JP2000314714A - Electrode, manufacture thereof, and electrochemical sensor using the electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon coated electrode used as an electrochemuical sensor with a wide potential aperture and low residual current and background current by coating the pore parts of a porous body on a conductive film disposed on a base, with a carbon film. SOLUTION: A porous body 4 is provided on a conductive film 2 disposed on a base 1, and the pore parts of the porous body 4 are coated with a carbon film 6. The carbon film 6 and conductive film 2 are electrically connected by conductive buses 5. A current can therefore flow to the carbon film 6 from both upper and lower sides of the base 1. The base 1 is formed of a conductive base made of a metallic single substance comprising at least one kind of metal such as Si, Pt, Au, Ni, Cu, Ag, Nb, or an alloy. The conductive film 2 is formed of material mainly composed of an element such as Nb, Ti, Ta, Zr, Hf, W or Mo. As an electrochemical sensor, at least one substance selected out of enzyme, an antibody, an antigen and a catalyst is fixed to the carbon film 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon-coated electrode applied to a detector such as a flow cell, chromatography, biosensor and the like, and an electrochemical sensor using the same.

[0002]

2. Description of the Related Art Electrochemical measurement is generally known as one of the easiest and most environmentally friendly measurement methods, and is used for detecting hydrogen ion concentration, detection of trace metal ions, and detection of trace components in a living body. ing. In other words, a method of measuring the current value accompanying the electron transfer using an electrochemical reaction is used to detect atoms, molecules, ions, etc. dissolved in a solution, and is currently used in various fields. Have been.

In order to detect the target substance more clearly in performing such a measurement, a potential window is large, the reactivity of the electrode itself is small, and a faster electron transfer reaction in a fixed area is required. I have.

As a better electrode material having the above properties, carbon has been attracting attention. Conventionally, noble metals such as gold, platinum and palladium, semiconductors such as mercury, SnI ₂ and In ₂ O ₃ , and semimetals such as classy carbon and crystalline carbon have been used as electrode materials.

[0005] Among these materials, noble metals have a high oxygen overvoltage and are hardly oxidized and dissolved, so that they can be used as measurement electrodes in a wide potential range on the oxidizing side. However, in the case of a gold electrode, in a solution containing a halogen ion, cyanide, or the like, a complex is easily formed due to complex formation, and the measurable potential range is reduced. In addition, noble metals have a drawback that they are difficult to use for measurement on the reduction side due to a small hydrogen overvoltage, and thus their use is limited.

On the other hand, a mercury electrode has a large hydrogen overvoltage and is suitable for measurement on the reduction side, but cannot be used for measurement of an oxidation reaction because dissolution occurs on the oxidation side. SnI ₂ , In ₂
O ₃ is used as a transparent electrode and has a considerably wide potential range that can be measured. However, on the reduction side, there is a disadvantage that the electrode is reduced to tin or indium.

A general carbon electrode has high corrosion resistance,
Since the potential window is wide on both the oxidation-reduction side, substance detection at a wide potential is possible, and it is most widely used as a sensor and a detector for chromatography. In a word, it can be actually classified into several even if it is a carbon electrode. Graphite electrodes, carbon paste electrodes, glassy carbon electrodes and the like are generally well known as typical examples. Among them, a pyrolytic graphite electrode is one of the notable carbon electrodes.However, since this electrode can have a crystalline structure in a layered manner, liquid and gas do not permeate and impurities such as metals are mixed as compared with porous graphite. Since it is small, the residual current is small. In addition, as can be said for all carbon electrodes, the potential window is wide, the price is lower than platinum electrodes, the surface can be polished and it is easily regenerated,
In addition, since the hydrogen overvoltage is small, various features are known, such as being suitable for measuring ecologically related substances.

Further, in order to obtain high orientation of carbon to be coated, there is known a method of heat-treating a mixed gas of a hydrocarbon and an inert gas at a high temperature. As the actual temperature,
When processed at an extremely high temperature of 2100 to 3600 ° C., high orientation can be obtained, but most of the base cannot withstand this temperature and is dissolved. Therefore, a decrease in the high orientation treatment temperature due to immersion in the catalyst metal can be expected. For example, Chem. Mater. , 1998, 10,
260.

Further, a carbon fiber electrode (having a diameter of several μm), which has attracted attention in recent years, is used as an electrode for a microsensor, and also for an electrode reaction during high-speed sweeping.

Among them, the microarray electrode is used for detecting the concentration of hydrogen ions in a solution, detecting trace metal ions, and measuring trace components in a living body. It is important that the electrode material used for measurement can be measured in a wide potential range. The measurable potential range, that is, the potential window differs depending on the electrode, the solvent, and the supporting electrolyte, and the electrode is ideally polarized within the range of the potential window. In the case of the most common aqueous solution system, the hydrogen overvoltage is large and the oxygen overvoltage is also large,
The condition is that the dissolution potential of the electrode is high but the potential window is wide.

Further, it is known that microelectrodes have high sensitivity and quick response at present. In addition, the response behavior of a detection electrode in flow injection or chromatography depends on the electrode shape, and the response becomes faster as the electrode size decreases. Therefore, various electrode shapes and miniaturization of the electrode have been studied. Further, an example of a carbon electrode used as a minute ring electrode on the inner wall surface of a glass capillary is disclosed in Anal. Chem. , 58 (1989), 178.
2 reported. These electrodes are effective for measuring minute areas such as in a living body, but the current value that can be detected drops to the order of nA or less, increasing noise and decreasing sensitivity during measurement, making it difficult to measure low-concentration samples. There is a problem that an electric shield is required at the time of measurement.

An example of increasing the number of working electrodes in order to improve the sensitivity of the electrodes, that is, an attempt to form an array, in which a large number of carbon fibers are sealed in a plastic such as an epoxy resin and used, is disclosed in Anal. Chem. , 61 (1989), 1
59, an example in which an insulating film is coated on a glassy carbon or crystalline carbon electrode, and then a large number of fine holes are formed by using a laser to form a large number of array electrodes. . Chem. , 62 (19
90), 1339, which have the drawback that a long time is required for producing an electrode. In particular, in the former, there is a problem in the reproducibility of response due to the fact that the distance between the electrodes cannot be accurately controlled.

However, the array electrode generally needs further improvement in order to have a large background current and to be suitable for measuring a dilute solution at a nano level.

On the other hand, application to devices having functions such as high density, high sensitivity and high efficiency by utilizing a regular pore structure at the nano level formed by anodic oxidation of aluminum has attracted attention in recent years. . As a conventional method of forming a pore structure having a regularity on a nano-order scale, a polymer-processed membrane filter, a porous glass, and the like are known. It is extremely difficult to take the formed honeycomb structure and freely change the pore diameter, the pore interval, and the pore depth. However, it is known that the above-described anodized alumina film produces a honeycomb structure arranged to some extent only by electrolysis. The distance between the pores can be regulated by the voltage at the time of anodic oxidation, and the depth of the pores can be regulated by the anodic oxidation time. The pore size is the bath composition,
It is known that it depends on bath temperature, voltage and the like. Anodized alumina films having such properties are attracting interest in various new application fields as nanostructured devices.

On the other hand, carbon nanotubes, which have been discovered after the topical stable cluster of fullerenes composed of 60 carbon atoms, have been confirmed to have many unique properties on the nanometer scale. . First, there is a change in physical properties due to chirality. It has been confirmed that carbon nanotubes without chirality are metallic and semiconductors with chirality. The gap changes depending on the size of the chirality pitch, and approaches the graphite as the diameter increases. It is a one-dimensional nano-structured crystal that can be a part of a molecular element.
It is also used as a PM probe or an electron source.
Also, intercalation of metal or the like in the tube is being studied, and application examples are being studied in various fields such as batteries using the same.

[0016]

Conventional nanostructured electrodes have the disadvantage that they result in lower background currents and lower sensitivity than previously expected.

An object of the present invention is to manufacture an electrode for detecting an electrochemical reaction in a solution system with higher sensitivity than a conventional electrode. That is, the present invention provides a carbon-coated electrode having an improved potential window, a smaller residual current, a smaller background current, a regulated structure, and an electrochemical device using the same, as compared with the electrode manufactured by the above-described conventional technology. The purpose is to provide a sensor.

[0018]

The configuration of the present invention which has been made to achieve the above object is as follows.

That is, a first aspect of the present invention is that a porous film (porous material) is provided on a conductive film disposed on a substrate, and a carbon film is formed at least in the pores of the porous material (porous material). And an electrode, wherein the carbon film and the conductive film are electrically connected.

In the electrode of the present invention, the carbon film and the conductive film are electrically connected to each other, so that a current can flow from both the upper and lower sides of the substrate to the carbon film. in this case,
It is also preferable to adopt a form in which only the inner wall in the concave portion of the porous body (porous body) is covered with a carbon film, thereby enabling highly sensitive measurement.

In particular, those having a carbon spacing of 0.3355 nm to 0.3400 nm in the carbon film exhibit extremely good characteristics with respect to a potential window, a residual current and a background current.

Nb, Ti, Ta, Zr, H
It is possible to use a material containing the elements f, W, and Mo as main components. In this case, it is preferable that the carbon film and the conductive film are connected by a conductive path.

Further, Si, Pt, Au,
It is also possible to use a material mainly containing the elements of Ni, Cu, Ag and C. In this case, the pores (recesses) of the porous body are used.
Penetrates to the conductive film, and the carbon film is a hole (nano hole)
Is preferably connected to the conductive film at the bottom.

According to a second aspect of the present invention, there is provided a method of manufacturing an electrode in which a carbon film is disposed on a porous body, wherein a material having a catalytic action on the carbon film is disposed on the porous body. Disposing the carbon film on the porous body.

In the step of disposing the carbon film on the porous body, a CVD method can be preferably used.

Further, as a material having a catalytic action on the carbon film, Fe, Ni, and Co can be preferably used, whereby the orientation of the carbon film can be improved.

A third aspect of the present invention is an electrochemical sensor using the first electrode of the present invention, wherein at least one selected from an enzyme, an antibody, an antigen, and a catalyst is immobilized on the carbon film. And an electrochemical sensor.

A fourth aspect of the present invention is the first aspect of the present invention.
And a target molecule can be electrochemically separated by the pore diameter of the hole (recess).

[0029]

FIG. 1 is a sectional view showing an embodiment of a carbon-coated electrode according to the present invention. In the figure, 1 is a substrate,
Reference numeral 2 denotes a conductive film, and 4 denotes a porous body (porous body), preferably made of alumina formed by an anodic oxidation method. 6
Is a carbon film, and 7 is a concave portion (hole).

It is preferable that the porous body 4 is made of anodized alumina prepared by anodizing because the concaves 7 having a nano-size (pore diameter) are arranged at a high density.

As the substrate 1, for example, Si, Pt, A
at least one metal such as u, Ni, Cu, Ag, Nb, etc.
A conductive substrate made of a simple metal or an alloy containing a seed can be used. In the present invention, the carbon film 6 is preferably formed using a CVD method. Therefore, it is preferable to appropriately select a substrate material in consideration of the coefficient of thermal expansion and melting at a high temperature.

When alumina nanoholes formed by anodization are used as the porous body, a metal or an alloy which forms the porous body by anodization is used as the conductive film 2 as a base. Is desirable. As a more preferable material, a material having excellent workability and being inexpensive is used. Specifically, Nb, Ti, Ta, Zr, Hf, Ge,
It is preferable to use a single substance or an alloy of W or Mo, for which the base material path 5 is confirmed at the time of Al anodic oxidation, and to connect with the carbon film 6 covering this porous body through this path 5. . The porous body in the present invention is not limited to the above-described anodic oxidation method.

In addition, Si, Pt, Au,
Ni, Cu, Ag, C, etc., which are confirmed to penetrate to the underlying material during Al anodic oxidation, are used, and the connection with the carbon film 6 covering this porous body (porous body) is made by using these pores. (Concave portion) It is also preferable to be performed at the bottom.

As for the carbon coating, for example, a method of vapor-phase carbonizing a hydrocarbon can be used. As the hydrocarbon, those which are gaseous at room temperature, such as methane, ethane, propane, ethylene, acetylene, and benzene, are more suitable.

This electrode is characterized in that the surface area is larger than the apparent electrode area due to the unevenness of the pores of the porous body. Further, since the ordering and the arrangement are performed, the actual surface area can be calculated. Furthermore, by forming the concavo-convex structure, there is a feature that the detection substance can be more clearly detected. In addition, since the electrode is a carbon-coated electrode, the residual current is small, the potential window is wide, the cost is lower than that of a platinum electrode or the like, and the hydrogen overvoltage is small. From these, it can be said that this is an effective means for measuring a dilute solution.

Further, by immobilizing an enzyme, an antibody, an antigen, a catalyst and the like on the electrode of the present invention as shown in FIG. 1, it can be suitably used as an electrochemical sensor.

The above enzymes include glucose oxidase, alkaline phosphatase, alcohol oxidase, cholesterol oxidase, diaphorase,
Galactose oxidase, choline oxidase, L-
Ascopate oxidase and the like can be mentioned.

The enzyme can be immobilized by immobilizing the enzyme by covalent bond by introducing an active substituent by surface treatment of the substrate used for producing the electrode, or by immobilizing the enzyme in the vicinity of the working electrode or between the working electrodes. A method of preparing a pattern of a polymer having a substituent on the polymer, reacting the polymer with the enzyme exemplified above, forming a pattern of a porous material such as a crosslinked product of a water-soluble polymer, and adsorbing or enzymatically enzymatically A method of immobilizing by absorption and the like can be mentioned.

[0039]

EXAMPLES Hereinafter, the structure of the electrode of the present invention will be specifically described with reference to examples. The present invention is not limited to the contents of these embodiments.

(Embodiment 1) In this embodiment, N
This is an example in which b and Al were sputtered in order, the sample was anodized, and carbon was coated to produce an electrode as shown in FIG.

Hereinafter, a method of manufacturing the electrode of this embodiment will be described with reference to FIG.

The substrate 1 of the present embodiment is 10 ⁻² Ωcm
A mirror-polished n-type single-crystal Si substrate having the following resistance value was used. The n-type is phosphorus-doped. An Nb film 2 having a thickness of 100 nm is formed on the Si substrate 1 by RF sputtering.
Was formed into a film (FIG. 2A). After that, the Al film 3 is
2 nm (FIG. 2B).

Next, anodic oxidation was performed. In this example, the solution was a 0.3 M oxalic acid aqueous solution, and the solution was kept at 17 ° C. in a thermostatic water bath. Here, the anodic oxidation voltage was DC 40 V, and the electrodes were taken from the entire back side of the Si substrate 1 so that the anodic oxidation proceeded uniformly. During the anodic oxidation step, the anodic oxidation current was monitored to detect a current indicating that the anodic oxidation proceeded from the surface of the Al film 3 and reached the Nb film 2. As the reaction progresses, Al is oxidized and becomes alumina in the insulating layer, and at the same time, holes grow (FIG. 2C). Finally, the underlying Nb film 2 was electrically connected to the upper portion by the conductive path 5 (FIG. 2D). After the anodizing treatment, cleaning with pure water and isopropyl alcohol was performed. Thereafter, the sample was immersed in a 5 wt% phosphoric acid solution for 20 to 45 minutes to perform a pore widening treatment, and the pore size of the nanohole was appropriately increased.

The sample after the pore widening treatment was placed in a tubular furnace, and was heated at a rate of 5 ° C./min to a set temperature. During the heat treatment, 2% H ₂ /98% He was always flowed at 33 sccm, and 1% C ₂ H ₂ /99% He was used as a hydrocarbon gas.
1% C ₂ H ₄ /99% He was used at a flow rate of 66 sccm. During hydrocarbon pyrolysis, a gas of 100 sccm in total flows, and the mixture ratio is C ₂ H ₄ : H ₂ : He = 1: 1: 1 ×
10 ² . 1000% in 2% H ₂ /98% He atmosphere
Temperature for 3 hours and 20 minutes and 1000 minutes for 10 minutes
, And then flowed with 1% C ₂ H ₂ /99% He for 10 minutes. Thereafter, the temperature was kept at 1000 ° C. for 1 hour, and then cooled over 3 hours and 20 minutes. As a result, as shown in FIG. 1, the carbon film 6 was coated on the alumina 4.

The surface and cross section of the sample taken out were taken as FE-SE
M (Field Emission-Scanning)
Electron Microscope: Field emission scanning electron microscope). As a result, as shown in FIG. 1, it was confirmed that the conductive path 5 grew from the Nb film 2 to the bottom of the hole and was connected to the carbon film 6 covering the nanohole surface.

Next, a process performed for using the produced carbon-coated electrode as a working electrode in an electrolytic solution is shown in FIG.
This will be described with reference to FIG.

In order to use the produced carbon-coated electrode 10 as a working electrode, first, the membrane electrode 10 was sandwiched from both sides with a conductive tape 9 manufactured by 3M. And
From above, a Kapton tape 8 processed so that the surface of the membrane electrode 10 was in contact with the solution was applied to form an insulating portion. At this time, a filament tape 7 manufactured by 3M was used to fix the Kapton tape 8. The completed state is shown in FIG.

Using the carbon-coated electrode processed as described above as a working electrode, an electrochemical measurement was performed. The reagent used here is potassium hexacyanoferrate (II) used to observe a general redox response. Specifically, 10 mM hexacyanoiron (I
I) An aqueous solution of potassium acid was used, and 1.
0 M potassium chloride was used.

Using the carbon-coated alumina membrane electrode as a working electrode and measuring the CV response, the cyclic voltammogram showed that the oxidation potential was 0.28 V, the reduction potential was 0.18 V, the oxidation peak current value was 47 mA, The reduction peak current value was observed at -44 mA.

(Example 2) A lead wire was connected to only one of the carbon-coated alumina membrane electrodes produced in the same manner as in Example 1, immersed in an aqueous solution of glucose oxidase and pyrrole, and subjected to electrolytic polymerization to give glucose oxidase. An electrode for a glucose sensor was prepared by depositing a pyrrole polymer film including the above on a carbon-coated alumina film electrode.

FIG. 5 is a schematic view of the electrochemical measurement cell and the detection device manufactured in this example. In the flow injection-amperometry detection system used in the present embodiment, the sample introduced by the injector 12 into the flow path system is allowed to flow into the flow electrolytic cell under the condition that the carrier solution is fed by the feed pump 11, and the flow rate is fixed. Potential electrolysis was performed and the electrolysis current was measured. For detection of the electrolytic current, a flow cell electrode manufactured by BAS was used. At that time, in order to efficiently electrolyze the substrate, the flow path in contact with the electrode was regulated by a gasket (insulating film) 17. In FIG. 6, 14 is a lead portion of a carbon-coated alumina membrane electrode, 15 is a reference electrode, 16 is a counter electrode,
18 is a waste liquid, 19 is a potentiostat, and 20 is a monitor.

In this embodiment, a phosphate buffer (0.1 mol
/ L, pH 6.8) by the liquid sending pump 11 to dissolve a phosphate buffer solution (0.1 mol
/ L, pH 6.8). Next, the carbon-coated alumina membrane electrode 1
When a potential of 0.6 V was applied to Sample No. 4, the oxidation potential of hydrogen peroxide generated by the action of glucose oxidase was observed. The amount of current was 1 mA per 1 mmol / l of glucose.

Further, the detection was sufficiently performed with the sample solution of 0.1 ml or less, and even in a glucose solution containing a large amount of impurities such as fructose, glucose was selectively detected without being affected by the impurities.

Example 3 Glucose oxidase was immobilized on a gauze-like substance, and the immobilized enzyme membrane was attached on a carbon-coated alumina membrane electrode produced in the same manner as in Example 1, and the same measurement as in Example 2 was carried out. Was done. As for the immobilized enzyme membrane, the enzyme was immobilized in a mesh-like place as shown in FIG.

FIG. 8 is a schematic view of a carbon-coated alumina membrane electrode manufactured in this embodiment. 21 is an immobilized enzyme membrane, 6
Is carbon, 4 is anodized alumina, 2 is an Nb film, and 1 is a Si substrate.

As for the measuring device, the electrode 1 shown in FIG.
The electrode of FIG.

In this embodiment, a KCl aqueous solution (0.1 mol
/ L) was flowed by the liquid sending pump 11, and a KCl aqueous solution (0.1 mol / l) in which glucose was dissolved at various concentrations was injected by the injector 12. Next, when a potential of 0.6 V was applied to the enzyme-modified carbon-coated alumina membrane electrode 14, the oxidation potential of hydrogen peroxide generated by the action of glucose oxidase was observed. The amount of current was 10 mA per 1 mmol / l of glucose.

Further, the detection was sufficiently performed with 0.1 ml or less of the sample solution, and even in a glucose solution containing a large amount of impurities such as fructose, glucose was selectively detected without being affected by the impurities.

[0059]

As described above, according to the present invention, the following effects can be obtained. (1) The electrode of the present invention has characteristics that the potential window is wide, the residual current and the background current are small, and it is possible to measure a dilute solution or the like. (2) The carbon film is coated only on the inner wall in the pores of the porous body (porous body), and at least a part of the conductive film has a structure electrically connected to the carbon film, so that high sensitivity is achieved. Measurement has become possible. (3) After immersing the porous body (porous body) in a substance that can serve as a catalyst, carbon was coated to improve the orientation. (4) The modified electrochemical electrode in which an enzyme, an antibody, an antigen, or a catalyst is immobilized directly on the electrode of the present invention or directly on at least a part of the surface carbon was able to be a highly sensitive electrochemical sensor. (5) In the electrode of the present invention, an electrode having characteristics such as electrochemical separation or isolation of the target molecule could be produced depending on the pore diameter of the porous body (porous body). (6) The electrode of the present invention having the above excellent properties is expected to be further applied in various fields, for example, an electric electrode usable for an ultra-sensitive molecular detector such as a flow cell, a liquid chromatography, a biosensor, and the like. Very useful as a chemical electrode.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing one configuration example of an electrode of the present invention.

FIG. 2 is a diagram for explaining a manufacturing process of the electrode of the present invention.

FIG. 3 is a diagram for explaining a preparation method for using the electrode of the present invention as a working electrode.

FIG. 4 is a diagram showing a completed state in which the electrode of the present invention is used as a working electrode.

FIG. 5 is a schematic diagram of a sample detector by a flow injection method using an electrode of the present invention.

FIG. 6 is a schematic diagram of a network material on which an enzyme is immobilized.

FIG. 7 is a cross-sectional view of the electrode of the present invention in which the immobilized enzyme membrane of FIG. 6 is adhered on carbon.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Si substrate 2 Nb film 3 Al film 4 Porous body (anodized alumina) 5 Nb (conductive path) 6 Carbon 7 Filament tape 8 Kapton tape 9 Conductive tape 10 Carbon-coated alumina film electrode 11 Liquid feed pump 12 Injector 13 Si Tube 14 working electrode (carbon-coated alumina membrane electrode) 15 reference electrode 16 counter electrode 17 gasket 18 waste liquid 19 potentiostat 20 monitor 21 immobilized enzyme membrane

Claims (12)

[Claims] An electroconductive film disposed on a substrate has a porous body, and at least a carbon film is disposed in a hole of the porous body, and the carbon film and the conductive film are electrically connected to each other. An electrode which is connected. 2. The electrode according to claim 1, wherein said porous body is made of alumina. 3. The electrode according to claim 1, wherein the porous body is formed by an anodic oxidation method. 4. The electrode according to claim 1, wherein the diameter of the hole of the porous body is nano-sized. 5. The electrode according to claim 1, wherein a plane interval of carbon constituting the carbon film is 0.3355 nm or more and 0.3400 nm or less. 6. The conductive film is made of Nb, Ti, Ta, Z.
r, Hf, W, Mo, Si, Pt, Au, Ni, Cu,
The electrode according to any one of claims 1 to 5, wherein at least one element selected from Ag and C is a main component. 7. The electrode according to claim 1, wherein the hole exposes the conductive film. 8. A method for producing an electrode in which a carbon film is disposed on a porous body, the method comprising: disposing a material having a catalytic action on the carbon film on the porous body; Arranging on the porous body. 9. The method according to claim 8, wherein the step of disposing the carbon film on the porous body is performed by a CVD method. 10. The method according to claim 8, wherein the material having a catalytic action on the carbon film is made of at least one selected from the group consisting of Fe, Ni, and Co. 11. An electrochemical sensor using the electrode according to any one of claims 1 to 7, wherein at least one selected from an enzyme, an antibody, an antigen, and a catalyst is immobilized on the carbon film. An electrochemical sensor characterized by the following. 12. An electrochemical sensor using the electrode according to any one of claims 1 to 7, wherein a target molecule can be electrochemically separated by a pore diameter of the hole. .