JPS62123349A - Microelectrode for electrochemical analysis - Google Patents

Abstract

PURPOSE:To obtain a microelectrode which is capable of electrochemically measuring material in a liquid stably and accurately, by constructing it of a carbon fiber and a non-conducting material as cover the fiber to partially scrape off one end of the carbon fiber. CONSTITUTION:The part 1 encircled by a dotted line is a carbon fiber and is covered with a non-conducting material 2. The part 3 is removed as shown by the alternate short and long dash line as one end of the carbon fiber, and hence it is hollow. The depth of the hollow part is normally up to about 500mum while the lower limit thereof about 0.5mum. A bundle of carbon fibers is preferably used. In this case, multiple carbon fibers are stuck with a non-conductive material such as epoxy resin. Viewed from the section, it is so arranged that individual carbon fibers exist as islands in a sea of the non-conductive material.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an improved microfabricated electrode for electrochemical oxidation-reduction measurements.

[Conventional technology]

BACKGROUND OF THE INVENTION Analytical methods are widely used in which a substance dissolved in a liquid is oxidized or reduced, and the amount of current generated during the oxidation or reduction is measured to quantify the substance to be measured.

For example, (1) when measuring dissolved enzymes in a living body or a fermenter, a method is used in which the dissolved enzyme is electrochemically reduced on an electrode and the amount of current generated is measured. (2) When measuring the oxidation-reduction potential of a substance dissolved in a solution, a method is used in which the substance is electrochemically oxidized and reduced, a voltage-current curve is obtained, and the oxidation-reduction potential is measured. .

Furthermore, (3) a so-called biosensor method is used in which a chemical substance to be measured is selectively reacted using an enzyme or a microorganism, and the generated compound is oxidized or reduced and the generated electric current is measured.

Microelectrodes for electrochemical analysis are used for multiple purposes as described above, so the relationship with conventional techniques will be explained for each case.

(1) The oxygen partial pressure of body fluids has a great effect on living organisms.

In recent years, with the advent of the C1ark type oxygen electrode, it has become possible to measure oxygen in vitro with high precision, and this has greatly improved the treatment of patients with respiratory disorders.

In addition, an intensive care unit (ICU) for cardiopulmonary resuscitation is also available.
The development of electronic care units also led to advances in oxygen partial pressure measurement.

In vitro measurements using such sample collection are limited by the frequency of sample collection, and changes may occur during sample storage, resulting in inaccurate measurements.

Therefore, it goes without saying that the ideal method is to continuously measure oxygen partial pressure by directly inserting an electrode into a living body.

A method of continuously measuring the oxygen partial pressure in a living body has also been proposed. In other words, using electrodes for metal production such as platinum, iridium, or gold and reference electrodes such as silver-silver chloride, a voltage is applied between these electrodes, oxygen is reduced at the working electrode (cathode), and the diffusion current is measured. This is an application of the principle of

At this time, if the oxygen concentration gradient at the surface of the electrode changes due to the movement of the myocardium or the pulsation of blood in the living body, the measured diffusion current will undergo a large change, making it impossible to accurately measure the oxygen partial pressure.

Various studies are being conducted to solve this problem. In other words, it is a miniaturized version of the so-called "Clark electrode," which separates both poles with an oxygen-permeable membrane and contains an electrolyte (see Bunji Hagiwara, "Oxygen Measurement by Electrode Method," Kodansha Scientific, 1977). ), a method in which the surface of a fine metal wire electrode is coated with a porous membrane consisting of a multilayer structure to create a stable contact state between the cathode surface and the solution (Japanese Patent Laid-Open No. 57
117838) or a method of inserting a thin wire metal electrode into a tube with an open end so that the tip of the electrode is set back from the open end of the tube (Japanese Patent Application Laid-open No. 195436/1983) has been proposed. has been done.

However, these methods require large electrodes and can only be inserted into specific areas, such as large blood vessels.
There were drawbacks such as the possibility of the porous membrane peeling off and causing iatrogenic diseases.

(2) It is one of the analytical methods that is often used to measure the oxidation/reduction potential of substances dissolved in a solution. That is, it is used for identifying substances, measuring ion concentration, etc. When using conventional electrodes, the current value is unstable when the solution is flowing, and measurement can only be performed when the solution is left still.

(3) In conventional biosensors, when installing a film containing enzymes or microorganisms on an electrode such as an enzyme electrode or a hydrogen peroxide electrode, it is necessary to strengthen the film, but this is difficult. There was also a drawback that it could not be made smaller. Various studies are being conducted to solve these problems. Specifically, in the case of glucose sensors, methods have been proposed in which a third component is added to the enzyme-containing acetylcellulose membrane to improve its strength, and methods are made in which the membrane is thickened or mechanically strengthened. . [Kaname Ito, Chemistry, Vol. 40, No. 6, 374-37
9 (1985)].

[Problem that the invention seeks to solve]

The present invention eliminates these drawbacks and provides electrodes for various sensors that electrochemically oxidize or reduce substances dissolved in a liquid continuously, stably, and accurately, and convert the resulting changes into electrical signals. It is something to do.

[Means for solving problems]

The above object is achieved by the present invention as described below.

In other words, the present invention focuses on carbon fiber (Tl) and a non-conductive material covering it! This is a microfabricated electrode for electrochemical analysis used in various sensors, characterized in that one end (3) of the carbon fiber is partially shaved.

The type of carbon fiber used is not particularly limited, and carbon fibers made from polyacrylonitrile, pitch, rayon, phenol resin, etc. or carbon fibers produced by vapor phase growth are preferred.

The diameter of the carbon fiber is usually 30 μm or less, particularly preferably 20 μm or less.

As the non-conductive substance, there are no particular restrictions, but polymeric materials such as fluororesin, polyester resin, epoxy resin, polyphenylene oxide resin, polyphenylene sulfide resin, urethane resin, silicone resin, and phenol resin are used, and antithrombotic substances are used. It is preferable to use a superior resin.

It is also possible to use ceramics.

The structure of the sensor of the present invention is exemplarily shown in FIG.

The part surrounded by the dotted line in (1) in the figure is carbon fiber, and (
2) is a non-conductive material covering it. One end of the carbon fiber, the part (3) indicated by the dashed line, has been removed, so this part is hollow.

The depth of this hollow portion is usually up to 500 μm, and it is generally undesirable to make it deeper. Its lower limit is 0.
It is about 5 μm.

It is particularly desirable to use a plurality of bundles of carbon fibers. In that case, multiple carbon fibers are hardened with a non-conductive material such as epoxy resin, so that when looking at the cross section, each carbon fiber exists as an island component in a sea of non-conductive material. Configure.

In the sensor of the present invention, for example, carbon fibers are first covered with a non-conductive substance by a dipping method or the like, and the resulting composite material is cut to form an electrode surface layer, but the cross section is usually polished before use.

A commonly used method is used for cross-sectional polishing. The cross-sectional shape is not particularly limited, and may be a flat, spherical, or pointed shape depending on the purpose of use. The electrolytic oxidation method is preferable for the process of cutting down one end of the carbon fiber, but
The method is not limited to any method as long as only carbon fibers are decomposed and removed. The electrolytic oxidation method will be explained in more detail below. As the electrolytic solution, an acidic or alkaline aqueous solution, an aqueous solution containing dissolved salts, and an alcohol such as methanol are used. The carbon fiber is connected to the anode, and anodic oxidation is performed using a metal electrode as the counter electrode. The voltage during oxidation is preferably in the range of 1 to 100 volts.

Another preferred method is a method in which oxidation and reduction are repeated.

If the amount removed by decomposition is small, the amount of oxidation current or reduction current is likely to change depending on the flow of the liquid, while if the amount removed by decomposition is too large, the amount of oxidation/reduction current tends to become too small.

When used as an electrode for a biosensor, there is no need to use a membrane containing enzymes or microorganisms as in conventional biosensors, and the enzymes or microorganisms may be immobilized by some method in the partially carved portion. Also in this case, if the amount of decomposition and removal is too small, immobilization will be difficult, and if it is too large, the amount of current will be small.

The depth of the carved part varies depending on the purpose, but is usually 0.5 to 500I! m, special D2-2o.

μm is preferred.

Although the carbon fiber surface may be used as it is as an electrode portion having oxidation/reduction ability, one preferable method is to modify the carbon fiber by modifying its reactive surface.

When using a material with oxygen reduction catalytic activity such as platinum, iridium, gold, zinc, phthalocyanine, or Prussian blue as a modification material, use a conventional method such as vacuum evaporation, sputtering, plating, or ion implantation electrolytic oxidation polymerization method. is used. Modification with a functional substance is also one of the preferred methods.

At this time, the surfaces of the carbon fibers may be completely covered with these materials, but they may also be partially made to resist adhesion or injected.

If visitor substances are present during measurement, it is preferable to apply a thin film on the electrode surface by a conventional method to exclude these substances and allow only the necessary substances to pass through.

The electrode of the present invention is preferably minute when used for direct insertion into a living body, but does not necessarily have to be minute when used for use in a fermenter or the like.

〔Effect of the invention〕

The microfabricated electrode of the present invention is substantially unaffected by flow and can stably and accurately electrochemically measure substances in a liquid.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Examples 1, 2.3 and Comparative Example (1) A bundle of 1,000 carbon fibers (Trading Card T-3001K, diameter 7 μm) was soaked in an epoxy resin containing a hardening agent to impregnate it with the resin. Next, this impregnated fiber bundle was heated and cured while being stretched to obtain a wire-like composite material with a diameter of about 0.8 mm. The sides of this were completely insulated with epoxy resin, then cut, and the cross section was polished using a conventional method.

The polished portion was immersed in a 2 mmol sulfuric acid aqueous solution, and anodic oxidation was performed using a platinum wire as a counter electrode under the conditions described below. Using the obtained sensor, we investigated the effect of liquid flow on the current caused by enzyme reduction. That is, physiological saline is poured into a flask equipped with a magnetic cooler, the above-mentioned sensor is attached as an operating rod, and a silver/silver chloride electrode is attached as a counter electrode.
The enzyme was saturated by exposure to air at room temperature.

A negative voltage of 0.75 volts was applied to the actuating rod, and the flowing reduction current was measured. The current flowing when the magnetic cooler was rotated as fast as possible and when it was left standing was measured and the ratio was calculated.

Example 1 was oxidized at 1.75 volts for 15 minutes and continued.
The operation of energizing 1 or 2 volts was repeated 35 times. In Example 2, oxidation was carried out by passing a current of 1 microampere for 80 minutes, and then reduction was carried out in physiological saline at -0.7 volts for 10 minutes.

In Example 3, electrolytic oxidation was performed for 9 minutes at 0.5 milliamps, and then reduction was performed for 10 minutes at 7 volts in physiological saline.

As a comparative example, measured values using an electrode before oxidative etching treatment are shown.

The results are shown in the table below.

Example 4 and Comparative Example 2 The electrode obtained in Example 3 (Example 4) and the electrode before oxidative etching (Comparative Example 2) were treated with 0.01 M Ka Fe (CN)b and 2 wt% NaCl, respectively. The cyclic portangram was measured using the three-electrode method using an aqueous solution containing .

The results are shown in FIG. 2A (Comparative Example 2) and B (Example 4).

When a is stationary, b is when stirring by N2 bubbling is performed.

It can be seen from the figure that Comparative Example 2 is greatly affected by the flow of the liquid, but Example 4 is hardly affected by the flow.

[Brief explanation of drawings]

FIG. 1 shows the configuration of the sensor of the present invention, and FIG. 2 shows a cyclic portamography.

Claims (1)

[Claims] (1) Carbon fiber (1) and non-conductive material covering it (2)
A microelectrode for electrochemical analysis, characterized in that one end (3) of the carbon fiber is partially shaved.