JPS6015019B2 - Reference electrode consisting of a field effect transistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a comparison electrode made of a gate-insulated field effect transistor (hereinafter referred to as FET) and an ion measurement system equipped with the comparison electrode.

Ion sensor using FET was developed by King Berg in 1970.
Announcement of veld [lEEE Tra ship. Bio-Med
．． Eng. Vol. BME-17, 70 (1970)]
In 1978, King Matsuo and Esashi announced [EEET
Fake ns. Bio-Med. Eng. Vol. BME-2
5, 184 (1978)] and is recognized to have the following characteristics.

Since it is manufactured using IC manufacturing technology, it is easy to miniaturize and integrate. For example, several sensors can be made on a 0.5 side x 0.5 side silicon chip. (b) For the same reason, mass production is easy and therefore economically inexpensive.

C. By changing the gate sensitive membrane using the same method, it becomes possible to measure various ions.

D. Even if the sensor is miniaturized, the output impedance is low because the sensor itself functions as a multiplication element, and stable measurement is possible with a simple circuit.

In addition, the sensor can be easily packaged because the insulation between the electrodes and between the electrodes and the measurement circuit is not required to be as high as in ordinary microelectrodes. Because of these characteristics, FE
Ion sensors consisting of T are attracting attention as microsensors or composite sensors, and are expected to be used as sensors for medical purposes such as biological monitoring and blood analysis, for experiments in biochemistry and physiology, or as inexpensive disposable sensors. However, in order to perform measurements using such an ion sensor, a reference electrode that exhibits a constant potential difference regardless of the ion concentration of the sample solution is absolutely necessary, but the conventional liquid junction type reference electrode There is a limit to miniaturization, and as long as such a reference electrode is used, there is a limit to miniaturization of the FET ion sensor.

In order to solve this problem, the present inventors have already developed an FET in which the gate surface is coated with a hydrophobic organic polymer film.
Completion of a comparison electrode consisting of
No. 0093, Japanese Patent Publication No. 58-25221).

By using this reference electrode, it has become possible to obtain a very compact ion measurement system in which the FET ion sensor and the reference electrode are integrated. For example, it is possible to incorporate an ion sensor, a reference electrode, and the pseudo electrodes necessary to operate the measurement system on a single silicon chip, achieving ultra-miniaturization of the ion measurement system that was not possible with conventional technology. I was able to do that. However, in this reference electrode, since the hydrophobic membrane covering the gate surface is in direct contact with the test liquid, components such as proteins contained in the test liquid are likely to be adsorbed, which may cause the potential to fluctuate. was recognized.

For this reason, measurements in body fluids such as blood, fermentation culture fluids,
It has been found that there are practical problems in measurements in systems where proteins and various scales tend to adhere, such as industrial wastewater. Therefore, in order to overcome such drawbacks and obtain a reference electrode that is practically satisfactory and capable of stable measurements, the present inventors
As a result of intensive studies, it was discovered that it is effective to further coat the FET reference electrode coated with a hydrophobic membrane with a hydrous gel membrane, and the present invention was achieved. That is, the present invention provides an F material whose gate surface is coated with a hydrophobic organic polymer film.
A reference electrode made of ET, characterized in that a hydrous gel film is further provided on a hydrophobic organic polymer film, and the present invention also provides an ion measurement system using such a reference electrode. , (i) an ion sensor consisting of an FET that is sensitive to ions in the test liquid (ii)
) In an ion measurement system consisting of a pseudo electrode and (iii) a reference electrode consisting of an FET whose gate surface is coated with a hydrophobic organic polymer film, each component is coated with a hydrous gel film. This is an ion measurement system featuring:

The comparison electrode of the present invention consists of an FET element, a hydrophobic organic polymer film, and a hydrogel film.

The FET device used in the present invention is described in U.S. Pat.
This is a gate insulated FET described in No. 020,83, Samurai Kaisho 52-26,292, etc. Such FE
The gate insulating film of T is usually formed of silicon oxide or silicon nitride, but it is particularly preferable to have a two-layer structure in which a silicon nitride film is further formed on the silicon oxide film. It is advantageous for the insulation of the comparison electrode to be covered to the periphery. In the comparison electrode of the present invention, the gate insulating film of such an FET is coated with a hydrophobic organic polymer film. The hydrophobic organic polymer membrane in the present invention has an equilibrium water content of 0.5% by weight at 30°C.
The following are non-ion sensitive. A comparison electrode coated with such a hydrophobic film does not come into contact with the test liquid on the surface of the gate portion, so no interfacial potential is generated and it can be used as a comparison electrode. In the present invention, the materials forming the hydrophobic organic polymer film include olefins such as ethylene and propylene, woven materials such as tetrafluoroethylene, trifluoroethylene, hexafluoropropylene, monochlorotrifluoroethylene, and pnylidene nada. styrene monomers such as styrene, divinylbenzene, chlorostyrene, chloromethylstyrene, and methoxystyrene; halogenated olefins such as vinyl chloride, vinylidene chloride, chloroprene, and hexachlorobutadiene;
Polymers obtained by homopolymerization of monomers such as DEN, acrylonitrile, etc. or copolymerization using these monomers as main components are preferred. The method for forming a hydrophobic organic polymer film on a gate insulating film is as follows: (i) Dissolve a hydrophobic organic polymer in an appropriate solvent, apply the resulting solution to the gate surface, and then remove the solvent. Method of formation by evaporation.
Alternatively, (ii) a method in which a monomer solution containing a monomer or a partially polymerized product capable of producing a hydrophobic organic polymer is applied to the gate surface, and polymerization is performed by ultraviolet polymerization etc. to form a polymer film. can be mentioned. Among these, the latter method is preferred. Further, the thickness of the film formed on the gate insulating film is preferably 500A to lr. If it is thinner than this, pinholes are likely to occur in the membrane, and if it is thicker than this, the signal becomes unstable. In the present invention, a hydrous gel film is further provided on the hydrophobic organic polymer film.

In the present invention, "water content" refers to the membrane's equilibrium water content (3
0°C) is 20 to 2000% by weight (preferably 50 to 3
00% by weight). In addition, the equilibrium water rate is calculated as follows. Volume of water equivalent to waist 1 Equilibrium water content (wt%) = Weight of dry membrane x 100 If the equilibrium water content of the hydrous gel film is 2 wt% or less, (
i) Conductivity between the gate and the liquid becomes insufficient, making it easier to spread noise, (iii) interfacial potential between the gel and the liquid is more likely to occur, (iii) proteins, etc. are more likely to be adsorbed on the surface of the gel. This is not desirable because it causes

Conversely, membranes with high equilibrium water content tend to have low mechanical strength; however, if the reference electrode of the present invention is protected, such as by placing it in a cylinder, it can be used even with low mechanical strength. can. However, membranes having an equilibrium water content of 200% by weight or more are not preferred. There are no particular limitations on the material used for the hydrogel membrane. For example, {i} Inorganic hydrogels such as colloidal silica and ilminium hydroxide gel {0} Cellulose-based polypyrinyl alcohol, polyvinylpyrrolidone,
Water-soluble polymers such as polyacrylic acid, polymethacrylic acid, polyacrylamide, or polymethacrylamide made insoluble in water by copolymerization with divinyl monomers, or three-dimensionally crosslinked by light, radiation, etc. 9
Hydrous gel films can be obtained from various inorganic and organic materials such as copolymers whose main components are hydrophilic monomers such as acrylic acid, methacrylic acid, acrylamide, and methacrylamide.

In particular, the use of polymers containing hydrophilic acrylic esters or hydrophilic methacrylic esters as a material for the hydrogel membrane is advantageous in comparison with the present invention, since these polymers have excellent antithrombotic properties. This is very effective when using the electrode to measure ions in blood. The hydrophilic acrylic acid ester or hydrophilic methacrylic acid ester is preferably an ester of acrylic acid or methacrylic acid and a polyhydric alcohol having 2 or more hydroxyl groups and having 1 to 100 carbon atoms, such as ethylene glycol or propylene glycol. , butylene glycol, 1,4-dihydroxygothane, glycerin. diethylene glycol,
Examples include monoesters with triethylene glycol, polyethylene glycol, polypropylene glycol, etc. The hydrogel film in the present invention is formed from a polymer containing these monomers as constituent components, but the polymer is not only a homopolymer of these monomers, but also a monopolymer of these monomers. A copolymer manufactured to have the above-mentioned water content as a component may also be used.

As the copolymerization component, for example, hydrophobic monomers such as stinhle and methyl methacrylate, and hydrophilic monomers such as acrylic acid, methacrylic acid, acrylamide, and N-vinylpyrrolidone are used. In the copolymer, hydrophilic (
The proportion of hydrophilic monomers including meth)acrylic acid ester is usually 20 mol% or more, preferably 50 mol% or more. Among the copolymers mentioned above, the material for the hydrogel film in the present invention is a combination of a hydrophobic polymer containing styrene or methethyl methacrylate and a hydrophilic monomer such as hydroxyethyl methacrylate. A comb-shaped block copolymer obtained by polymerization is preferred. The above-mentioned hydrophobic polymer has a molecular weight of 50 and has a polymerizable double bond at the end.
0 or more, usually polystyrene or polymethyl methacrylate. The comb-shaped block copolymer has an AmBn skeleton (A , a hydrophobic monomer unit giving a hydrophilic polymer, B: a hydrophobic polymer unit having a polymerizable double bond at the end, m and n are arbitrary integers), Preferably, the content of hydroxyethyl methacrylate is 40 to 9
5% by weight. Such a comb-shaped copolymer itself is disclosed in Japanese Patent Application Laid-open No. 49-90743 and Tokusei No. 50-15079.
It is stated in No. 3, etc. By forming such a comb-shaped copolymer film on a hydrophobic organic polymer film, the present invention can prevent instability of measured values due to proteins contained in blood and also prevent blood formation. As a result, a stable reference electrode can be obtained. Furthermore, the comb-shaped plex copolymer film has increased strength compared to a homopolymer film of hydrophilic monomers due to the presence of the hydrophobic polymer portion, and is therefore superior in terms of durability. As a method for forming a hydrophobic gel film on a hydrophobic organic polymer film, the polymer forming the hydrophobic gel film is dissolved in non-water bath soot, and the hydrophobic organic polymer film is placed in the soot. A method of forming a film by immersing a coated FET electrode, pulling it up and drying it;
{o} For water-meltable polymers, create an aqueous solution of the polymer, add a small amount of crosslinking agent to it if necessary, immerse the electrode in the aqueous solution, pull it out, heat it, and irradiate it with light. A method of forming a membrane while performing a crosslinking treatment such as Examples include a method in which a monomer solution layer is formed on a polymer film, and the monomers are polymerized by heating or ultraviolet irradiation to form a hydrous gel film.

In many cases, hydrogel membranes and hydrophobic organic polymer membranes have poor adhesion, so the entire catheter is wrapped in hydrogel, or the sensor and reference electrode are placed inside the protective tube before being placed inside the protective tube. It is desirable to create a hydrous gel layer. The thickness of the hydrous gel film formed on the hydrophobic organic polymer film is preferably 10 to 3 thicknesses. If the thickness of the film is thinner than this range, the mechanical strength of the film will be weakened, making it easy to peel off or form pinholes, which is not preferable. Furthermore, if the film is thicker than this, it becomes easy to form bubbles due to drying, and if bubbles are formed, they swell again, making it difficult to maintain electrical contact. An ion measurement system can be constructed by using the comparison electrode made of FET obtained as described above and combining it with an ion sensor made of ET and a pseudo electrode that are sensitive to ions in the test liquid.

It has been found that in such an ion measurement system, it is preferable that the FET ion sensor and the pseudo electrode are also coated with a water-based gel membrane, similar to the reference electrode. An example of the circuit of the ion measurement system is shown in FIG. In Figure 1,
A is a comparison electrode made of the above-mentioned FET, and B is an ion sensor made of an FET, the gates of which are brought into contact with the measuring liquid. Furthermore, the pseudo electrode E for making the potential of the liquid constant is brought into electrical contact with the liquid, and the drain voltage of each FET A and B is made constant, and the constant current circuits C and C'
By applying a constant current to each of the electrodes and measuring the difference in source potential between the ion sensor and the reference electrode FET using an electrometer D, the concentration of the ion to be measured can be measured. Ion sensors consisting of FETs used in ion systems are disclosed in U.S. Patent No. 402,083;
Those described in Tokusekki No. 52-26292 and the like are used. Further, as the pseudo electrode, any material may be used as long as it is a good conductor, and since the potential with respect to the liquid does not need to be constant, a metal wire, metal foil, conductive paint, etc. can be used. Furthermore, in measurements in a living body, a skin electrode made of silver-silver chloride or the like may be used. As an ion measurement system, as shown in FIG. 2, it is possible to use a system in which many FET ion sensors (B to B3) are operated simultaneously by a comparison electrode A and a pseudo electrode E, which are each made of one FET. In the above ion measurement system, it is desirable that the FET ion sensor, the FET comparison electrode, and the pseudo electrode be integrated in many cases.

For example, it can be made on a single silicon chip. However, while it is preferable for the thickness of the hydrous gel film on the FET sensor to be thinner (less than 10 mm) due to its response time, the reference electrode should rather have a certain thickness (5 to 100 mm thick). ) is preferred from the viewpoint of mechanical strength and stability. Such an example is shown in FIG. In Figure 3, B is an ion-sensitive FET sensor, and A is an FET of the present invention.
This is a comparison electrode, and E is a pseudo electrode made of silver-silver chloride and serves as a support for the FET. These are bundled and put into a hollow body F, and covered with electrically insulating resin G except for the tip including the gate part. The gate portion is roughly covered with a hydrous gel film. At this time, the reference electrode FET can be protected from mechanical impact by thickly coating the reference electrode FET with a hydrous gel or covering it with a hollow body, as shown in the figure. Since the FET reference electrode of the present invention obtained as described above has a hydrous gel film on its surface, it is not affected by components such as proteins contained in the test solution, and provides accurate measurement values. was found to be stably obtained. In addition, the ion measurement system obtained by using such a reference electrode in combination with a FET ion sensor and a pseudo electrode each covered with a hydrous gel film is a type 4 system capable of accurate measurement, In particular, in an ion measurement system formed on the same silicon chip, the ion sensor and reference electrode are located very close to each other, so there is little noise due to biopotential or electromagnetic induction, and stable signals can always be obtained. Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 Tokubatsu Sho 54-66194 (Tokuiso Sho 52-1
After thoroughly cleaning the gate surface of the FET electrode (having a silicon nitride film on the gate surface) prepared according to the method described in 3267, CQ=C(CH3)CO
OC horse CH2CH2Si (OCH3) was immersed in a 25% hexane solution at 60°C for 30 minutes, further ultrasonically cleaned with hexane, and the gate surface was irradiated with a xenon lamp light source in P-chloromethylstyrene at room temperature vapor pressure. UV polymerization was carried out until a yellow interference color was obtained.

The FET reference electrode obtained in this manner is described in the above-mentioned Japanese Patent Application Laid-open No. The FETPR sensor and the pseudo electrode made of silver-silver chloride were incorporated into a nylon catheter with a diameter of 1.65 as shown in Figure 3. After insulating the bonding part with epoxy and silicone resin, the - Coating was performed by repeating immersion in a solution and drying. (Membrane thickness FET sensor; 5-1, reference electrode 100) In addition, the same polyhydroxyethyl methacrylate film was formed separately,
When the Heihei moisture content was measured, it was approximately 60%. After stabilizing the ion measurement system thus obtained by immersing it in water for one day, it was used to measure the walls of various solutions using a glass electrode (pH meter; M-7 type PH meter, glass electrode: #102). Ship-o5T Reference electrode: #201 Blood-05T
, both manufactured by Horiba, Ltd.).

As shown in FIG. 4, the values measured by the ion measurement system of the present invention even in solutions such as blood and surfactants showed good agreement with the values measured with the glass electrode. From this, it is clear that measurements by the ion measurement system incorporating the reference electrode of the present invention are accurate, and in addition to the fact that the system is extremely compact, Hiiragi will always find it useful. I was able to confirm that. Note that if the polyhydroxyethyl methacrylate film is not coated, as shown in Figure 4, accurate values cannot be obtained in blood, and the polyhydroxyethyl methacrylate film will be coated on the hydrophobic organic polymer film. It is clear that it is necessary to form a membrane. Example 2 In the same manner as in Example 1, a catheter as shown in FIG. 3 incorporating an FET sensor, a reference electrode, and a pseudo electrode was prepared.

5 between the reference electrode of this catheter and the inner wall of the catheter.
% agar aqueous solution and let it cool to gel. Furthermore, this catheter was coated with a composite electrode dip-coated with a 0.5% by weight dimethylformamide solution of a styrene/hydroxyethyl methacrylate comb block copolymer manufactured by the method shown below, and the catheter was coated with various pH values in the same manner as in Example 1. A good linear relationship was obtained when the solution was measured. In addition, this sensor can be inserted into a large amount of blood to determine the pH of the blood.
When measured, lower noise was obtained compared to when using a normal reference electrode. Almost no thrombus adhesion was observed after measurement. Styrene/hydroxyethyl methacrylate comb type.

The method for synthesizing the block copolymer is as follows. A monomer (molecular weight 14, 000) was dissolved in 120 g of dimethylformamide. To this, 152 hydroxyethyl methacrylate, 0.05 ml of ethylene glycol dimethacrylate and 0.2 ml of diisopropyl peroxydicarbonate were added and charged into a glass ampoule, and 3 unique polymerization was carried out at 60 qo. A copolymer containing 17.3% by weight of monomer components (equilibrium water content: 41.4%) was obtained.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of the ion measurement system used in the present invention, Fig. 2 is a circuit diagram of the combined ion measurement system, and Fig. 3 is a schematic diagram showing the ion measurement system of the present invention housed in a hollow space. It is. Moreover, FIG. 4 is a diagram showing the relationship between the values obtained by measuring the pH of various solutions with the ion measuring system of the present invention and the values obtained by measuring with a glass electrode. In FIGS. 1 to 3, Vo...drain voltage, V. V
,,V2,V3... Difference in source voltage, A...
...Reference electrode, B, B,, &, B3...Ion sensor, C,〇...Constant current circuit, D...Ammeter, E
...Pseudo electrode, F...Hollow body, G...
...Electrical insulating layer, day...Polyhydroxyethyl methacrylate gel In Figure 4, 1,1'...
Phosphate buffer, 2...StingSendr
oys buffer 17% albumin, 3...HEsting
Sendroys 11% HEPES (N-2-hydroxyethylpiverazine-N'-2-ethanesulfonic acid)
, 4, 4'... large ACD blood, 5... ratio sti
ngSendroys buffer + 0.5% fibrinogen, 6...HastingSeMroys+1% methylene flue, 7...HastingSeMroy
s10.5% sodium lauryl sulfate, 8,8'...H
astingSendro buffer, 9,9'...Human serum, 10,10'...Toji, 11,11'...
... Borax standard buffer, 0 ... Plot showing the relationship between the values measured by an ion measurement system incorporating a reference electrode coated with a polyhydroxyethyl methacrylate membrane and the values measured by a glass electrode. be. ●． This is a plot showing the same relationship as above when a reference electrode not covered with a polyhydroxyethyl methacrylate film is incorporated as the ion measurement system.
Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. In a reference electrode consisting of a field effect transistor whose gate surface is covered with a hydrophobic organic polymer film, a hydrogel film is further provided on the hydrophobic organic polymer film. Characteristic comparison electrode. 2. The comparative electrode according to claim 1, wherein the hydrous gel film is a hydrous gel film made of a polymer containing a hydrophilic acrylic ester or a hydrophilic methacrylic ester as a constituent component. 3. A comb-shaped block copolymer obtained by copolymerizing a hydrophilic acrylic ester or hydrophilic methacrylic ester as a constituent with a hydrophobic polymer containing styrene or methyl methacrylate as a constituent and hydroxyethyl methacrylate. The reference electrode according to claim 2, which is a composite electrode. 4 (i) Ion sensor consisting of an insulated gate field effect transistor that is sensitive to ions in the test liquid (ii)
In an ion measurement system consisting of a pseudo electrode and (iii) a reference electrode consisting of a field effect transistor whose gate surface is coated with a hydrophobic organic polymer film, each component is coated with a hydrophobic gel film. An ion measurement system characterized by: 5. The ion measurement system according to claim 4, wherein the hydrous gel film is a hydrous gel film made of a polymer containing a hydrophilic acrylic ester or a hydrophilic methacrylic ester as a constituent component. 6 A comb-shaped block copolymer obtained by copolymerizing a hydrophilic acrylic ester or hydrophilic methacrylic ester as a constituent with a hydrophobic polymer containing styrene or methyl methacrylate as a constituent and hydroxyethyl methacrylate. The ion measurement system according to claim 5, which is a polymer. 7. The ion measurement system according to claim 4, wherein the components (i), (ii), and (iii) are housed in the same hollow member. 8. The ion measuring system according to claim 4, wherein the thickness of the hydrous gel film covering the reference electrode is greater than the thickness of the hydrous gel film covering the ion sensor.