive carbon layer 4.

[0040] sp ３ Number of bonded atoms and sp ２ sp for the sum of the number of atoms bonded ３ The ratio of the number of bonded atoms (sp ３ / sp ３ +sp ２) is, for example, 0.1 to 0.9, preferably 0.2 to 0.5, more preferably 0.25 to 0.45 from the viewpoint of productivity, and even more preferably 0.30 to 0.40 from the viewpoint of electrochemical properties.

[0041] The above ratio is determined by measuring one surface of the conductive carbon layer 4 in the thickness direction by X-ray photoelectron spectroscopy. ２ Bond peak intensity and sp ３ It can be calculated based on the peak intensity of the binding.

[0042] The conductive carbon layer 4 also has an electron-donating group and an electron-withdrawing group on one surface in the thickness direction.

[0043] As will be described in detail later, the electron donating group and the electron withdrawing group are provided to one surface in the thickness direction of the conductive carbon layer 4 by plasma treatment.

[0044] Electron-donating groups include, for example, hydroxyl groups and primary amines.

[0045] Examples of the electron-withdrawing group include an ester group, a carbonyl group, and a carboxyl group. The electron-withdrawing group is preferably at least one selected from the group consisting of an ester group, a carbonyl group, and a carboxyl group.

[0046] In the electrode 1, the ratio of electron-withdrawing groups to electron-donating groups (electron-withdrawing groups / electron-donating groups) on one surface in the thickness direction of the conductive carbon layer 4, as measured by X-ray photoelectron spectroscopy, is 70 or less, preferably 50 or less, more preferably 30 or less, even more preferably 20 or less, particularly preferably 10 or less, and for example, 1 or more.

[0047] If the ratio is equal to or less than the upper limit, the curing time of the reagent layer can be shortened in the manufacture of a biosensor (specifically, a blood glucose sensor) described below, thereby improving the productivity of the biosensor.

[0048] On the other hand, if the ratio exceeds the upper limit, the curing time of the reagent layer cannot be shortened in the production of a biosensor, which will be described later, and as a result, productivity of the biosensor cannot be improved.

[0049] The ratio is adjusted to be equal to or less than the upper limit by adjusting the transport speed in the manufacturing method of the electrode 1 described later and the type and conditions of the plasma treatment described later.

[0050] In addition, the atomic content C measured using X-ray photoelectron spectroscopy with an electron take-off angle of 90° ９０ Oxygen atom content O ９０ and nitrogen atom content N ９０ The ratio of the sum of R １ ((O ９０ +N ９０ ) / C ９０ ) is 0.13 or more, preferably 0.15 or more, more preferably 0.20 or more, and, for example, 0.50 or less.

[0051] The above ratio R １ However, if the value is equal to or greater than the lower limit, the electrode 1 will have excellent activity for the target substance (specifically, excellent glucose responsiveness (described later)).

[0052] On the other hand, the above ratio R １ However, if the concentration is less than the lower limit, the activity of the electrode 1 to the target substance decreases (specifically, the glucose responsiveness (described later) decreases).

[0053] The conductive carbon layer 4 is formed by sputtering, as will be described in detail later, that is, the conductive carbon layer 4 is preferably a sputtered layer.

[0054] The thickness of the conductive carbon layer 4 is, from the viewpoint of productivity, for example, 1.0 nm to 20 nm, preferably 2.0 nm to 17 nm, and more preferably 2.5 nm to 15 nm; from the viewpoint of achieving both productivity and conductivity, it is still more preferably 3.0 nm to 13 nm, particularly preferably 3.5 nm to 11 nm, furthermore preferably 4.0 nm to 9.0 nm, or even more preferably 4.5 nm to 7.0 nm.

[0055] Specifically, from the viewpoint of improving the performance of the electrode 1, 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, further 4.0 nm or more, and even 4.5 nm or more; and from the viewpoint of ensuring adhesion to 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, further 9.0 nm or less, and even 7.0 nm or less.

[0056] <Electrode Manufacturing Method> A method for manufacturing the electrode 1 will be described with reference to FIGS. 2A to 2D.

[0057] The method for manufacturing the electrode 1 includes a preparation step of preparing a substrate film 2, a metal underlayer disposing step of disposing a metal underlayer 3 on one thickness-wise surface of the substrate film 2, a conductive carbon layer disposing step of disposing a conductive carbon layer 4 on one thickness-wise surface of the metal underlayer 3 to manufacture a laminate 10, and a plasma treatment step of subjecting one thickness-wise surface of the laminate 10 to plasma treatment. This method is preferably carried out using a roll-to-roll system. In such a case, the conveying speed is, for example, 0.1 m / min to 20.0 m / min.

[0058] [Preparation Step] In the preparation step, as shown in FIG. 2A, a base film 2 is prepared.

[0059] [Metallic Underlayer Arranging Step] In the metallic underlayer arranging step, as shown in FIG. 2B , a metallic underlayer 3 is arranged on one surface of the substrate film 2 in the thickness direction.

[0060] The metal underlayer 3 can be formed by, for example, a dry method or a wet method. The metal underlayer 3 is preferably formed by a dry method.

[0061] Examples of dry methods include PVD (physical vapor deposition) and CVD (chemical vapor deposition). Preferably, the dry method is PVD. Examples of PVD include sputtering, vacuum deposition, laser deposition, and ion plating. Preferably, the PVD is sputtering.

[0062] In the sputtering method, a target (material for the metal underlayer 3) and the substrate film 2 are placed facing each other in a vacuum chamber. Next, sputtering gas is supplied and a voltage is applied from a power source, which accelerates gas ions and irradiates them onto the target, thereby ejecting the target material from the target surface. The target material is then deposited on the surface (one surface in the thickness direction) of the substrate film 2, forming the metal underlayer 3.

[0063] The sputtering gas may be, for example, an inert gas (eg, argon gas).

[0064] The film formation pressure during sputtering is, for example, 0.05 Pa to 1.0 Pa.

[0065] The power source may be, for example, a DC power source, an AC power source, an MF power source, or an RF power source, or may be a combination of these.

[0066] The discharge power is, for example, 1.0 W / cm ２ ~12.0 W / cm ２ , preferably 1.5 W / cm ２ ~10.0 W / cm ２ is.

[0067] The temperature of the substrate film 2 (film formation temperature) is, for example, -10°C to 200°C, or preferably 20°C to 100°C.

[0068] As a result, the metal underlayer 3 is disposed on one surface of the substrate film 2 in the thickness direction.

[0069] 2C , in the conductive carbon layer arranging step, a conductive carbon layer 4 is arranged on one surface in the thickness direction of the metal base layer 3 to produce the laminate 10. In other words, in the conductive carbon layer arranging step, a conductive carbon layer 4 is arranged on one side in the thickness direction of the base film 2 to produce the laminate 10.

[0070] The method for forming the conductive carbon layer 4 is the same as the method for forming the metal underlayer 3. A preferred method for forming the conductive carbon layer 4 is sputtering.

[0071] In the sputtering method, sintered carbon is selected as the target, and the sputtering conditions (sputtering gas, deposition pressure, power supply, discharge power, and deposition temperature) in the sputtering method are the same as those in the metal underlayer disposing step described above.

[0072] In this way, the conductive carbon layer 4 is disposed on one surface in the thickness direction of the metal base layer 3, and the laminate 10 is manufactured.

[0073] [Plasma Treatment Step] In the plasma treatment step, as shown in FIG. 2D, plasma treatment is performed on one surface in the thickness direction of the laminate 10 (specifically, one surface in the thickness direction of the conductive carbon layer 4).

[0074] Examples of plasma treatments include vacuum plasma treatments in which plasma treatment is carried out under vacuum (e.g., 0.1 Pa to less than 1.0 Pa, preferably 0.2 Pa to 0.8 Pa), low-pressure plasma treatments in which plasma treatment is carried out under low pressure (e.g., 1.0 Pa to 20.0 Pa, preferably 5.0 to 15.0 Pa), and atmospheric pressure plasma treatments in which plasma treatment is carried out under atmospheric pressure.

[0075] The plasma treatment is also carried out in the presence of, for example, oxygen and / or nitrogen. Preferably, the plasma treatment is carried out in the presence of oxygen or nitrogen. In other words, the plasma treatment is carried out in the presence of oxygen (however, a trace amount of nitrogen may be unavoidably present), or the plasma treatment is carried out in the presence of nitrogen (however, a trace amount of oxygen may be unavoidably present).

[0076] Examples of such plasma treatments include vacuum plasma treatment in the presence of nitrogen, low-pressure plasma treatment in the presence of nitrogen, atmospheric pressure plasma treatment in the presence of nitrogen, low-pressure plasma treatment in the presence of oxygen, vacuum plasma treatment in the presence of oxygen, and atmospheric pressure plasma treatment in the presence of oxygen.

[0077] Specifically, the laminate 10 is transferred into a vacuum chamber, and oxygen and / or nitrogen is supplied into the vacuum chamber.

[0078] When the plasma treatment is carried out in the presence of oxygen, the oxygen concentration in the vacuum chamber is, for example, 50% by volume to 100% by volume, preferably 70% by volume to 100% by volume, and more preferably 90% by volume to 100% by volume. In practice, the oxygen concentration in the vacuum chamber is about 98% by volume.

[0079] When the plasma treatment is carried out in the presence of nitrogen, the nitrogen concentration in the vacuum chamber is, for example, 50% by volume to 100% by volume, preferably 70% by volume to 100% by volume, and more preferably 90% by volume to 100% by volume.

[0080] In addition, gases other than oxygen and nitrogen (specifically, inert gases) may be introduced into the vacuum chamber. Examples of inert gases include argon. The proportion of the other gases in the vacuum chamber is the balance of the oxygen and nitrogen in the vacuum chamber, and is, for example, 10% by volume or less.

[0081] Next, one surface of the laminate 10 in the thickness direction is subjected to plasma treatment.

[0082] Examples of plasma generation methods include alternating current plasma generation methods and direct current plasma generation methods. Examples of alternating current plasma generation methods include capacitively coupled plasma (CCP), inductively coupled plasma (ICP), and surface acoustic wave plasma (SWP). Examples of direct current plasma generation methods include magnetron DC discharge. A preferred plasma generation method is alternating current plasma generation method. A more preferred plasma generation method is capacitively coupled plasma (CCP).

[0083] The discharge power is, for example, 0.1 W / cm ２ ~12.0 W / cm ２ , preferably 2.0 W / cm ２ ~5.0 W / cm ２ , more preferably 2.5 W / cm ２ ~3.0 W / cm ２ is.

[0084] The plasma treatment time is, for example, 0.3 to 60 seconds, preferably 10 to 40 seconds, and more preferably 20 to 25 seconds.

[0085] The irradiation amount per unit time is, for example, 0.01 W / cm ２ / s to 10.0 W / cm ２ / s, preferably 0.10 W / cm ２ / s to 5.0 W / cm ２ / s.

[0086] In this way, plasma treatment is performed on one surface in the thickness direction of the laminate 10, and the electrode 1 is manufactured.

[0087] As will be described in detail later, the electrode 1 has excellent productivity and excellent activity for the target substance, and therefore, the electrode 1 can be suitably used, in particular, as an electrode in a biosensor.

[0088] Biosensors include, for example, blood glucose sensors, ketone body centers, and lactose centers.

[0089] 2. Biosensor In the following description, a blood glucose sensor will be described in detail as an example of a biosensor. In the blood glucose sensor, the test substance is, for example, a ferrocyanide compound. In the following description, the case where the test substance is a ferrocyanide compound will be described in detail.

[0090] The blood glucose sensor includes an electrode 1 and a reagent layer arranged in this order toward one side in the thickness direction.

[0091] The blood glucose sensor is manufactured by disposing a reagent layer on one surface of the electrode 1 in the thickness direction.

[0092] To arrange a reagent layer on one surface of the electrode 1 in the thickness direction, an enzyme solution is first prepared.

[0093] To prepare the enzyme solution, the enzyme, the crosslinking agent, and the ferricyanide compound or the ferrocyanide compound are mixed and dissolved in a solvent.

[0094] An example of the enzyme is glucose oxidase.

[0095] An example of a cross-linking agent is glutaraldehyde.

[0096] Examples of the ferricyanide compound include potassium ferricyanide and sodium ferricyanide. The ferricyanide compound is preferably potassium ferricyanide.

[0097] Examples of ferrocyanide compounds include potassium ferrocyanide and sodium ferrocyanide.

[0098] The solvent may be, for example, a phosphate buffer solution.

[0099] This prepares an enzyme solution.

[0100] Then, an enzyme solution is applied to one surface in the thickness direction of the electrode 1 and dried to harden the enzyme.

[0101] As drying conditions (curing conditions), the drying time (curing time) is, for example, 6 to 48 hours, or preferably 12 to 24 hours, and the drying temperature (curing temperature) is, for example, −10° C. to 30° C., or preferably 0 to 10° C.

[0102] In this way, a reagent layer is disposed on one surface in the thickness direction of the electrode 1, and a biosensor is manufactured.

[0103] A method for detecting glucose in blood using a blood glucose sensor will be described in detail below, with the reagent layer containing an enzyme and potassium ferricyanide.

[0104] In this method, blood is first added to one side of the reagent layer in the thickness direction. At this time, glucose in the blood is oxidized by the enzyme in the reagent layer. At this time, the enzyme reduces potassium ferricyanide to potassium ferrocyanide.

[0105] A voltage is then applied to the blood glucose sensor, which causes the potassium ferrocyanide to oxidize and become potassium ferricyanide.

[0106] By measuring the value of the current that flows during the oxidation reaction, glucose in the blood can be indirectly detected.

[0107] 3. Effects In the conductive carbon layer 4 of the electrode 1, the ratio of electron-withdrawing groups to electron-donating groups (electron-withdrawing groups / electron-donating groups), measured using X-ray photoelectron spectroscopy, is not more than 70. Therefore, a biosensor obtained using this electrode 1 has excellent productivity.

[0108] More specifically, as described above, in the manufacture of the blood glucose sensor, an enzyme solution is applied to one surface in the thickness direction of the electrode 1, and then dried to harden the enzyme.

[0109] From the viewpoint of improving the productivity of the electrode 1, shortening the curing time is being considered.

[0110] On the other hand, if the number of electron-withdrawing groups in the conductive carbon layer 4 of the electrode 1 increases, the electron-donating and crosslinking reaction with the crosslinking agent is inhibited, and the curing tends to be slower.

[0111] In contrast, the conductive carbon layer 4 of the electrode 1 does not contain an excessively large number of electron-withdrawing groups (specifically, the ratio of electron-withdrawing groups to electron-donating groups (electron-withdrawing groups / electron-donating groups) is 70 or less), which suppresses the above-mentioned inhibition and enables the above-mentioned curing to proceed quickly. In particular, if the electron-donating group is a hydroxyl group or a primary amine, the unpaired electron in the hydroxyl group or primary amine donates an electron to the crosslinking agent, thereby further accelerating the above-mentioned curing. As a result, the productivity of the electrode 1 can be improved.

[0112] In addition, the atomic content C of the electrode 1 measured using X-ray photoelectron spectroscopy with an electron take-off angle of 90° ９０ Oxygen atom content O ９０ and nitrogen atom content N ９０ The ratio of the sum of R １ ((O ９０ +N ９０ ) / C ９０ ) is 0.13 or more. Therefore, the activity (specifically, glucose responsiveness) with respect to the target substance can be improved. More specifically, the oxygen and nitrogen in the conductive carbon layer 4 promote the polarization of carbon, which makes it easier for the carbon to undergo an oxidation-reduction reaction with the target substance (e.g., a ferricyanide compound). As a result, it is presumed that the activity (specifically, glucose responsiveness) with respect to the target substance can be improved.

[0113] <Modifications> In the modification examples, the same components and steps as those in the first embodiment are denoted by the same reference numerals, and detailed descriptions thereof will be omitted. Furthermore, the modification examples can achieve the same effects as those in the first embodiment unless otherwise specified. Furthermore, the first embodiment and the modification examples can be combined as appropriate.

[0114] In the above description, the electrode 1 includes the base film 2, the metal underlayer 3, and the conductive carbon layer 4, in that order toward one side in the thickness direction, but the electrode 1 does not necessarily have to include the metal underlayer 3. In such a case, the electrode 1 includes the base film 2 and the conductive carbon layer 4, in that order toward one side in the thickness direction. Preferably, the electrode 1 includes the metal underlayer 3 from the viewpoint of improving activity toward the target substance.

[0115] The electrode 1 may also include layers (e.g., a hard coat layer, a gas barrier layer) other than the base film 2, the metal underlayer 3, and the conductive carbon layer 4. Specifically, the electrode 1 may include other layers on the other surface of the base film 2 in the thickness direction, 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 of the conductive carbon layer 4 in the thickness direction.

[0116] The hard coat layer is an abrasion protection layer that makes it difficult for scratches to occur on the electrode 1. Specifically, the electrode 1 preferably includes a hard coat layer on one surface and / or the other surface in the thickness direction of the substrate film 2.

[0117] Furthermore, when the electrode 1 includes other layers, the thickness of the substrate film 2 is the thickness (μm) of the electrode 1 minus the thickness (nm) of the metal underlayer 3, the thickness (nm) of the conductive carbon layer 4, and the thicknesses (nm) of the other layers.

[0118] The present invention will be described in more detail below with reference to examples and comparative examples. It should be noted that the present invention is in no way limited to these examples and comparative examples. The specific numerical values ​​of the blending ratios (content ratios), physical property values, parameters, etc. used in the following description can be replaced with the upper limit values ​​(numeric values ​​defined as "equal to or less than") or lower limit values ​​(numeric values ​​defined as "equal to or more than" or "exceeding") of the corresponding blending ratios (content ratios), physical property values, parameters, etc. described in the "Modes for Carrying Out the Invention" above.

[0119] <Manufacture of electrode> Example 1 [Preparation process] A polyethylene terephthalate film (thickness: 188 μm) was prepared as a substrate film. The following process was carried out using a roll-to-roll method. The conveying speed was 0.32 m / min.

[0120] [Metal Underlayer Forming Step] A niobium layer (thickness: 32 nm) was formed on one surface of the substrate film in the thickness direction by magnetron sputtering. The magnetron sputtering conditions were as follows: {Conditions} Target: Niobium Target power (discharge power): 1.9 W / cm ２ Sputtering gas: argon gas Film formation pressure: 0.2 Pa Film formation temperature: 40°C

[0121] [Conductive Carbon Layer Forming Step] A conductive carbon layer (thickness: 10 nm) was formed on one surface of the niobium layer in the thickness direction by magnetron sputtering. The magnetron sputtering conditions were as follows. A laminate was thus produced. {Conditions} Target: Sintered carbon Target power: 3.3 W / cm ２ Sputtering gas: argon gas Film formation pressure: 0.2 Pa Film formation temperature: 40°C

[0122] [Plasma Treatment Step] In the presence of nitrogen gas, a plasma treatment was performed on one surface in the thickness direction of the laminate (specifically, one surface in the thickness direction of the conductive carbon layer) under the following conditions. Thus, an electrode was manufactured. {Conditions} Plasma generation method: capacitively coupled plasma Nitrogen concentration: 100% by volume Gas: nitrogen Pressure: 10 ５ Pa Discharge power: 3.3W / cm ２ Plasma time: 30 seconds

[0123] Examples 2, 3, 4, Comparative Examples 1 and 2 Electrodes were manufactured based on the same procedure as in Example 1. However, the plasma treatment conditions were changed based on the information in Table 1. In Comparative Example 1, no plasma treatment was performed.

[0124] <Evaluation> [Thickness] The thickness of the metal underlayer and the conductive carbon layer in the electrodes of each Example and Comparative Example were measured by preparing cross-sectional samples for TEM by FIB microsampling and observing the cross-sections using a field emission transmission electron microscope (FE-TEM, manufactured by JOEL, "JEM-2800"). The results are shown in Table 1.

[0125] [Electron-withdrawing group / electron-donating group] The electron-withdrawing groups (ester groups, carbonyl groups, and carboxyl groups) and electron-donating groups (hydroxyl groups and primary amines) refer to the concentration of each functional group derived from the carbon layer, and are calculated as the ratio of the amount (number of moles) of each functional group to the total amount (number of moles) of carbon in the carbon layer. The concentration of each functional group can be determined using X-ray photoelectron spectroscopy (ESCA) using the gas-phase chemical modification method exemplified in Journal of Polymer Science Vol. 26 559-572 (1988) and Journal of the Adhesion Society of Japan Vol. 27 No. 4 (1991). Specifically, the values ​​are measured as follows.

[0126] The electrodes of each example and each comparative example were cut into 1 cm x 1 cm pieces to prepare measurement samples. Next, X-ray photoelectron spectroscopy was performed on the measurement samples. Specifically, narrow scan spectra of carbon, nitrogen, oxygen, and fluorine were obtained on one side of the measurement sample in the thickness direction (the surface of the conductive carbon layer), and the element ratios were calculated from the ratios of the areas of the respective peaks. Furthermore, in the C1s narrow scan spectrum, sp ２ Peaks attributable to bonds (C=C), sp ３ Peaks attributable to bonds (C-C), peaks attributable to COO and -N(H)COO, peaks attributable to C-O and C-N, and peaks attributable to C=O and >NC(=O) were confirmed. {Conditions} X-ray photoelectron spectrometer: KRATOS ULTRA2 manufactured by Shimadzu Corporation X-ray source: Monochrome Al Kα X Ray setting: 700 μm x 300 μm [5 mA, 75 W, Resolution 20] Photoelectron take-off angle: 90 degrees to the sample surface Charge neutralization conditions: Charge neutralization mechanism used

[0127] In the analysis, ESCApe was used as fitting software.

[0128] Also, sp ２ Peaks attributable to bonds (C=C), sp ３ The tops of the peaks attributable to bonds (C-C), COO and -N(H)COO, CO and C-N, and C=O and >NC(=O) were assigned as follows: ２ Peak attributable to bond (C═C): ​​284.0 eV to 284.5 eV sp ３ Peak attributable to a bond (C-C): 285.0 eV Peak attributable to C-O and C-N: 286.0 eV to 287.0 eV Peak attributable to C=O and >NC(=O): 287.3 eV to 288.2 eV Peak attributable to COO and -N(H)COO: 288.3 eV to 289.2 eV

[0129] The half-width is sp ２ The other peaks were set to about 1.1 to 1.4 times the original value. Fitting was performed within the above range so that the difference between the actual measurement and the fitting was minimized.

[0130] (Method for calculating carbonyl group concentration) The carbon atom ratio [C 未修飾 ] and the bond ratio of C=O and >NC(=O) [C=O 結合比率 ] and the carbonyl group concentration [C Ｃ=Ｏ ] was calculated based on the following formula (1): Ｃ＝Ｏ ]=[C=O 結合比率 ]×[C 未修飾 ] (1)

[0131] (Method for calculating carboxyl group concentration) Narrow scan spectra were obtained by ESCA for a sample that had been subjected to gas-phase chemical modification with a labeling reagent (trifluoroethanol) and an unmodified sample. The concentration [F ＣＯＯＨ（修飾） ], [F ＣＯＯＨ（未修飾）The carboxyl group concentration on the sample surface [C ＣＯＯＨ ] was calculated based on the following formula (2): ＣＯＯＨ ] = ([F ＣＯＯＨ（修飾） ]-[F ＣＯＯＨ（未修飾） ]) ÷ 3 (2)

[0132] (Method for calculating the ester group concentration) The carbon atom ratio [C 未修飾 ], the COO bond ratio obtained from waveform separation of narrow scan spectra [COO 結合比率 ] to determine the ester group concentration [C ＣＯＯＣ ] was calculated based on the following formula (3): ＣＯＯＣ ] = [COO 結合比率 ]×[C 未修飾 ]-[C ＣＯＯＨ ] (3)

[0133] (Method for calculating hydroxyl group concentration) Narrow scan spectra of ESCA were obtained for a sample that had been subjected to gas-phase chemical modification with a labeling reagent (trifluoroacetic anhydride) and an unmodified sample. The concentration [F Ｃ－ＯＨ（修飾） ], [F Ｃ－ＯＨ（未修飾） The hydroxyl group concentration on the sample surface [C Ｃ－ＯＨ ] was calculated based on the following formula (4): Ｃ－ＯＨ ] = ([F Ｃ－ＯＨ（修飾） ]-[F Ｃ－ＯＨ（未修飾） ]) ÷ 3 (4)

[0134] (Method for calculating primary amine concentration) Narrow scan spectra of ESCA were obtained for a sample that had been subjected to gas-phase chemical modification with a labeling reagent (pentafluorobenzaldehyde) and an unmodified sample. The concentration [F ＮＨ２（修飾） ], [F ＮＨ２（未修飾） The primary amine concentration on the sample surface [C ＮＨ２ ] was calculated based on the following formula (5): ＮＨ２ ] = ([F ＮＨ２（修飾） ]-[F ＮＨ２（未修飾） ]) ÷ 5 (5)

[0135] From the above, the electron-withdrawing groups (ester groups, carbonyl groups, and carboxyl groups) and electron-donating groups (hydroxyl groups and primary amines) were quantified, and the "electron-withdrawing groups / electron-donating groups" ratio was calculated. The results are shown in Table 1.

[0136] [The carbon atom content C on one surface in the thickness direction of the conductive carbon layer measured using X-ray photoelectron spectroscopy with a photoelectron take-off angle of 90°] ９０ Oxygen atom content O ９０ and nitrogen atom content N ９０ The ratio of the sum of R １ ((O ９０ +N ９０ ) / C ９０ ) )] The electrodes of each Example and Comparative Example (within 12 hours of plasma treatment) were cut into 1 cm x 1 cm pieces to prepare measurement samples. Next, X-ray photoelectron spectroscopy measurements were performed on the measurement samples. Specifically, a wide scan spectrum and a narrow scan spectrum were obtained for one surface in the thickness direction of the measurement sample (the surface of the conductive carbon layer), and the element ratio was calculated from the ratio of the areas of the respective peaks. Other measurement conditions are as follows. The measurement was performed at a photoelectron take-off angle of 90°. This resulted in the determination of "N ９０ "," "O ９０ " and "C ９０ " is calculated, and the ratio R １ ((O ９０ +N ９０ ) / C ９０ The results are shown in Table 1. {Conditions} X-ray photoelectron spectrometer: KRATOS ULTRA2 manufactured by Shimadzu Corporation X-ray source: Monochrome Al Kα X-ray setting: 700 μm × 300 μm [5 mA, 75 W, Resolution 20] Photoelectron take-off angle: 90 degrees to the sample surface Charge neutralization conditions: Charge neutralization mechanism used

[0137] <Productivity> [Evaluation of Hardening] An enzyme solution was prepared by mixing 0.8 mg of glucose dehydrogenase, 1.5 μL of a 4% by mass aqueous solution of bovine serum albumin, 1.2 μL of a 1% aqueous solution of glutaraldehyde, and 0.3 μL of a 0.05 M potassium phosphate buffer solution (pH 6.5).

[0138] Next, insulating tape with a 2 mm diameter hole was attached to one thickness-wise surface of the electrode (one thickness-wise surface of the conductive carbon layer) of each Example and Comparative Example. This exposed one thickness-wise surface of the electrode (one thickness-wise surface of the conductive carbon layer) of each Example and Comparative Example in an area corresponding to the hole in the insulating tape. Next, the enzyme solution was dropped onto the exposed surface, and the sample was stored in a refrigerator at 3°C ​​overnight or longer. This produced a biosensor comprising, in order, an electrode and an enzyme layer.

[0139] The biosensor was then immersed in 0.05 M potassium phosphate buffer (pH 6.5) for 1 minute. The curing time was evaluated based on the following criteria: {Criteria} A: The enzyme layer did not dissolve and remained. This indicates that the enzyme had cured sufficiently. B: The enzyme layer dissolved. This indicates that the enzyme had not cured sufficiently.

[0140] <Glucose Responsiveness> A 100 mM potassium ferrocyanide solution, an electrolyte prepared by adding KCl to 0.05 M phosphate buffer (pH 6.5) to make the concentration 1 M, and a 1000 mg / dL glucose solution were mixed to prepare a glucose solution having a concentration of 600 mg / dL.

[0141] Next, the biosensor prepared in the above productivity evaluation was used as a working electrode, and the working electrode was connected to a potentiostat (pocketSTAT, manufactured by IVIUM Technologies) together with a reference electrode (Ag / AgCl) and a counter electrode (Pt), to prepare an electrochemical measurement system equipped with them.

[0142] Next, 1 mL of glucose solution was spread on the working electrode for 1 minute. Then, cyclic voltammetry (CV) measurements were performed on the working electrode of these electrochemical measurement systems, with a potential sweep range of -0.2 to 0.8 V and a scan rate of 0.1 V / sec. In the CV measurements, the potential sweep started from 0 V and was swept from negative to positive in the range of -0.2 to 0.8 V (specifically, the potential was changed in the order of -0.2 V, 0.8 V, and -0.2 V). From the results of the CV measurements, the current value at 0.3 V when the potential was swept from negative to positive in the range of -0.2 to 0.8 V was taken as the glucose-responsive current. The glucose responsiveness was then evaluated based on the following criteria. The results are shown in Table 1.

[0143] A: The response current was 5 μA or more. B: The response current was less than 5 μA.

[0144]

[0145] The above invention is provided as an exemplary embodiment of the present invention, but this is merely an example and should not be interpreted as limiting. Modifications of the present invention that are obvious to those skilled in the art are intended to be included in the scope of the following claims.

[0146] The electrode, biosensor, and electrode manufacturing method of the present invention can be suitably used, for example, in the manufacture of a blood glucose level sensor.

[0147] REFERENCE SIGNS LIST 1 Electrode 2 Substrate film 3 Metal underlayer 4 Conductive carbon layer 10 Laminate

Claims

1. A substrate film and a conductive carbon layer are provided in this order toward one side in a thickness direction, wherein the conductive carbon layer has an electron-donating group and an electron-withdrawing group on one surface in the thickness direction, the ratio of the electron-withdrawing group to the electron-donating group (electron-withdrawing group / electron-donating group) measured using X-ray photoelectron spectroscopy is 70 or less, and the atomic content C measured using X-ray photoelectron spectroscopy with a photoelectron take-off angle of 90° is ９０ Oxygen atom content O ９０ and nitrogen atom content N ９０ The ratio of the sum of R １ ((O ９０ +N ９０ ) / C ９０ ) is 0.13 or more.

2. The conductive carbon layer is sp ２ Bonds and sp ３ The electrode of claim 1 having a bond.

3. A biosensor comprising the electrode according to claim 1 or 2.

4. A method for manufacturing an electrode according to claim 1 or 2, comprising: a preparation step of preparing a substrate film; a conductive carbon layer arrangement step of arranging a conductive carbon layer on one thickness-wise side of the substrate film to manufacture a laminate; and a plasma treatment step of performing plasma treatment on the one thickness-wise side of the laminate.

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