JP2590002B2 - Microelectrode cell for electrochemical measurement and method for producing the same - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microelectrode cell for electrochemical measurement in which a comb-shaped electrode, a reference electrode and a counter electrode are integrally formed on a substrate, and a method of manufacturing the same. is there.

[Conventional technology]

Conventionally, three electrochemical measurement methods have been proposed as a method for qualitative or quantitative analysis of ions and molecules contained in water, an organic solvent, a living body, and the like. The first method is to use one electrode for detecting a substance, its counter electrode, and one reference electrode including a reference substance serving as a reference for defining an electric potential.
One electrode is connected to a measuring instrument such as a potentiostat. In the second method, an intermediate or active species generated by an electrochemical reaction is detected, and the working electrode is used as two electrodes in order to investigate a reaction mechanism. A rotating ring / disk electrode for detecting active species and intermediates is used.
FIG. 3 is a principle diagram showing detection of active species by this method.
It comprises a rotating ring / disk electrode 31 and a ring electrode 32 surrounding the electrode 31 at a fixed distance. By rotating the ring electrode 32 around the disk electrode 31, a flow 33 of the solution to be measured is generated, and the electrolyte in the solution is transported in the direction of the solution layer, the disk electrode, and the ring electrode. As a result, the reduced form (Red) of the electrolyte is deprived of the electric charge e ⁻ by the disk electrode 31, and becomes an oxidized form (Ox) as an active species. Next, the generated oxidant (Ox) is again given a charge e ⁻ by the ring electrode 32 to become a reductant (Red) again, and the charge e ⁻ due to the active species.
Is performed. Therefore, by changing the potential between the disk electrode 31 and the ring electrode 32, the anti-intermediate of the active species generated at the disk electrode 31 can be detected at the ring electrode 32, and information on them can be obtained. The third approach is
A microelectrode is used as a means for performing an electrochemical measurement of a microregion. It has a pair of electrodes, and many applications to biometric electrodes, biosensors and the like have been proposed. In addition, in recent years, application of lithography technology has been proposed as a method for manufacturing a microelectrode. In this method, a resist is applied to a substrate, an image mask having an electrode pattern is overlaid, exposed, and developed, and then a metal thin film is formed by an evaporation method or the like. Then, the resist is peeled off to obtain minute electrodes on the substrate. According to this method, a large number of microelectrodes having an arbitrary shape and a constant interelectrode distance can be formed on a substrate with high reproducibility. The present invention can be applied to a similar electrode pair capable of measurement, a base electrode of an electrochemical device, a sensor and the like. By applying the microelectrode manufacturing method, a microelectrochemical transistor (for example, J. Phya. Chem. 89, 5133 (1985)), a low-molecular or high-molecular complex using a comb-shaped platinum electrode has been developed. Chemical measurements (Anal. Chem., 58, 601 (1986)) and the like have been performed.

[Problems to be solved by the invention]

However, each of the three conventional electrochemical measurement methods has the following disadvantages. First, the first method is
The substance to be detected such as ions and molecules in the solution can be directly detected, but it is difficult to electrochemically react the molecules or ions once and detect the intermediates and active species generated at that time. It was difficult to elucidate the mechanism of this and use it to identify intermediates. In addition, the rotating ring / disk electrode in the second method requires that the electrode be rotated at a relatively high speed during measurement, and cannot be measured in a solution system having a high viscosity or in a solid electrolyte. The rate at which active species generated at the disk electrode is detected on the ring electrode (capture rate) is at most about 40%. For intermediates with a short life, the number of revolutions of the electrode needs to be increased. There is a limit. Furthermore, since a considerably large amount of solution of about 100 ml is required for measurement, it has been difficult to apply it to measurement of a small amount of a solution such as a biological sample. In the case of the third method, most of the microelectrodes are made of metal wires, carbon fibers,
It is made by enclosing metal chloride etc.In this case, it is difficult to make the same electrode shape exactly, and the obtained electrochemical characteristics also differ depending on the electrode shape, such as a ring disk electrode In addition, it has not been possible to construct a measurement cell in which the shape of the electrode and the distance between the electrodes are important factors. In addition, only qualitative data can be obtained by measurement using ordinary three electrodes, and when quantitative data is required, it is necessary to test the electrodes beforehand, which requires a lot of measurement time. And Further, when it is not possible to carry out an assay for reasons such as contamination of electrodes by measurement, it has been very difficult to obtain quantitative data. further,
In order to construct an electrochemical element such as a cell for electrochemical measurement or a sensor using these fine electrodes, a reference electrode and a counter electrode are separately required in addition to the fine electrodes. Electrochemical reaction cannot be measured in the region, and the distance between the working electrode and the external reference electrode or counter electrode increases, so it is difficult to obtain a sharp response when measuring a high-resistance system such as a solid electrolyte. Disadvantages.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks, and the three electrodes of a comb-shaped electrode, a reference electrode, and a counter electrode are formed on the same reference, and excellent electrochemical performance is achieved without using external electrodes. An object of the present invention is to provide a microelectrode cell for electrochemical measurement capable of performing measurement and a method for manufacturing the same.

[Means for solving the problem]

In order to solve the above-mentioned drawbacks, the present invention provides a comb-shaped electrode and a reference electrode having a reference substance, which are alternately arranged in a comb shape from two opposing electrodes, and a counter electrode facing the reference electrode on the same substrate. Has formed.

Further, the three electrodes are formed on an insulating substrate by lithography technology, covered with an insulating film except for the three electrodes and the electrode pad, and the reference electrode is covered with the reference material. .

[Action]

Ions and molecules in the solution are measured by immersing the comb-shaped electrode, the reference electrode, and the counter electrode in the solution to be measured, and changing the potentials of the three electrodes.

〔Example〕

 Hereinafter, embodiments of the present invention will be described in detail.

Example 1 A photoresist (AZ-14 manufactured by Shipley Co., Ltd.) was placed on a silicon wafer having a 1 μm oxide film (manufactured by Osaka Titanium Co., Ltd.).
00-27) was applied to a thickness of 1 μm. The resist-coated silicon wafer was placed in an oven and baked at 80 ° C. for 30 minutes. Thereafter, contact exposure was performed for 20 seconds with a mask aligner (manufactured by Canon) using a chrome mask.
The exposed silicon wafer is 10% in monochlorobenzene.
After immersion for 20 minutes, development was carried out at 20 ° C. for 120 seconds in a resist developing solution (AZ Developer, Shipley), washed with water and dried to transfer the mask pattern to the resist.

The substrate with the resist pattern was mounted at a predetermined position in a spatter device (SPF332H, manufactured by Anelva), and chromium and platinum were sequentially sputter deposited. Sputtering was carried out under a pressure of 10 ^-2 Torr and an argon atmosphere for 10 seconds for chromium and for 1 minute for platinum, to a total thickness of 1000 A. Thereafter, the substrate was immersed in methyl ethyl ketone and subjected to ultrasonic treatment, and the resist except for the portion where the electrode was formed was removed to obtain an electrode pattern. After that, only the reference electrode of the substrate was connected to a lead wire and immersed in a silver plating heated to 60 ° C.
By applying a current of 1 mA for 10 seconds, silver plating was performed to deposit silver as a reference substance on the reference electrode.

After Mekko, spin on glass (OCD Type-
7) Using spin coating on the substrate, heat-setting at 450 ° C., applying a resist on the substrate again, baking at 80 ° C. for 30 minutes, and exposing using a mask , Developed, and covered with resist except for the comb electrode portion, the reference electrode tip portion, and the counter electrode.

The substrate after the patterning was subjected to reactive ion etching (using DM-451 manufactured by Anelva) using CF ₄ gas of spin-on glass using a resist as a mask to expose a comb-shaped electrode portion, a reference electrode tip portion, and a counter electrode. .

FIG. 1 is a plan view of the manufactured microelectrode cell for electrochemical measurement. In the figure, reference numerals 1a and 2a denote lead portions of comb-shaped electrodes arranged so as to face each other, reference numerals 1b and 2b denote electrode pads, reference numeral 3 denotes a reference electrode, reference numeral 4 denotes a counter electrode, and reference numerals 3b and 4b denote lead portions 3a and 4a, respectively. The connected electrode pads 5, 5 are insulating films, and 6 is a silicon substrate with an oxide film corresponding to the insulating substrate. FIG. 2 is an enlarged view of a portion A in FIG. In the drawing, reference numerals 1 and 2 denote comb-shaped electrodes which are arranged so as to mesh with each other so as to face the lead portions 1a and 2a facing each other. In the first embodiment, the electrode pitch was 5 μm, the gap was 2 μm, and the comb length was 2 mm.

The cell for microelectrochemical measurement was 1 mmol of ferrocene, 0.
Immerse in 1 mol of supporting electrolyte (tetraethylammonium perchlorate) in acetonitrile solution, connect each pad to bipotentiostat via lead wire, and connect one comb-shaped electrode from -0.3V to 0.5V for 100m.
When the potential was scanned at V / sec and the current was measured while the other was fixed at a potential of -0.3 V, the former showed a limit current indicating an oxidation reaction of ferrocene, and the latter a reduction current indicating a reduction reaction. From the magnitude of the current values of both, it was found that the capture ratio of oxidized ferrocene molecules at one comb-shaped electrode at the other comb-shaped electrode was 67%, which was higher than the value obtained with a normal rotating ring disk electrode.
A capture rate as high as 32% was obtained. Also, sample solution 1m
The measurement could be performed sufficiently at l or less, and the amount of solution could be reduced to 1/100 or less as compared with the ring disk method.

Also, 0.9 g of polyethylene oxide (manufactured by Aldrich, weight average molecular weight: 600,000) and 0.2 g of lithium trifluoromethanesulfonate are dissolved in 100 ml of a mixed solvent of 9: 1 acetonitrile and methanol, and 30 μl of the solution is placed on the microelectrode cell. The solvent was dried to obtain a polymer film. The electrode is then connected to a bipotentiostat and
When the potential of one comb-shaped electrode is scanned from -0.3 V to 0.5 V at 100 mV / sec and the other is fixed at a potential of -0.3 V and the current value is measured, the former performs the oxidation reaction of ferrocene and the latter performs the reduction reaction. The indicated limiting current was observed. From the magnitude of both current values, the capture rate of the oxidized ferrocene molecules at one comb-shaped electrode at the other comb-shaped electrode is 20%, which is a solid electrolyte that cannot be measured with the conventional ring-disk electrode. It has been found that the detection of the reaction intermediate therein is sufficiently possible.

Example 2 A photoresist (AZ-1400 manufactured by Shipley Co., Ltd.) was placed on a silicon wafer having a 1 μm oxide film (manufactured by Osaka Titanium Co., Ltd.).
-27) was applied to a thickness of 1 μm. The resist-coated silicon wafer was placed in an oven and baked at 80 ° C. for 30 minutes. Thereafter, contact exposure was performed for 20 seconds by a mask aligner (manufactured by Canon Inc.) using a chrome mask.
Exposed silicon wafer in monochlorobenzene
After immersion for 10 minutes, use a resist developer (Zipley, AZ
(Developer), developed at 20 ° C. for 120 seconds, washed with water and dried to transfer the mask pattern to the resist.

The substrate with the resist pattern was attached to a predetermined position in a vacuum deposition apparatus (manufactured by Nippon Vacuum), and chromium and gold were sequentially deposited by a resistance wire heating deposition method. Chromium is deposited for 5 seconds and gold for 3 minutes under a pressure of 10 ^-6 Torr, for a total of 1000
Deposition was performed to a film thickness of 20002000 A. Thereafter, the substrate was immersed in methyl ethyl ketone and subjected to ultrasonic treatment, and the resist except for the portion where the electrode was formed was removed to obtain an electrode pattern. Length of interdigitated comb-shaped electrode: 2 mm, pitch: 8
μm, gap: 5 μm. Thereafter, silver plating was performed only on the reference electrode portion under the same conditions as in Example 1, and silver as a reference substance was deposited on the reference electrode.

After Mekko, spin on glass (OCD Type-
7) using spin coating method on the substrate, heat curing at 450 ° C., and applying resist again on the substrate.
After baking at 80 ° C. for 30 minutes, it was exposed and developed using a mask, and covered with a resist except for a comb-shaped electrode portion, a reference electrode tip portion, and a counter electrode.

The substrate after the patterning was subjected to reactive ion etching (using DM-451 manufactured by Anelva) using CF ₄ gas of spin-on glass using a resist as a mask to expose a comb-shaped electrode portion, a reference electrode tip portion, and a counter electrode. .

The cell for microelectrochemical measurement was 1 mmol of ferrocene, 0.
Immerse in 1 mol of supporting electrolyte (tetraethylammonium perchlorate) in acetonitrile solution, connect each pad to bipotentiostat via lead wire, and connect one comb-shaped electrode from -0.3V to 0.5V for 100m.
When the potential was scanned at V / sec and the current was measured while the other was fixed at a potential of -0.3 V, the former showed a limit current indicating an oxidation reaction of ferrocene, and the latter a reduction current indicating a reduction reaction. From the magnitude of both current values, it was found that the capture rate of the oxidized ferrocene molecules at one comb-shaped electrode at the other comb-shaped electrode was 45%, which was higher than the value obtained with a normal rotating ring disk electrode.
A capture rate as high as 10% was obtained. Also, sample solution 1m
The measurement could be performed sufficiently at l or less, and the solution could be reduced to 1/100 or less as compared with the ring disk method.

Example 3 An electron beam resist (φ-MA) was formed on a quartz substrate having a thickness of 0.5 mm.
C, manufactured by Daikin Industries, Ltd.) to a thickness of 0.5 μm. The resist-coated quartz substrate was baked at 180 ° C. for 60 minutes in an oven. After that, it was put into an electron beam exposure system (JEOL: JSM-840), and the electron beam acceleration voltage: 5 KV, exposure amount: 5
Under the condition of μC / cm ² , only the interdigitated comb-shaped portions were exposed. After the electron beam exposure, the resist-patterned substrate developed and washed with the dedicated developer was sequentially sputtered with chromium and platinum in the same manner as in Example 1, and then the resist was peeled off. A photoresist (made by Shipley Co., Ltd.)
AZ-1400-27) is applied to a thickness of 1 μm, and the temperature is 80 ° C., 30 minutes,
After baking, the photomask is aligned and brought into close contact with the resist-coated substrate, and the patterns of the lead, the reference electrode, the counter electrode and the pad are exposed under the same conditions as in Example 2, and chlorobenzene treatment, development, cleaning, chromium, platinum The spatter deposit and the resist were stripped to form an electrode cell pattern.

The fabricated interdigitated electrode size is pitch: 35μ.
m, gap: 0.5 μm, comb length: 1.0 mm.

The substrate on which the electrode cell pattern was formed was fabricated in the same manner as in Example 1 by performing silver plating on the reference electrode, four electrodes, and spin-on-glass insulating films on portions other than the pad portion. I got

The cell for microelectrochemical measurement was 1 mmol of ferrocene, 0.
Immerse in 1 mol of supporting electrolyte (tetraethylammonium perchlorate) in acetonitrile solution, connect each pad to bipotentiostat via lead wire, and connect one comb-shaped electrode from -0.3V to 0.5V for 100m.
When the potential scan was performed at V / sec and the other was fixed at a potential of −0.3 V, and the current value was measured, the limit current indicating the oxidation reaction of ferrocene and the reduction reaction was observed in the former and the latter, respectively. From the magnitude of both current values, it was found that the capture ratio of the oxidized ferrocene molecule at one comb electrode at the other comb electrode was 80%, which was higher than the value obtained with a normal rotating ring disk electrode.
A capture rate as high as 45% was obtained. Also, sample solution 50
The measurement can be performed sufficiently at μm, and the amount of solution can be significantly reduced as compared with the ring disk method.

Examples 4 to 7 Comb mold length: 2 mm, pitch: 4 by the same method as in Example 1.
μm, gap: 1 μm (Example 4), 6 μm, gap: 3 μm
(Embodiment 5) Comb length: 1 mm, pitch: 7 μm, gap: 4 μm (embodiment 6), in the same manner as in embodiment 3, pitch:
1.5 μm, gap: 0.5 μm (Example 7)
An electrode cell for microelectrochemical measurement including two micro-comb electrodes was fabricated.

Table 1 shows the relationship between the supplementation ratio of ferrocene (the conditions were the same as in Example 2) and the size of the micro-comb electrodes, which were measured in the same manner as in Example 1 using these electrode cells, together with the results of Examples 1 to 3. Shown in

As described above, the relationship between the comb-shaped electrode pitch (gap) and the capture rate (measured with acetonitrile solution of standard substance: 1 mmol ferrocene, 0.1 mol tetraethylammonium perchlorate) was measured using a normal ring-and-disk electrode in each cell. An extremely large value is obtained from the obtained supplementation ratio.

In addition, the following materials including the materials shown in the above-described examples may be used as materials for manufacturing the microelectrode cell for electrochemical measurement according to the present invention. Examples of the substrate having an insulating surface or the whole include a silicon substrate provided with an oxide film, a quartz plate, an aluminum oxide substrate, a glass substrate, and a plastic substrate. Examples of the metal for the electrode include gold, platinum, silver, chromium, titanium, and stainless steel. Semiconductors for electrodes include p- and n-type silicon, p-type and n-type germanium, cadmium sulfide, titanium dioxide, zinc oxide, gallium phosphide, gallium arsenide, indium phosphide, cadmium selenium, cadmium tellurium, molybdenum disulfide, tungsten selenide , Copper dioxide, tin oxide, indium oxide, indium tin oxide and the like. The semimetal includes semiconductive carbon. As the reference substance on the reference electrode,
Silver, silver chloride, polyvinyl ferrocene and the like can be mentioned. Silicon oxide, silicon dioxide,
Examples thereof include silicon nitride, silicone resin, polyimide and its derivatives, epoxy resin, and thermosetting polymer.

Also, when fabricating microelectrodes, a resist is applied on the substrate, an image mask having a current pattern is overlaid thereon, or the pattern is directly exposed using an electron beam or the like and developed to develop the pattern on the substrate. After transfer to the resist above, metal, semiconductor, spatter, evaporation, CVD, coating method
Alternatively, a semi-metallic thin film is formed, and then the resist is peeled off to obtain a fine electrochemical cell consisting of four electrodes on the substrate, or a metal, semiconductor, or semi-metallic film on the substrate by sputtering, vapor deposition, CVD, or coating. After applying a resist on it, overlaying an image mask with an electrode pattern, or directly exposing the pattern using an electron beam, etc., developing and transferring the pattern to the resist, this is used as a mask An etching method for obtaining a fine electrochemical cell composed of four electrodes on a substrate by etching a base metal, semiconductor, or semimetal may be used.

Further, in order to manufacture a reference electrode, a metal serving as a reference substance and an organic redox polymer may be formed on one of two electrodes other than the comb electrode by plating and electrolytic polymerization.

〔The invention's effect〕

As described above, according to the present invention, since the three electrodes of the comb-shaped electrode, the reference electrode, and the counter electrode are formed on the same substrate, the measurement can be performed with high capture rate and high accuracy. Also, compared with the measurement using the conventional rotating ring / disk electrode, there is no need to rotate the external electrode or the electrode, so it has a very remarkable effect such as the measurement of a trace sample or the measurement of a biological sample. .

Further, since the electrodes on the insulating substrate are formed by using lithography technology, it is possible to obtain a stable electrode shape, to provide a degree of freedom in shape design, and to produce inexpensively and in large quantities.

[Brief description of the drawings]

FIG. 1 is a plan view of a microelectrode cell for electrochemical measurement showing an embodiment according to the present invention, FIG. 2 is an enlarged view of a symbol A in FIG. 1, and FIG. 3 is a conventional rotating ring disk. It is a principle diagram of an electrode. 1,2 ... comb-shaped electrode, 1a, 2a ... lead part, 1b, 2b ... electrode pad, 3 ... reference electrode, 4 ... counter electrode, 3a, 4a ...
Lead part, 3b, 4b ... electrode pad, 5 ... insulating film, 6 ...
... a silicon substrate with an oxide film.

Claims (2)

(57) [Claims] 1. A microelectrode cell for electrochemical measurement for measuring ions and molecules contained in water, an organic solvent, and a living body, comprising a comb-shaped electrode alternately arranged in a comb shape from two opposing electrodes. A microelectrode cell for electrochemical measurement, wherein a reference electrode having a reference substance and a counter electrode facing the reference electrode are formed on the same substrate. 2. A lithography technique comprising: a comb-shaped electrode alternately arranged from two electrodes facing each other on an insulating substrate; a reference electrode having a reference substance; and a counter electrode facing the reference electrode. A method of manufacturing a microelectrode cell for electrochemical measurement, comprising covering the insulating layer with only the three electrodes and the electrode pad, and covering the reference electrode with the reference substance.