JPH03221857A - Microelectrode cell for electrochemical measurement - Google Patents

Abstract

PURPOSE:To make electrochemical measurement at a low cost with high reliability by integrating and forming a working electrode, a counter electrode, a reference electrode, and an operation amplifier for amplifying a working electrode current on the same substrate. CONSTITUTION:The microelectrode cell is formed by integrating the working electrode 4, counter electrode 5 and reference electrode 6 consisting of metals, semiconductors or semimetals, and the operation amplifier (b) for amplifying the working electrode current on the same substrate 15. A resist is applied on the substrate 15 and an image mask having the patterns of the electrodes is superposed thereon or the patterns are directly exposed by using an electron beam or the like and the resist is developed to transfer the patterns onto the resist on the substrate; thereafter, the thin film of the metal, semiconductor or semimetal is formed by a sputtering, vapor deposition or coating method, etc., and the resist is peeled, by which the microelectrochemical cell consisting of the three electrodes is formed on the substrate.

Description

Detailed Description of the Invention [Industrial Application Fields] The present invention relates to an electric field used for electrochemically performing qualitative or quantitative analysis of ions and molecules contained in water, organic solvents, living organisms, etc. This invention relates to microelectrode cells for chemical measurements.

[Prior Art and Problems to be Solved by the Invention] Microelectrodes are suitable for analyzing microscopic areas such as in vivo and microscopic solution samples, so they have been used in combination with various organic or inorganic materials. Attempts have been made to apply them to sensors, etc., but many of these microelectrodes were made by 11 people using metal wires such as gold or platinum, carbon fibers, metal chlorides, etc. in glass capillary tubes. It has disadvantages such as not being suitable for mass production and not being able to obtain arbitrary electrode shapes such as comb-shaped or element-shaped.

Furthermore, in recent years, the application of lithography technology has been proposed as a method for creating microelectrodes. In this method, a resist is applied to a substrate, an image mask with an electrode pattern is placed over it, exposed to light, developed, and a thin metal film is formed by vapor deposition.The resist is then peeled off to create microelectrodes on the substrate. After forming a metal thin film on an insulating substrate (2), a resist is applied, an image mask having an electrode pattern is placed over it, exposure and development are performed, and the exposed portions of the metal film are coated using the remaining resist (1) as a mask. An etching method is used to create an electrode pattern by etching. By using these methods, it is possible to fabricate a large number of microelectrodes with arbitrary shapes on a substrate with good reproducibility. Therefore, the microelectrode fabrication method can be applied to microelectrochemical transistors (e.g., Journal of Phys.
89, p. 5133, 1985), electrochemical measurements of low molecules or polymer complexes using comb-shaped platinum @ electrodes (e.g., Analytical
tical Chemistry, Volume 58, Page 601,
(described in 1986). however,
These microelectrodes require a reference electrode and a counter electrode in addition to the microelectrode in order to configure a transistor and an electrochemical measurement cell, and the cell itself cannot measure electrochemical reactions in a microscopic area. However, because the distance between the microelectrode and the reference electrode increases, it is difficult to obtain a sensitive response when measuring high-resistance systems such as solid electrolytes.

In order to overcome this drawback, electrode cells for electrochemical measurements have been devised in which a working electrode, a counter electrode, and a reference electrode having a desired shape and size are integrated using lithography technology (for example, analytical Chemi
stry, vol. 60, p. 2770, 1988, etc.)
.

On the other hand, when using these microelectrodes, the current is also reduced due to the small area of the working electrode, e.g.
When measuring a sample with a concentration of mmol/Ω using a microdisk of +, the current potential will be approximately a few nA, which increases the noise and significantly reduces the S/N ratio. was there. Furthermore, there is a problem in that signal delay occurs due to capacitance due to the wiring between the electrode and the potentiostat, which increases response time and makes high-speed measurement difficult.

An object of the present invention is to solve the problems of the above-mentioned prior art and to provide a microelectrode cell for electrochemical measurements that has excellent characteristics, is highly reliable, and is inexpensive.

[Means for Solving the Problems] The above object is to provide an electrical system in which a working electrode, a counter electrode, a reference electrode made of a metal, a semiconductor, or a semimetal, and an operational amplifier for amplifying the working electrode current are integrated on the same substrate. This can be achieved by using a chemical d11j microelectrode cell.

Here, examples of the substrate include a silicon substrate with an oxide film, a quartz substrate, an aluminum oxide substrate, a glass substrate, a plastic substrate, and the like, as substrates whose surfaces or entire surfaces are insulating. In addition, metals for electrodes include gold, platinum, silver, chromium, titanium, etc.; semiconductors for electrodes include p-type and n-type silicon;
type germanium, cadmium sulfide, titanium dioxide, zinc oxide, gallium phosphide, gallium arsenide, indium phosphide,
Cadmium selenium, cadmium telluride, molybdenum disulfide, tungsten selenide, copper dioxide, tin oxide, indium oxide, indium tin oxide, etc., and semimetals for electrodes include conductive carbon. In addition, reference materials on the reference electrode include silver, silver chloride, polyvinylferrocene, etc., and insulating films include silicon oxide, silicon nitride, silicone resin, polyimide and its derivatives, epoxy resin, and cured polymers. I can do it.

[Function] By producing the microelectrode for electrochemical measurement having the above configuration using lithography technology, it becomes possible to produce electrodes having the same shape, the same performance, and the same characteristics at low cost and in large quantities. Therefore, it becomes possible to use the electrodes without testing each individual electrode. In addition, a working electrode,
Because the in-column electrodes and reference electrodes are integrated on the substrate,
Electrochemical measurements can be made on the part made up of these three electrodes. Furthermore, since the working electrode and the operational amplifier for amplifying the working electrode current are integrated, the wiring between the working electrode and the operational amplifier is extremely short, so it is resistant to noise and has little signal delay due to capacitance.

Although there are no particular limitations on the shape and size of the electrodes, the distance between the electrodes, etc., in order to obtain a more sensitive response, it is desirable to keep the distance between the working electrode and the reference electrode as close as possible. Furthermore, when measuring an electrochemical reaction in a minute area, it is necessary to design a mask or the like so that a working electrode, a counter electrode, and a reference electrode are arranged within that area.

The method for creating microelectrodes is to apply a cyst onto a substrate, overlay an image mask with an electrode pattern, or directly expose the pattern using an electron beam, develop it, and apply the pattern to the resist on the substrate. After transferring, metals, semiconductors,
Alternatively, a lift-off method can be used to obtain a microelectrochemical cell consisting of three electrodes on a substrate by forming a thin film of a semimetal and then peeling off the resist, or by sputtering, vapor deposition, carbon dioxide, etc. on a substrate.
A thin film of metal, semiconductor, or metalloid is formed by VD, coating method, etc., a resist is applied on the thin film, an image mask having an electrode pattern is overlaid, or the pattern is directly exposed using an electron beam, etc., and developed. After the pattern is transferred to a resist, the underlying metal, semiconductor, or metalloid is etched using this pattern as a mask, thereby obtaining a microelectrochemical cell consisting of three electrodes on the substrate using an etching method.

In addition, as a method for forming an insulating film pattern when leaving the electrode and pad portions and covering them with an insulating film, a resist pattern is formed on the substrate, and silicon oxide or silicon nitride is formed by sputtering, vapor deposition, CVD, coating, etc. , a lift-off method in which a substrate is coated with silicone resin, polyimide and its derivatives, epoxy resin, polymer cured material, etc., and then the resist is peeled off, sputtering, vapor deposition,
The substrate is coated with silicon oxide, silicon nitride, silicone resin, polyimide and its derivatives, epoxy resin, cured polymer, etc. by CVD, coating method, etc.
Examples include an etching method in which a resist is applied to a surface to form a pattern, and then the insulating film is etched using this as a mask to obtain a pattern, and a method in which a pattern is formed with a resist and then the resist is hardened and used as is. I can do it.

Note that to create a reference electrode, a metal or organic redox polymer serving as a supporting material is formed on one electrode other than the internal working electrode of the electrochemical cell by plating, electrolytic polymerization, etc. It can be created by

[Example] Hereinafter, the structure of the microelectrode cell for electrochemical measurements of the present invention will be explained in detail with reference to Examples.

However, the present invention is not limited to the contents of these Examples.

Example 1 Electrochemical measurement consisting of a CMO3FET type operational amplifier, working electrode, counter electrode, and reference electrode integrated on a silicon substrate using resist work, ion doping, etching, thin film formation, and other lithography techniques. I created a cell for FIG. 1 is a circuit diagram showing its configuration, FIG. 2 is a sectional view showing an example of its schematic structure, and FIG. 3 is an enlarged plan view of the electrode portion. In the figure, (a) is an electrode section, (b) is an operational amplifier section, 1 is a silicon substrate (P-), 2 is a passivation film, 3 is an aluminum wiring, and 4 is a working electrode (P-).
t), 5 is a counter electrode (Pt), 6 is a reference electrode (Ag),
7 is 3101wA18 is 0 well, 9 is P well, 10
is polycide, 11 is n+ polycide, 12 is sin
, a trench, 13 an insulating film, 14 an electrode window, 15 a silicon substrate with an oxide film, 16 a working electrode wiring, 17 a counter electrode wiring, and 18 a reference electrode wiring.

Here, the operational amplifier consisted of three stages of amplifier circuits (each circuit consisting of 10 FETs) connected in series with a gain of 33 dB. Also, the size of the entire circuit is 300 x 4o
o, m, total characteristics are input impedance 10paΩ
, open loop gain 97 dB, bandwidth 0.1 Mt
It was lz. The microelectrode part has a diameter of 10I! A reference electrode and a counter electrode were arranged around a working electrode of m, and a reference electrode and a counter electrode were formed. In addition, the entire cell was covered with a passivation film made of silicon nitride, leaving only the external terminals such as the electrodes exposed.

The microelectrode cell for electrochemical measurement prepared as above was mixed with 10 llmol of ferrocene, /Q, supporting electrolyte (
TeI laethylammonium barchlorate) 10m
Each pad was immersed in an acetonitrile solution containing mol/Q, connected to a potentiostat via its own lead wire, and the working electrode was heated from 0.3 V to 0.7'lT for 10
When potential scanning was performed at 0 mV/sec, the response shown in FIG. 4 was obtained. Furthermore, when similar experiments were conducted using electrodes having the same shape, a result was obtained in which the limiting current was 50 pA for all electrodes. On the other hand, when a similar experiment was conducted using a cell with the same electrode configuration but no operational amplifier connected to a potentiostat, the noise was large and an accurate limiting current could not be obtained.

Example 2 In Example 1, the potential scanning speed was set to I MV/sec and the measurement was performed. As a result, in the case of an electrode cell equipped with an operation amplifier on the same substrate, a signal could be observed although there was a charging current, whereas in an electrode cell without an operation amplifier, a signal could be observed due to the capacitance between the electrode and the potentiostat. The time constant became long and it was not possible to follow potential scanning.

Example 3 Polyethylene oxide (manufactured by Tosoh, weight average molecular ff
1570,000) 0.1. g t h') full, t rom') nce) l/lithium phonate 0.02g
was dissolved in 10 ml of an acetonitrile/methanol (9:2) mixed solution, and the solution was poured over an electrode prepared in the same manner as in Example 1 in an amount of 11-ml to largely cover it, and the solvent was evaporated to form a polymer film. The electrode is then connected to a potentiometer and the potential of the working electrode is set at 0,7 V with respect to the reference electrode, with a voltage of 1 mm
When a drop of 1,011 drops of ace].nitrile solution in which ferrocene was dissolved was dropped onto a portion of the above polymer 1 cm away from the electrode, a current flowed through the working electrode after 1 minute, and ferrocene could be detected.

Example 4 Dopamine, 5-hydroxytryptophan, ascorbic acid, and uric acid were dissolved in phosphate buffered saline at pH 6 and 5, respectively, and electrochemical measurements were performed using the same electrodes as in Section 1. As a result, dopamine 0. ], 4. V,
Redox was observed at 0.27 V for 5-hydroxytryptophan, 0.02 V for ascorbic acid, and 0.3 V for uric acid.

[Effects of the Invention] As mentioned above, by using a microelectrode cell for electrochemical measurements as an electrode cell having the structure of the present invention, the problems of the prior art can be solved and excellent characteristics can be achieved. It was possible to provide a highly reliable and inexpensive microelectrode cell for electrochemical measurements.

In other words, in the case of small electrode cells, working electrodes, counter electrodes, and reference electrodes are integrated on the same substrate using lithography technology, so electrode cells with the same performance and characteristics can be produced at low cost and in large quantities. I was able to get it. In addition, since it is possible to configure the working electrode, counter electrode, and reference electrode in a desired size and shape, they can be grouped into a minute area, making it possible to measure a very small amount of sample and to measure that area. It became possible to measure the local electrochemical reactions of Furthermore, since the operational amplifier is directly connected to the working electrode, signal delays due to noise and wiring capacitance can be significantly reduced.

The following two things have extremely significant effects on electrochemical measurements.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the configuration of a microelectrode cell for electrochemical measurement of the present invention, and FIG. 2 is a sectional view showing an example of its schematic structure.
Fig. 3 is an enlarged schematic plan view of the electrode portion, and Fig. 4 is a diagram showing cyclic portametry performed using a small electrode cell. 2. Passivation film, 3.
... Aluminum wiring, 4... Working electrode, 5... Counter electrode, 6... Reference electrode, 7... SjO
, membrane, 8...n well, 9...p well,
10...Vivolicide, 11-n" polycide, 12.Si(:l, h wrench, 13...
・Insulating film, 14... m-pole window, 15... oxide film (=j silicon substrate, 16... wiring for working electrode,
17... Wiring for counter electrode, 18... Wiring for reference electrode

Claims (1)

[Claims] 1. A microelectrode cell for electrochemical measurement, characterized in that a working electrode, a counter electrode, a reference electrode made of a metal, a semiconductor, or a metalloid, and an operation amplifier for amplifying the working electrode current are formed integrally on the same substrate. .