Electrode, biosensor, and method for manufacturing electrode

Abstract

An electrode (1) is provided with a base material film (2) and a conductive carbon layer (4), in the order in a direction toward one side in the thickness direction. The conductive carbon layer (4) has a first functional group and a second functional group on one surface in the thickness direction. The first functional group is composed of an ester group and an ether group. The second functional group is composed of a hydroxyl group, a primary amine, and a carbonyl group. The ratio (first functional group / second functional group) of the first functional group to the second functional group on one surface of the conductive carbon layer (4) in the thickness direction is 4.1 or more as determined using X-ray photoelectron spectroscopy in which the photoelectron take-off angle is 90°.

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, and more particularly to an electrode, a biosensor including the electrode, 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] Such biosensors are required to have a long shelf life depending on their applications.

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

[0007] The present invention [1] is an electrode comprising a base film and a conductive carbon layer, arranged in this order toward one side in a thickness direction, the conductive carbon layer having a first functional group and a second functional group on one surface in the thickness direction, the first functional group being an ester group and an ether group, and the second functional group being a hydroxyl group, a primary amine, and a carbonyl group, and the ratio of the first functional group to the second functional group (first functional group / second functional group) on one surface in the thickness direction of the conductive carbon layer, as measured using X-ray photoelectron spectroscopy with a photoelectron take-off angle of 90°, is 4.1 or more.

[0008] The present invention [2] includes the electrode according to the above [1], further comprising a metal underlayer between the substrate film and the conductive carbon layer.

[0009] The present invention [3] includes a biosensor comprising the electrode according to the above [1] or [2].

[0010] The present invention [4] is a method for producing the electrode according to the above [1] or [2], comprising: a preparation step of preparing a base film; a conductive carbon layer arrangement step of arranging a conductive carbon layer on one side in a thickness direction of the base film to produce a laminate; and a plasma treatment step of performing a plasma treatment on the one side in the thickness direction of the laminate in the presence of oxygen gas.

[0011] In the electrode of the present invention, the ratio of the first functional groups to the second functional groups (first functional groups / second functional groups) on one surface in the thickness direction of the conductive carbon layer, as measured by X-ray photoelectron spectroscopy with a photoelectron take-off angle of 90°, is 4.1 or more, thereby improving long-term storage stability.

[0012] The biosensor of the present invention includes the electrode of the present invention, and therefore has excellent long-term storage properties.

[0013] The method for producing an electrode of the present invention includes a plasma treatment step of performing plasma treatment on one surface of a conductive carbon layer in the thickness direction in the presence of oxygen gas, thereby producing an electrode in which the ratio of first functional groups to second functional groups (first functional groups / second functional groups) on one surface of the conductive carbon layer in the thickness direction is 4.1 or more.

[0014] FIG. 1 is a cross-sectional schematic diagram of an embodiment of an electrode of the present invention. FIGS. 2A to 2D show an 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 disposing step for disposing a metal underlayer on one thickness-wise surface of the substrate film. FIG. 2C shows a conductive carbon layer disposing step for disposing a conductive carbon layer on one thickness-wise surface of the metal underlayer to produce a laminate. FIG. 2D shows a plasma treatment step for performing plasma treatment on one thickness-wise surface of the laminate in the presence of oxygen gas. FIGS. 3A and 3B show changes in the first functional group and the second functional group after a long period of time has passed since the plasma treatment. FIG. 3A shows the first functional group after a long period of time has passed since the plasma treatment. FIG. 3B shows the second functional group after a long period of time has passed since the plasma treatment.

[0015] An embodiment of the electrode of the present invention will be described with reference to FIG.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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 50 μm to 250 μm, even more preferably 100 μm to 225 μm, and particularly preferably 150 μm to 200 μm.

[0020] <Base Film> The base film 2 has a film shape and is the bottom layer of the electrode 1.

[0021] 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.

[0022] 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.

[0023] The resin is preferably a polyester resin, and more preferably polyethylene terephthalate.

[0024] The resins can be used alone or in combination of two or more.

[0025] 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 50 μm to 250 μm, even more preferably 100 μm to 225 μm, and particularly preferably 150 μm to 200 μm.

[0026] The thickness of the base film 2 can be measured using a dial gauge (manufactured by PEACOCK, "DG-205").

[0027] <Metallic Underlayer> The metallic underlayer 3 assists the conductivity of the conductive carbon layer 4 .

[0028] The metal underlayer 3 is disposed on the entire lower surface of the conductive carbon layer 4 so as to be in contact with the lower surface of the conductive carbon layer 4. In other words, the metal underlayer 3 is disposed between the base film 2 and the conductive carbon layer 4.

[0029] 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 analyte. In other words, the metal underlayer 3 is preferably a niobium layer.

[0030] The material for the metal underlayer 3 can be used alone or in combination of two or more kinds.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] <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.

[0035] 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 and can also improve the activity (described later) of the conductive carbon layer 4 with respect to the test substance.

[0036] 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, 0.10 to 0.90, preferably 0.20 to 0.50, 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.

[0037] 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.

[0038] The conductive carbon layer 4 has a first functional group and a second functional group on one surface in the thickness direction.

[0039] As will be described in detail later, the first functional group and the second functional group are provided to one surface in the thickness direction of the conductive carbon layer 4 by plasma treatment.

[0040] The first functional group, which will be described in detail later, retains activity (described later) toward the test substance even after a long period of time has passed since the plasma treatment. The first functional group is an ester group or an ether group.

[0041] The second functional groups are hydroxyl groups, primary amines, and carbonyl groups, and lose their activity (described below) toward the test substance after a long period of time has passed since the plasma treatment, as will be described in detail later.

[0042] Furthermore, as will be described in detail later, the electrode 1 is produced by a plasma treatment step in which plasma treatment is performed in the presence of oxygen gas. Therefore, in X-ray photoelectron spectroscopy, which will be described in detail in Examples later, the amount of secondary or higher amines in the conductive carbon layer 4 is below the detection limit.

[0043] In the electrode 1, the ratio of the first functional groups to the second functional groups (first functional groups / second functional groups) on one surface in the thickness direction of the conductive carbon layer 4, measured using X-ray photoelectron spectroscopy, is 4.1 or more, preferably 4.5 or more, preferably 5.0 or more, and for example, 10.0 or less, preferably 7.0 or less, more preferably 6.0 or less.

[0044] When the ratio is equal to or greater than the lower limit, the long-term storage property is improved.

[0045] On the other hand, if the ratio is less than the lower limit, the long-term storage stability is reduced.

[0046] The ratio is adjusted to be equal to or greater than the lower limit by adjusting the transport speed in the manufacturing method of the electrode 1 described later and the plasma treatment conditions (e.g., oxygen concentration, pressure, discharge power, and plasma time) in the plasma treatment step described later.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] <Electrode Manufacturing Method> A method for manufacturing the electrode 1 will be described with reference to FIGS. 2A to 2D.

[0051] The method for producing 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 produce a laminate 10, and a plasma treatment step of performing a plasma treatment on one thickness-wise surface of the laminate 10 in the presence of oxygen gas. 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.

[0052] [Preparation Step] In the preparation step, as shown in FIG. 2A, a base film 2 is prepared.

[0053] [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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] The sputtering gas may be, for example, an inert gas (eg, argon gas).

[0058] The film formation pressure during sputtering is, for example, 0.05 Pa to 1.0 Pa.

[0059] 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.

[0060] The discharge power is, for example, 0.9 W / cm ２ ~30.0 W / cm ２ , preferably 1.0 W / cm ２ ~12.0 W / cm ２ , more preferably 1.5 W / cm ２ ~10.0 W / cm ２ , more preferably 1.6 W / cm ２ ~5.0 W / cm ２ , particularly preferably 1.7 W / cm ２ ~3.5 W / cm ２ is.

[0061] 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.

[0062] As a result, the metal underlayer 3 is disposed on one surface of the substrate film 2 in the thickness direction.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] [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) in the presence of oxygen gas.

[0068] Specifically, the laminate 10 is transferred into a vacuum chamber, and oxygen is supplied into the vacuum chamber.

[0069] 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.

[0070] A gas other than oxygen (specifically, an inert gas) may be introduced into the vacuum chamber. Examples of the inert gas include argon and nitrogen. The proportion of the gas other than oxygen in the vacuum chamber is the balance of the oxygen in the vacuum chamber, and is, for example, 10% by volume or less.

[0071] The pressure inside the vacuum chamber is, for example, 0.1 Pa to 2.0 Pa. The pressure can be adjusted by the amount of oxygen supplied to the vacuum chamber.

[0072] Next, one surface of the laminate 10 in the thickness direction is subjected to plasma treatment.

[0073] Examples of plasma generation methods include an AC plasma generation method and a DC plasma generation method. Examples of AC plasma generation methods include capacitively coupled plasma (CCP), inductively coupled plasma (ICP), and surface acoustic wave plasma (SWP). Examples of DC plasma generation methods include magnetron DC discharge. A preferred plasma generation method is a DC plasma generation method.

[0074] The discharge power is, for example, 1.0 W / cm ２ ~12.0 W / cm ２ , preferably 2.0 W / cm ２ ~5.0 W / cm ２ is.

[0075] The plasma treatment time is, for example, 0.3 seconds to 60 seconds or less, or 0.5 seconds to 30 seconds.

[0076] Specifically, the plasma treatment time is, for example, 0.3 seconds or more, preferably 0.5 seconds or more, from the viewpoint of reliably imparting the first functional group and the second functional group to one surface of the conductive carbon layer 4 in the thickness direction, and is, for example, 60 seconds or less, preferably 30 seconds or less, from the viewpoint of preventing a change in the film quality of the conductive carbon layer 4 and a decrease in the activity (described later) of the conductive carbon layer 4 against the test substance.

[0077] In this way, plasma treatment is performed on one surface in the thickness direction of the laminate 10, and the electrode 1 is manufactured.

[0078] In the electrode 1, the ratio of the first functional groups to the second functional groups (first functional groups / second functional groups) on one surface in the thickness direction of the conductive carbon layer 4, as measured by X-ray photoelectron spectroscopy, is 4.1 or more, thereby improving the long-term storage properties.

[0079] Therefore, the electrode 1 can be suitably used particularly as an electrode in a biosensor, that is, the electrode 1 is preferably a biosensor electrode.

[0080] 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.

[0081] The blood glucose sensor includes an electrode 1 and a reagent layer arranged in this order toward one side in the thickness direction.

[0082] The reagent layer contains an enzyme and a ferricyanide or ferrocyanide compound.

[0083] An example of the enzyme is glucose oxidase.

[0084] Examples of the ferricyanide compound include potassium ferricyanide and sodium ferricyanide. The ferricyanide compound is preferably potassium ferricyanide.

[0085] Examples of ferrocyanide compounds include potassium ferrocyanide and sodium ferrocyanide.

[0086] 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.

[0087] 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.

[0088] A voltage is then applied to the blood glucose sensor, which causes the potassium ferrocyanide to oxidize and become potassium ferricyanide.

[0089] By measuring the value of the current that flows during the oxidation reaction, glucose in the blood can be indirectly detected.

[0090] The blood glucose sensor includes the electrode 1. Therefore, it has excellent long-term storage properties.

[0091] 3. Effects In the electrode 1, the ratio of the first functional groups to the second functional groups (first functional groups / second functional groups) on one surface in the thickness direction of the conductive carbon layer, as measured by X-ray photoelectron spectroscopy, is 4.1 or more. Therefore, the long-term storage property is improved.

[0092] Specifically, blood glucose sensors are known as biosensors. In recent years, there has been a growing demand for people to measure their own blood glucose levels at any time in their daily lives. To achieve this, there is a demand for blood glucose sensors with a longer shelf life.

[0093] As described above, the blood glucose sensor includes an electrode 1 and a reagent layer, arranged in this order toward one side in the thickness direction. The reagent layer contains an enzyme and a ferricyanide compound or a ferrocyanide compound. Regarding a method for detecting glucose in blood using the blood glucose sensor, if the ferricyanide compound is potassium ferricyanide, the glucose in the blood is first oxidized by the enzyme in the reagent layer, and the enzyme also reduces the potassium ferricyanide to potassium ferrocyanide. Next, by applying a voltage to the blood glucose sensor, the potassium ferrocyanide is oxidized to potassium ferricyanide. Then, by measuring the current flowing during the oxidation reaction, glucose in the blood is indirectly detected.

[0094] Therefore, in order to extend the shelf life of a blood glucose sensor, it is necessary for its activity toward the test substance (electron transfer with the test substance) to be maintained for a long period of time (storage stability of activity toward the test substance).

[0095] In the electrode 1, the ratio of the first functional groups to the second functional groups (first functional groups / second functional groups) on one surface in the thickness direction of the conductive carbon layer measured by X-ray photoelectron spectroscopy is 4.1 or more, thereby improving the long-term storage stability of the activity against the test substance (ferrocyanide compound).

[0096] More specifically, the above-described plasma treatment can impart a first functional group and a second functional group to one surface in the thickness direction of the conductive carbon layer 4, but the first functional group and the second functional group will invert over a long period of time after the plasma treatment.

[0097] 3A, immediately after the plasma treatment, the ester group, which is the first functional group, is arranged so that the "-O-" in the ester group (-C(=O)-O-) faces one side in the thickness direction, but after a long period of time has passed since the plasma treatment, it rotates 180° around the axis of rotation that is the plane direction of the electrode 1. The ether group, which is the first functional group, also rotates in the same way.

[0098] Similarly, as shown in FIG. 3B , the second functional groups, hydroxyl groups, primary amines, and carbonyl groups, are arranged so that they face one side in the thickness direction immediately after plasma treatment, but after a long period of time has passed since plasma treatment, they rotate 180° around the surface direction of electrode 1 as the axis of rotation.

[0099] Next, the activity against the test substance after a long period of time has passed since the plasma treatment will be examined.

[0100] 3A, after a long period of time has passed since the plasma treatment, the lone electron pair of the first functional group faces one side in the thickness direction (toward the air side). Such lone electron pair allows electron donation and acceptance with the analyte, and it is presumed that the first functional group has excellent activity with respect to the analyte (electron donation and acceptance with the analyte).

[0101] 3B, after a long period of time has passed since the plasma treatment, the second functional groups, hydroxyl groups, primary amines, and carbonyl groups (hydrophilic groups), are oriented toward the other side in the thickness direction. As a result, one side (the air side) of the conductive carbon layer 4 contains only carbon, which is presumably less active against the test substance.

[0102] From the above, it can be seen that in the conductive carbon layer 4, if the number of first functional groups, which have excellent activity toward the test substance even after a long period of time has passed since plasma treatment, is made larger than the number of second functional groups, whose activity toward the test substance decreases after a long period of time has passed, the long-term storage stability of the activity toward the test substance can be improved.

[0103] In the electrode 1, the ratio of the first functional groups to the second functional groups (first functional groups / second functional groups) on one surface in the thickness direction of the conductive carbon layer, as measured by X-ray photoelectron spectroscopy with a photoelectron take-off angle of 90°, is 4.1 or more, thereby improving the long-term storage stability of the activity against the test substance.

[0104] Specifically, the electrode 1 retains activity against the test substance even after 1 to 72 days have passed since the plasma treatment. As a result, when the electrode 1 is used in a biosensor, the expiration date of the biosensor can be extended.

[0105] The blood glucose sensor includes the electrode 1. Therefore, the activity of the test substance can be maintained for a long period of time, and the expiration date can be extended.

[0106] <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.

[0107] In the above description, the electrode 1 includes the substrate 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 substrate 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 analyte.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] In the above explanation, electrode 1 is described as an electrode of a biosensor, but it is not limited to this and can also be used as an electrode for electrochemical measurements in which a test substance is the measurement target, specifically as a working electrode for performing cyclic voltammetry (CV).

[0112] 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.

[0113] <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.

[0114] [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

[0115] [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

[0116] [Plasma Treatment Step] In the presence of oxygen gas, 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: magnetron DC discharge Oxygen concentration: 98% by volume Gas: oxygen Pressure: 0.5 Pa Discharge power: 2.6 W / cm ２ Plasma time: 24 seconds

[0117] Examples 2 and 3 Electrodes were produced based on the same procedure as in Example 1. However, the conditions for each step were changed based on the description in Table 1. In addition, in the preparation step, a gas barrier layer (silicon layer) was disposed on one surface in the thickness direction of the substrate film using magnetron sputtering (target: silicon, sputtering gas: argon gas) according to the conditions described in Table 1.

[0118] Comparative Example 1 An electrode was produced according to the same procedure as in Example 1, except that the plasma treatment step was not carried out.

[0119] <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.

[0120] [First Functional Group / Second Functional Group] The first functional group (ester group and ether group) and the second functional group (hydroxyl group, primary amine, and carbonyl group) 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, these values ​​are measured as follows.

[0121] 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

[0122] In the analysis, ESCApe was used as fitting software.

[0123] 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

[0124] The half-width is sp ２The 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.

[0125] (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)

[0126] (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)

[0127] (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)

[0128] (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)

[0129] (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)

[0130] (Calculation method of ether group) The carbon atom ratio of the unmodified product [C 未修飾 ], and the bond ratio of C—O to C—N [C—O and C—N bond ratio] obtained from waveform separation of the narrow scan spectrum was used to determine the concentration of ether groups and secondary or higher amines on the sample surface [C ＣＯＣ，ＣＮＣ ] was calculated based on the following formula (6): ＣＯＣ，ＣＮＣ ] = [C-O and C-N bond ratio] x [C 未修飾 ]-[C Ｃ－ＯＨ ]-[C ＮＨ２ (6) In Examples 1 to 3, the plasma treatment step is carried out in the presence of oxygen gas, so the concentration of secondary or higher amines is below the detection limit.

[0131] From the above, the primary functional groups (ester groups and ether groups) and secondary functional groups (hydroxyl groups, primary amine groups and carbonyl groups) were quantified, and the "primary functional groups / secondary functional groups" ratio was calculated. The results are shown in Table 1.

[0132] [Long-term storage stability of activity against ferrocyanide compounds] Immediately after plasma treatment (specifically, within 12 hours after plasma treatment), the activity against potassium ferrocyanide was evaluated for the electrodes of each example and each comparative example.

[0133] Specifically, a sample electrode with a known electrode area was prepared by attaching an insulating tape with a hole of 2 mm diameter to one side of the conductive carbon layer 4. Cyclic voltammetry (CV) was carried out using this sample electrode as the working electrode. Specifically, 1 M KCl was used as the electrolyte and 1 mM KCl was used as the electrode active material. ４ [Fe(CN) ６ The sample electrode was immersed in an aqueous solution containing potassium ferrocyanide. 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 performed. The average value of the ΔEp values ​​obtained three times in the CV measurement was taken as ΔEp. It can be seen that the smaller the ΔEp, the faster the electron transfer rate and the better the activity against potassium ferrocyanide.

[0134] Next, using the same procedure, the activity of the electrodes of each Example and Comparative Example against potassium ferrocyanide was evaluated four weeks after the plasma treatment. The results are shown in Table 1. Table 1 also shows the absolute value of the rate of change of ΔEp relative to ΔEp immediately after the plasma treatment. It can be seen that the smaller the rate of increase, the better the long-term storage stability of the activity against ferrocyanide compounds.

[0135]

[0136] 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.

[0137] 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.

[0138] REFERENCE SIGNS LIST 1 Electrode 2 Base film layer 3 Metal underlayer 4 Conductive carbon layer 10 Laminate

Claims

1. An electrode comprising a base film and a conductive carbon layer, arranged in this order toward one side in a thickness direction, wherein the conductive carbon layer has a first functional group and a second functional group on one surface in the thickness direction, wherein the first functional groups are ester groups and ether groups, and the second functional groups are hydroxyl groups, primary amines, and carbonyl groups, and wherein the ratio of the first functional groups to the second functional groups (first functional group / second functional group) on one surface in the thickness direction of the conductive carbon layer, as measured using X-ray photoelectron spectroscopy with a photoelectron take-off angle of 90°, is 4.1 or more.

2. The electrode according to claim 1, further comprising a metal underlayer between the substrate film and the conductive carbon layer.

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

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 in the presence of oxygen gas.

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