JPH085600A - Carbon electrode and its manufacture - Google Patents

Abstract

PURPOSE:To measure the concentration of an anionic chemical species easily and inexpensively by treating the carbon electrode part with a cationic surfactant. CONSTITUTION:Carbon electrodes 2, 3 (measuring electrode 2, counter electrode 3) with silver lead 5 are formed on an insulating board 1 and an insulating paste is printed on the carbon electrodes to form an insulating layer 6 which is subsequently removed partially to expose the electrodes 2, 3 acting effectively. It is then immersed into an aqueous solution of 1% cationic surfactant, e.g. hexadecyl trimethyl ammonium bromide for about 1min under normal temperature. Subsequently, it is cleaned with flowing water and dried at about 60 deg.C for 10min. Since this treatment eliminates anionic properties from the surface of the electrode 2, 3, the electron carrier can be measured accurately by applying a low voltage and the shelf life can be enhanced by protecting the electrode surface against contamination.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon electrode, particularly a carbon electrode used in various medical sensors or chemical analysis sensors, and a method for producing the same. Furthermore, the present invention relates to a biosensor using the above-mentioned carbon electrode and capable of quickly and simply measuring the concentration and the like of a specific component in various samples such as blood, and a method for producing the biosensor.

[0002]

2. Description of the Related Art A biosensor using an electrochemical detection means has been put into practical use as a method for quickly and simply measuring the concentration of a specific component in a sample such as blood. The present inventors have conventionally considered using a carbon electrode made of a carbon material in an amperometric sensor used in these biosensors.

Carbon materials are generally cheaper than noble metal materials, have a wide potential window, are chemically stable, and have other desirable properties as electrode materials. However, -COOH, -C = on the carbon electrode surface
Oxygen-containing functional groups such as O and —OH are present, and the surface of the carbon electrode becomes an anionic surface by the dissociation of these oxygen-containing functional groups in a neutral or alkaline solution. Therefore, Fe (CN) ₆ ^{3− / 4−} (that is, formula (I): Fe (CN) ₆ ³⁻ + e ⁻ ← → Fe (CN) ₆ ⁴⁻ )
The reaction of an anionic species such as
Due to both anionic properties, electrostatic repulsion occurs, the electrode reaction is suppressed, and the overvoltage increases. Therefore, in order to obtain a sufficient current value in the electrode reaction of anionic chemical species such as Fe (CN) ₆ ^{3− / 4−} on the carbon electrode, a large applied voltage is required.

In the measurement of anionic chemical species such as Fe (CN) ₆ ^{3- / 4-} (hereinafter simply referred to as Fe (CN) ₆ ^{3- / 4-} ) shown in the formula (I), a carbon electrode is used. And when measuring their concentrations by amperometry,
When an electrolyte having an electrolytic voltage value equal to or lower than the applied voltage coexists in the solution to be measured, the electrolytic current of the coexisting substance interferes with the measurement. In addition, an unstable residual current flows and S /
The N ratio (signal amount (S) / noise amount (N)) is deteriorated, and practically, there is a problem that the measurement accuracy is deteriorated in the measurement of the liquid to be measured containing various electrolytes. In addition, a portable sensor using a battery has another problem that power consumption is increased and battery life is shortened when a large applied voltage is required.

As a solution to such a problem, the following method has been proposed for the purpose of activating the carbon electrode. (1) As a polishing method using an abrasive, for example, by using diamond as an abrasive and polishing a glassy carbon electrode, the redox reaction rate of Fe (CN) ₆ ^{3- / 4-} at the electrode is increased (DCThomton Et al., Analytical Chemistry, Vol. 57, p. 150 (1985)). However, with this method, it is difficult to uniformly process many electrodes at once, the cost becomes high, and it is not suitable for mass production.

(2) As an electrochemical treatment method, for example, a voltage of 1.5 V is applied to a pyrolytic graphite electrode for 15
Fe at the electrode by electrochemical oxidation for minutes
(CN) ₆ ^3- reduction reaction rate increases. Further, by applying a voltage of 1.4 V to the pyrolytic graphite electrode and electrochemically oxidizing it for 20 minutes, the oxidation reaction rate of ascorbic acid at the electrode is increased. (RMWightman et al.
Journal of the Electrochemical Society, Vol. 131, p. 1578 (1984)). However,
This method is complicated in operation, high in cost, and unsuitable for mass production.

(3) As a heat treatment method, for example, a glassy carbon electrode is used under high vacuum of 2 × 10 ^-6 Torr or less 72
By heat treatment at a high temperature of 5 ° C, Fe at the electrode
(CN) ₆ ^{3- /} oxidation reaction rate of ⁴ redox reaction rate and ascorbic acid increases (DTFagan et al., Analytical Chemistry (Analytical Chemistry), Vol. 57, pp. 2759 (1985)). However, this method is complicated in operation, and in a system in which a carbon electrode is provided on an insulating substrate, it is necessary to use a heat-resistant insulating substrate, which results in high cost and is not suitable for mass production. Appropriate.

(4) As a chemical treatment method, for example, by modifying the surface of the carbon electrode with a polyamino acid using a condensation reagent and polyamino acid, the surface of the carbon electrode and Fe (CN) ₆ ^{3- / 4-} Electrostatic repulsion is resolved and fast electron transfer is observed (Taniguchi et al., 60th Conference of the Electrochemical Society, Proceedings, 242, 1993). However, this method is complicated in operation and uses an expensive polyamino acid, resulting in high cost and is not suitable for mass production.

Further, an example in which a surfactant layer is formed on an electrode is described in JP-A-4-212050. However, in this case, the purpose is to improve the wettability on the electrode, prevent the solution from being repelled on the electrode when the solution is spread on the electrode, and prevent peeling of the layer after drying. The purpose of the present invention is completely different from the purpose of accurately measuring the anionic species with a small applied voltage. Further, the electrode used is not limited to the carbon electrode, and the surfactant is not limited to the cationic surfactant. Examples of surfactants that can be used include nonionic surfactants and anionic surfactants.
Even if these nonionic surfactants or anionic surfactants are formed on the carbon electrode, the effects of the present invention as described below cannot be obtained. Therefore, Japanese Patent Laid-Open No. 4-2
The technique described in Japanese Patent No. 12050 is a technique completely different from the present invention.

[0010]

[Problems to be Solved by the Invention] Carbon electrode and Fe
In an electrode reaction with an anionic species such as (CN) ₆ ^{3- / 4-} , electrostatic repulsion occurs due to both anionic properties, the electrode reaction is suppressed, and the overvoltage increases, so it is sufficient. A large applied voltage is required to obtain a large current value. Therefore, using a carbon electrode, Fe (CN) ₆
^When measuring the concentration of anionic chemical species such as ^{3- / 4-} , as mentioned above, the measurement accuracy deteriorates due to the interference of the electrolytic current of the coexisting substance, and the power consumption is also large. There is a problem that

The above-mentioned treatment methods have been proposed as solutions to such problems, but any of these methods are complicated in operation and costly, and thus are not suitable for mass production. Therefore, the problem to be solved by the present invention is
It is an object of the present invention to provide a carbon electrode for use in an electrochemical sensor capable of measuring the concentration of anionic chemical species simply and inexpensively and with high accuracy, and a method for producing the same.

[0012]

Means for Solving the Problems As a result of intensive studies to solve such problems, the present inventors have treated the surface of a carbon electrode having a carbon material with a cationic surfactant. By an anionic species such as F
It has been found that the concentration of e (CN) ₆ ^{3- / 4-} can be measured easily, inexpensively and accurately. In the present invention, the anionic species means an atom or atomic group negatively charged in a solution, and examples thereof include hydroxysulfonic acid, anthraquinone-2,6-disulfonic acid, iron oxalate, ferrocene dicarboxylic acid, and hexacyanoruthenium. Examples thereof include acids.

Therefore, in the first aspect, the present invention provides
A carbon electrode having a carbon electrode portion formed of a carbon material on a base material, wherein at least a portion of the carbon electrode portion that effectively acts as an electrode (hereinafter, also referred to as an effective electrode portion) is a cationic surfactant. To provide a carbon electrode that has been treated by.

In a second aspect, the present invention is the method for producing a carbon electrode according to the first aspect, wherein at least the effective electrode portion of the carbon electrode portion of the carbon electrode is immersed in the cationic surfactant solution. Then, a method for producing a carbon electrode is provided, which comprises washing as required, or applying a cationic surfactant solution to at least the effective electrode portion and drying the solution. Therefore, the method of the present invention is extremely simple and can manufacture a carbon electrode at low cost.

In the present invention, the carbon electrode means an electrode using a material containing carbon as an electrode material. The carbon material used for the electrode portion of the carbon electrode is not particularly limited, as long as it has been conventionally used in the carbon electrode, for example, graphite, pyrolytic graphite, glassy carbon, carbon paste, Carbon fiber can be used.

Such a carbon material is arranged on a base material (for example, made of polyethylene terephthalate) as an electrode part, preferably as a layered electrode part, by a conventional method. Usually, an electrode part can be formed by screen-printing a carbon material in a paste form with a resin binder or the like and drying it. Further, a lead wire for connecting the electrode portion to the current measuring device, for example, a silver lead by screen printing is arranged so as to be in contact with the carbon electrode portion. Typically, after forming the carbon electrode portion, the electrode portion is formed by laminating an insulating material, for example, a layer of an insulating paste, for example, a layer of an insulating paste, in a state where only a portion acting as an electrode (that is, an effective electrode portion) is exposed. By doing so, they are arranged and insulated to complete the carbon electrode.

In the method for producing a carbon electrode of the present invention, the treatment with the cationic surfactant solution is performed after the insulating material is arranged, or after the carbon material and optionally the lead wire material are arranged. It may be carried out before placement, but since it is simple in the manufacturing process,
Particularly preferred is a method of treating after disposing the insulating material.

The structure of such a carbon electrode and the method for producing the same are well known, and are disclosed in, for example, JP-A-5-1647.
No. 24 can be referred to, and this can be referred to in the present specification. In the present invention, it is not always necessary to treat the entire surface of the electrode portion with the cationic surfactant, and it is sufficient to treat at least the portion that actually acts as the electrode.

In the present invention, the cationic surfactant which can be used means a surfactant which dissociates into ions and exhibits a cationic property when dissolved or dispersed, and examples thereof include an amine salt and a quaternary ammonium salt. Surfactants such as sulfonium salts and phosphonium salts, specifically hexadecyltrimethylammonium bromide, alkylamine salts, dialkylamine salts, tetraalkylammonium salts, trialkylbenzylammonium salts, alkylpyridinium salts, 2-alkyl-1-alkyl-
1-hydroxyethyl imidazolinium salt, N, N-dialkylmorpholinium salt, polyethylene polyamine fatty acid amide salt, salt of polyethylene polyamine fatty acid amide urea condensation product, polyethylene polyamine fatty acid amide urea condensation product quaternary ammonium salt, Amphoteric surfactant N, N-dimethyl-N-alkyl-N-carboxyalkylene ammonium betaine, N, N-dialkyl-aminoalkylenecarboxylic acid salt, N, N, N, which is an amphoteric surfactant which becomes a cationic surfactant in an acidic solution. -Trialkyl-N-sulfoalkylene ammonium betaine can be illustrated.

In the present invention, the treatment with the cationic surfactant may be any treatment for adhering the surface active groups of the cationic surfactant to the surface of the electrode portion of the carbon electrode. Specifically, a treatment of immersing the electrode portion in a solution of a cationic surfactant, a treatment of applying a solution of the cationic surfactant to the electrode portion, and the like can be exemplified.

The solvent for dissolving the cationic surfactant is not particularly limited, but a solvent which is usually water, methanol, ethanol, isolopropyl alcohol or acetone can be used, and particularly water and ethanol are preferably used. . Further, the concentration of the surfactant in the solution is not particularly limited and can be appropriately selected according to the surfactant used, but is usually 0.01 to 10 wt / v%, preferably 0.1.
It is sufficient to use a solution with a concentration of 1-2 wt / v%, for example 1 wt / v%. Further, the treatment temperature can be appropriately selected depending on the surfactant to be used, but it is usually sufficient to perform treatment at 5 to 50 ° C, preferably 10 to 30 ° C, for example 20 ° C. Usually, after treating with a solution, washing if necessary,
For example, it is washed with water and dried at an appropriate temperature depending on the cationic surfactant used, usually at 20 to 100 ° C., for example at room temperature. For example, in the case of treatment by immersion, it is generally preferable to wash after immersion. Also,
For example, in the case of treatment by coating, it is generally preferable that the coating is dried without being washed after coating.

In a third aspect, the present invention provides at least an enzyme and an electron carrier (mediator), such as potassium ferricyanide, on at least the effective electrode portion of the electrode portion of the carbon electrode according to the second aspect of the present invention. Provided is a biosensor having a solid-phased reaction layer comprising.

In the present invention, the reaction layer means a layer which enzymatically reacts with a component to be measured, and enables the oxidation current or reduction current resulting from the enzymatic reaction and the subsequent reaction with the electron carrier to be measured. Means a layer. The enzyme that can be used in the biosensor of the present invention is not particularly limited as long as it is generally used in biosensors, and it is an enzyme such as oxidoreductase, and specifically, glucose oxidase. , Alcohol oxidase, lactate oxidase, glucose dehydrogenase and the like.

The biosensor of the present invention is manufactured by a conventional method for manufacturing a biosensor having a carbon electrode, except that the effective electrode portion of the carbon electrode is treated with the cationic surfactant as described above. it can. For the conventional manufacturing method of this biosensor, see, for example, Japanese Patent Laid-Open No.
No. 164724, which can be referred to in the present specification. For example, the biosensor of the present invention is
The carbon electrode of the present invention obtained as described above is produced by applying a solution containing at least an enzyme and an electron carrier, for example, a phosphate buffer solution, on the working electrode part, and then drying. can do.

[0025]

The carbon electrode surface, which has become an anionic surface due to the dissociation of oxygen-containing functional groups such as -COOH, -C = O and -OH, is treated with a cationic surfactant to eliminate the anionic property of the carbon electrode surface. By this, Fe (C
N) The electrostatic repulsion between the anionic species such as ₆ ^{3- / 4-} and the carbon electrode is eliminated, and the overvoltage can be reduced. Therefore, the anionic species can be accurately measured with a small applied voltage. It becomes possible to do. Furthermore, Fe (CN) ₆
^In amperometric sensors and biosensors that use anionic species such as ^{3- / 4-} as electron carriers, the use of such cationic surfactant-treated electrodes makes it possible to accurately measure electron carriers with a small applied voltage. Since the measurement can be performed well, the measurement accuracy can be improved.

In the carbon electrode treated with the cationic surfactant by the above-mentioned method, the cationic surfactant is adsorbed on the carbon electrode, and the surface condition of the electrode is made uniform to obtain a carbon electrode having a constant performance. it can. Also,
For so-called dust components in the air, such as lint,
There are many substances that are positively charged, and there is a problem in that they are attracted and adsorbed by the anionic property of the carbon electrode surface, and the electrode surface is contaminated. However, by treating the active portion of the carbon electrode surface with a cationic surfactant, the anionic property of the carbon electrode surface disappears, and the phenomenon that the electrode surface is contaminated can be prevented, resulting in excellent storage stability. A carbon electrode can be obtained.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail with reference to the accompanying drawings with reference to the accompanying drawings. Example 1 (Production of Electrode) FIG. 1 shows an example of a view (plan view) of the electrode of the present invention seen from above. Carbon electrodes 2 (measurement electrode) and 3 (counter electrode) with silver lead wire 5 were formed on an insulating substrate 1 made of polyethylene terephthalate by a screen printing method (hatched portion). Next, an insulating paste was printed thereon to form an insulating layer 6 to expose only a predetermined working electrode portion. In the illustrated embodiment, the effective electrode portion is exposed within the circle 6. The obtained electrode was immersed in a 1% aqueous solution of hexadecyltrimethylammonium bromide, which is a cationic surfactant, at room temperature for 1 minute and then washed with running water at 60 ° C.
And dried in a dryer for 10 minutes to obtain a cationic surfactant-treated carbon electrode.

Example 2 (Measurement of Electrode Reaction) The effect of treating a carbon electrode with a cationic surfactant was F.
It was investigated by the electrode reaction of e (CN) ₆ ^{3- / 4-} . The cationic surfactant-treated carbon electrode prepared in Example 1 was treated with 0.1 M phosphate buffer (p of 5 mM potassium ferrocyanide and 5 mM potassium ferricyanide (p
H7.4) and measured cyclic voltammogram, and the result is shown by the curve (a) in FIG. The curve (b) in FIG. 2 shows the result of the same measurement performed using a carbon electrode that was not treated with a cationic surfactant. In the case of an untreated carbon electrode, the curve (b) has a large peak potential separation width (ΔE) and a small current value, whereas in the case of an electrode treated with a cationic surfactant, the curve (a) A waveform having a small separation width (ΔE) of the peak potential and a large current value was obtained. That is, it can be seen that a large current can be obtained with a small applied voltage.

Example 3 (Measurement of potassium ferrocyanide) Using the electrode prepared in Example 1, the concentration of potassium ferrocyanide was changed, a voltage of 100 mV was applied, and the current value after 5 seconds was measured. As shown in FIG. FIG.
(A) of FIG. 3 is a measurement result when a carbon electrode treated with a cationic surfactant is used, and (b) of FIG. 3 is a measurement result when a carbon electrode not treated with a cationic surfactant is used. As compared with FIG. 3B, the sensitivity of FIG. In addition, a carbon electrode not treated with a cationic surfactant was applied with a voltage of 300 mV, and the same measurement result was shown in FIG. 3 (c). It can be seen that, in the case of using the carbon electrode not treated with the cationic surfactant, the applied voltage of 3 times or more is required to obtain the same sensitivity as in FIG. 3 (a).

Example 4 (Measurement of Glucose) 50 on the carbon electrodes 2 and 3 prepared in Example 1.
A phosphate buffer solution having a pH of 7.4 containing mM potassium ferricyanide and 500 U / ml glucose oxidase (GOD) was added dropwise and dried to solidify potassium ferricyanide and the enzyme on the electrode. Next, a glucose solution was dropped as a sample solution on the electrode prepared as described above, and 25 seconds later, 10 seconds was applied to the measurement electrode 2 with the counter electrode 3 as a reference.
A voltage of 0 mV was applied and the current value after 5 seconds was measured, and the result is shown in FIG. In FIG. 4, (a) shows the measurement results when using a cationic surfactant-treated carbon electrode. Using glucose oxidase as a catalyst, glucose in the sample solution is oxidized and at the same time potassium ferricyanide is reduced to potassium ferrocyanide. And
By applying the above voltage, an oxidation current based on the concentration of potassium ferrocyanide is obtained, and it can be seen that this current value corresponds to the concentration of glucose as a substrate.

In FIG. 4, (b) shows the measurement results when a carbon electrode not treated with a cationic surfactant was used. In FIG. 4, the sensitivity in (a) was three times or more higher than that in (b). Further, the result of the same measurement by applying a voltage of 300 mV using a carbon electrode not treated with a cationic surfactant is shown by (c) in FIG. Therefore, when a carbon electrode not treated with a cationic surfactant is used, it is necessary to apply a voltage three times or more higher in order to obtain the same sensitivity as in FIG. Although hexadecyltrimethylammonium bromide was used as the cationic surfactant in the above examples, it is needless to say that other cationic surfactants exemplified above can be used in the above examples. You are not limited to ammonium bromide.

[0032]

According to the present invention, the surface of the carbon electrode is
By treating with a cationic surfactant, Fe (C
N) ₆ ^{3- / 4-} and the electrostatic repulsion between the anionic species and the carbon electrode disappears, and Fe (CN) is applied at a small applied voltage.
It becomes possible to measure anionic chemical species such as ₆ ^{3- / 4-} with high accuracy, and a carbon electrode having excellent storage stability can be simply mass-produced at low cost. Therefore, F
In an amperometric sensor or biosensor using an anionic species such as e (CN) ₆ ^{3- / 4-} as an electron carrier, by using such a cationic surfactant-treated electrode, high performance can be obtained. It becomes possible to mass-produce the sensor easily and inexpensively.

[Brief description of drawings]

FIG. 1 is a schematic plan view of a carbon electrode of the present invention.

FIG. 2 is a graph showing the results of cyclic voltammograms measured in Examples.

FIG. 3 is a graph showing the results of the potassium ferrocyanide response of the example.

FIG. 4 is a graph showing the results of glucose response of Examples.

[Explanation of symbols]

1 ... Substrate, 2 ... Carbon electrode (measurement electrode), 3 ... Carbon electrode (counter electrode), 4 ... Insulating layer, 5 ... Lead wire.

Claims (6)

[Claims] 1. A carbon electrode having a carbon electrode portion formed of a carbon material on a base material, wherein at least a portion of the carbon electrode portion which effectively acts as an electrode is treated with a cationic surfactant. A carbon electrode characterized by being present. 2. A carbon electrode is provided on an insulating substrate,
Next, a method for producing a carbon electrode, characterized in that at least a portion of this electrode that effectively acts as an electrode is treated with a cationic surfactant. 3. The production method according to claim 2, wherein at least a portion of the carbon electrode portion of the carbon electrode that effectively acts as an electrode is dipped in a cationic surfactant solution and then washed as necessary. . 4. The method according to claim 2, wherein a cationic surfactant solution is applied to at least a portion of the carbon electrode portion of the carbon electrode that effectively acts as an electrode, and the solution is dried. 5. A carbon electrode is provided on an insulating substrate,
The electrode is then treated with a cationic surfactant,
After that, a solution containing at least an enzyme and an electron carrier is applied onto the electrode and dried to form a reaction layer, which is a method for producing a biosensor. 6. The biosensor according to claim 1, wherein a reaction layer containing an enzyme and an electron carrier is formed on a portion that effectively acts as a treated electrode.