JPH0441778B2 - - Google Patents

Description

[Detailed description of the invention]

(a) Industrial application field This invention relates to an anion sensor and its manufacturing method. More specifically, the present invention relates to an anion sensor capable of measuring the concentration of specific anions in various electrolytes and a method for manufacturing the same. (B) Prior Art Conventionally, electrochemical measurement methods have been used to analyze various dissolved components in general samples and biological samples, and various ion sensors sensitive to various ions are known. However, these ion sensors had various problems. In other words, if we talk about chlorine ion sensors, for example, conventional chlorine ion sensors use Ag/AgCl-based solid electrodes or solid electrodes made by mixing AgCl with a matrix such as silicone rubber to form a membrane electrode. Although there are chloride ion selective electrodes, these have the disadvantage of being heavily contaminated by organic matter in living organisms such as proteins. Another example is a chloride ion selective electrode using a liquid ion exchanger, but this is impractical because it is a liquid membrane. On the other hand, a chloride ion selective electrode using an ion exchange membrane as an ion sensitive material has improved characteristics and has improved the drawbacks of the above electrodes. However, these membranes are cut out or molded into thin films from ion exchange resin, and are made into an ion-selective electrode with an internal electrode as shown in Figure 9 (in the figure, 1 is the ion exchange membrane, 2 is the internal pole, and 3 is the internal electrode). Although it can be used by attaching it as a liquid junction solution, 4 is an electrode cylinder, and 5 is a lead wire), it is applicable to coated wire type ion sensors in which an ion-sensitive membrane is directly coated on a metal electrode. In addition, it was also difficult to form it on a solid surface such as glass, which is often used as a sensitive surface of an ion sensor substrate. In other words, in order to form an ion exchange membrane on such a solid surface, operations such as dissolving the ion exchange resin in a solvent and applying it are necessary, but in this case, sufficient adhesion cannot be obtained and durable ion It is difficult to form an exchange membrane, and it is also difficult to control the thickness of the membrane, making it impossible to obtain an ion sensor with stable characteristics. On the other hand, recently, PHIS-FETs have been used in which a PH-sensitive film made of ceramics such as tantalum oxide is coated on the gate of a field-effect transistor, but in order to provide ion sensitivity other than PH sensitivity, In this case, it is necessary to form a desired ion-sensitive film on the sensitive surface or the gate of the FET, and in this case, there are problems similar to those described above. (c) Purpose of the Invention This invention has been made in view of the above-mentioned problems, and uses a polymer membrane as an ion-sensitive membrane, which can be manufactured easily and with stable quality, and has excellent durability. The present invention aims to provide an anion sensor equipped with the following features. (d) Structure of the Invention According to the present invention, an ion-sensitive membrane is formed on an ion sensor substrate, and this ion-sensitive membrane has an inner layer made of a plasma-polymerized polymer layer of a hydrophobic organic compound, It basically consists of a surface layer consisting of an amino group-containing polymer layer formed on top of the organic amino compound by plasma polymerization, and the amino group polymer layer of this surface layer has an ammonium salt type polymer layer formed by converting the amino group. An anion sensor characterized by having a hydrophilic group introduced therein is provided. Furthermore, a suitable method for manufacturing the above-mentioned anion sensor is provided. The most distinctive feature of this invention is that the anion-sensitive membrane is composed of a substantially hydrophobic inner layer and a surface layer having an ammonium salt type ion exchange group, and furthermore, both of these layers are formed by plasma polymerization. The reason is that it is composed of a polymer layer made of The inner layer of the sensitive membrane of the present invention is formed by subjecting the ion sensor substrate to so-called plasma polymerization conditions under the vapor of a hydrophobic organic compound with an appropriate mask. Examples of the hydrophobic organic compound in this case include various organic compounds that do not have a hydrophilic group, such as vinyl aromatic compounds such as styrene and divinylbenzene, aromatic compounds such as benzene and toluene, Examples include unsaturated hydrocarbons such as ethylene and propylene, and two or more of these may be used. It can also have a multilayer structure. Among these, it is preferable to use styrene, which is easily plasma polymerized. Although the conditions for plasma polymerization are not particularly limited, it is usually preferable to employ glow discharge conditions of 0.1 to 100 KHz in an atmosphere of the hydrophobic organic compound of 0.1 to 2 torr. The thickness of the inner layer formed directly on the ion sensor substrate in this way is usually 0.01 to 10 μm. This thickness can be easily controlled by adjusting the time for the plasma polymerization. The plasma-polymerized polymer membrane that constitutes this inner layer has a high degree of crosslinking and strong adhesion to adherends such as ion sensor substrates, and it also has hydrophobic organic It is a substantially hydrophobic membrane made of a polymer of compounds. Therefore, the base layer of the anion-sensitive membrane in the anion sensor of the present invention is useful for improving the durability, response stability, etc. of the membrane. On the other hand, the surface layer of the anion-sensitive membrane of the present invention is usually formed on the inner layer by first subjecting the ion sensor substrate on which the inner layer has been formed to plasma polymerization conditions under the vapor of an organic amino compound. It is produced by forming an amino group-containing polymer membrane, and then converting the amino groups in the amino group-containing polymer membrane into ammonium salt type ion exchange groups by chemical treatment. Examples of organic amino compounds in this case include amines having at least one linear substituent such as diallylamine, diamylamine, diethylallylamine, N,N,N',N'-tetramethyl-1,6-hexanediamine, and aniline. , pyridine, phenethylamine, and other cyclic or aromatic amines; other examples include triethylamine, ethylenediamine, diethylenetriamine, triethylenetetramine, and the like. Two or more of these may be used in combination. Among these, the tertiary group having a linear substituent such as tetramethylhexanediamine, diethylallylamine, etc.
Preferably, a grade amine is used. Further, as the conditions for plasma polymerization, it is usually preferable to employ glow discharge conditions of 0.1 to 100 KHz in an atmosphere of an organic amino compound of 0.1 to 2 torr. Also, the thickness of the surface layer is 0.01
It is appropriate to set the thickness to 10 μm, and this can be controlled by adjusting the thickness of the amino group-containing polymer film by changing the plasma polymerization time. In addition, vapor of a hydrophobic organic compound that can be used for forming the inner layer may be mixed at the initial stage of plasma polymerization of the organic amino compound, and in this case, the inner layer side of the surface layer formed is a mixture of the organic amino compound and the hydrophobic organic compound. The amino group-containing polymer layer is made of a copolymer with a synthetic organic compound, and is one preferred embodiment. The polymer film formed on the inner layer by plasma polymerization of an organic amino compound is a highly cross-linked polymer film containing amino groups, and the hydrophobic polymer film of the inner layer also undergoes a glow discharge. They are chemically bonded and integrated by the generation of radicals, etc. Not all the amino groups of the organic amino compound of the monomer remain in the chains of the polymer membrane after plasma polymerization. In other words, under the above plasma polymerization conditions for organic amino compounds, random polymerization and crosslinking reactions between carbon chains (substituents) due to the generation of many radicals and ions are considered to be dominant. Reactions such as decomposition of groups are also thought to be occurring. In this regard, the present inventors have also obtained an interesting finding that the amount of amino groups present in the polymer membrane obtained by plasma polymerization of the organic amino compound is larger on the surface side and smaller on the inner surface side. Such a gradient in the amino group content is particularly noticeable when an organic amino compound having the above-mentioned linear substituent is used,
Therefore, the ammonium salt type ion exchange group to be converted is also introduced with a corresponding gradient, and it is believed that such a gradient works more positively in terms of durability and responsiveness. The chemical treatment of the amino groups in the amino group-containing polymer membrane is preferably carried out by keeping the amino groups in the vapor of alkyl halide. As the alkyl halide in this case, it is appropriate to use lower alkyl monohalides, specific examples of which include methyl chloride, ethyl chloride, methyl iodide, methyl bromide, and the like. Upon contact with such alkyl halide vapor, the amino groups present in the amino group-containing polymer membrane are alkylated to form ammonium salt-type ions such as quaternary ammonium salts, tertiary amine salts, and secondary amine salts. converted into an exchange group. This contact can be carried out under heating to promote the reaction, but the reaction may also be carried out at room temperature. Further, it is preferable that the halogenated alkyl vapor is adjusted to contact the sensor formed with the amino group-containing polymer film at a flow rate of about 1/min under normal pressure. The appropriate contact (holding) time also depends on the thickness of the surface layer, but is usually 30
~300 minutes is suitable. The counteranion in the ammonium salt type ion exchange group in the surface layer can be appropriately converted to a desired anion, thereby changing the selectivity to anions. For example, when the counter anion is a chloride ion, it has high selectivity to chloride ions and is suitable as a chloride ion-sensitive membrane, but if the counter anion is a bromide ion or an iodide ion, the It has improved selectivity for these anion-sensitive membranes, and can be used satisfactorily as these anion-sensitive membranes. Examples of the ion sensor substrate on which the above-mentioned anion-sensitive membrane is adhered include various substrates having a fixed surface of metal, glass, ceramics, etc. as an ion-sensitive surface. By using a metal electrode such as platinum or silver as an ion sensor base material and forming the anion-sensitive membrane of the present invention thereon, a coated wire type ion-selective electrode as shown in Fig. 2 can be obtained. In the middle, 7 indicates a metal electrode, 6 indicates an anion-sensitive membrane of the present invention, which is composed of an inner layer 6a and a surface layer 6b], and the above-mentioned anion-sensitive membrane is similarly placed on the gate surface of the FET from which the gate electrode has been removed. By forming , it is possible to obtain an ion-selective field effect transistor (IS-FET) for anions as shown in FIG. 3 [in the figure, 9
10 is _a drain portion, 11 is _{a source} portion, and 12 is a silicon substrate]. Of course, as shown in FIG.
An ion sensor base material having an inner electrode 2 on the sensitive surface can be used as a glass electrode type ion selective electrode.In addition, various base materials such as a flow-through type ion sensor base material can be used. can be applied. As described above, the anion sensor of the present invention integrates a plasma-polymerized polymer membrane (surface layer) into which ammonium salt type ion exchange groups are introduced on a substantially hydrophobic plasma-polymerized polymer membrane (inner layer). Since the membrane is equipped with an ion-sensitive membrane made of oxide, the capture and dissociation of anions through water molecules in the electrolyte (measured liquid) containing the intended anions is carried out only on the surface area. There is substantially no migration of moisture or ions near the interface between the ion sensor base material and the ion-sensitive membrane. Therefore, it has excellent durability. In addition, the ion exchange groups introduced into the surface layer are often at the highest concentration in the surface layer, and decrease towards the inside, allowing for smooth capture and desorption of anions, further improving responsiveness. It is what was done. (E) Example A 7 mm square silicon wafer 16 was used as part of the ion sensor substrate, and was placed in close contact with one of the glow discharge electrodes in a container of a plasma polymerization apparatus.
After making the inside of the container a vacuum of 0.05 torr or less, styrene monomer gas was introduced and the pressure was adjusted to about 1.25 torr. In this state, the frequency is 1KHz, the current is 70mA,
Glow discharge was performed for 100 seconds at a voltage of 500 V to obtain a silicon wafer 16 on which a thin film of plasma polymerized polystyrene was formed on one side. Next, N,
Place the shear injected with N,N',N'-tetramethyl-1,6-hexanediamine into the container,
While degassing, vaporize this amino compound and reduce the pressure.
Adjust to 1torr, in this state frequency 1KHz, current
70mA, voltage 500V for 30 seconds and frequency 10K
Glow discharge was performed at Hz, current of 70 mA, and voltage of 500 V for 60 seconds to further form a plasma polymerized thin film of the amino compound on the polystyrene thin film. The silicon wafer with the composite plasma-polymerized film thus obtained was placed in a reaction vessel as shown in FIG. A silicon wafer 16 having an anion-sensitive membrane 6 of the present invention as shown in FIG. 5 was obtained by sufficiently contacting the wafer with the anion-sensitive membrane 6 to alkylate the amino groups. A flow-through type anion electrode 19 as shown in FIG. 6 was constructed using the silicon wafer thus obtained, and its responsiveness to chlorine ions was evaluated. In the figure, 17 is a flow-through type reference electrode (Ag/AgCl electrode; potassium chloride internal solution).
Reference numeral 18 indicates a liquid to be measured (for example, serum, diluted plasma, etc.). The results are shown in FIG. In this way, the response to chlorine ions is determined by the chloride ion concentration (activity).
is excellent in the range of 10 ^-4 to ^{10 0} M, −53 mA/
Linearity of dec was obtained. Further, interference caused by main anions was as shown in Table 1.

[Table] The ion sensors obtained in this way are
Although it was used continuously for several days, no change in sensitivity, etc. was observed, and even after two months had passed, no change in sensitivity, etc. occurred. Example 2 Except for using diethylallylamine instead of N,N,N',N'-tetramethyl-1,6-hexanediamine and applying the following plasma polymerization conditions,
A flow-through type chlorine ion electrode was produced in the same manner as in Example 1. [Conditions] Plasma polymerization of Γ styrene; 1.25 torr, 60 seconds,
50mA, 1KHz Plasma polymerization of Γ diethylallylamine; initial stage (styrene/diethylallylamine (1:1) copolymerization, 1.25torr, 60 seconds,
60mA, 1KHz) or later (diethylallylamine only, 0.6torr,
60 seconds, 60mA, 1KHz) Γ alkylation; treated with ethyl iodide for 3 hours The response of the chlorine ion electrode thus obtained to chlorine ions was linear in the range of 10 ^-4 to ^{10 -1} M (- 50mV/dec). Example 3 A flow-through type chlorine ion electrode was prepared according to Example 2, using the amino group-containing compound and plasma polymerization conditions set as shown below. [Conditions] Plasma polymerization of Γ styrene; 1.25 torr, 100 seconds,
50mA, 1KHz Plasma polymerization of Γphenethylamine; initial (styrene/phenethylamine (1:
1) Copolymerization, 1.4torr, 30 seconds, 60mA,
1KHz) or later (phenethylamine only, 1torr, 60 seconds,
80mA, 10KHz) Γ alkylation; treated with methyl chloride for 5.5 hours The response of the chlorine ion electrode thus obtained to chlorine ions was linear in the range of 10 ^-4 to ^{10 -1} M (-38 mV/dec) It was hot. Example 4 A flow-through type chlorine ion electrode was produced according to Example 2, using the amino group-containing compound and the plasma polymerization conditions as described below. [Conditions] Plasma polymerization of Γ styrene; 1 torr, 100 seconds,
60mA, 1KHz Plasma polymerization of Γ diallylamine Initial stage (styrene/diallylamine (1:1)
Copolymerization, 1.6torr, 30 seconds, 50mA, 1KHz) After (diallylamine only, 0.7torr, 60 seconds,
50mA, 1KHz) Γ alkylation; treated with methyl chloride for 4.5 hours The response to chloride ions of the chloride ion electrode thus obtained was linear (-35mV/dec) in the range of 10 ^-4 to 10゜M. It was hot. Reference Example A moisture-sensitive membrane with a double membrane structure formed in the same manner as in Example 1 except that methyl iodide was used as the alkyl halide, and N,N,N',N'-tetramethyl-
The content of ammonium groups in the surface layer of a moisture-sensitive membrane with a double membrane structure formed in the same manner as in Example 1 except that aniline was used instead of 1,6-hexanediamine and methyl iodide was used as the alkyl halide. The distribution of was measured using ESCA and Ar etching. The analysis conditions for ESCA are as follows. X-ray source: 9KV, 30mA, Mg target Scanning speed: 1eV/sec and 0.1eV/sec Ar etching: 2KV, 20mA Based on these measurement results, the relationship between film thickness and N ₁₃ peak intensity is shown in Figure 8. . In this way, compared to those using aromatic amines such as aniline as monomers for the surface layer,
When using an amine with a linear substituent such as tetramethylhexanediamine, the content of ammonium groups from the surface to the inside has a steep gradient, and the amount of ammonium groups on the surface is also extremely large. , was found to be more preferable in terms of rapid ion responsiveness. (F) Effects of the Invention As described above, the anion sensor of the present invention is provided with an anion-sensitive membrane that has excellent adhesion to the ion sensor substrate, and in which an ion exchange group is introduced into the surface layer of the sensitive membrane. Because of this, it has excellent durability and shows good responsiveness to anions.
Furthermore, the film thickness of the sensitive film can be easily controlled, and in particular, the film thickness can be controlled to be extremely thin, making it possible to obtain a film with low impedance, and a uniform and large-area sensitive film can be obtained regardless of the type of ion sensor substrate. It is advantageous in that it does not require skill to operate. Furthermore, since the production can always be carried out under dry conditions and commercially available gases can be used as they are, the production process is simple and economical with no loss.

[Brief explanation of drawings]

1 to 3 are configuration explanatory diagrams showing specific examples of the anion sensor of the present invention, FIG. 4 is an explanatory diagram showing one process of manufacturing the anion sensor of the present invention, and FIG. A perspective view showing a silicon wafer equipped with an anion-sensitive membrane in the invention,
FIG. 6 is a configuration explanatory diagram showing another specific example of the anion sensor of this invention, FIG. 7 is a graph illustrating the responsiveness of the anion sensor of this invention, and FIG. 8 is an anion-sensitive membrane in this invention. FIG. 9 is a graph showing the content distribution of nitrogen atoms in the surface layer in the thickness direction, and FIG. 9 is a configuration explanatory diagram illustrating a conventional ion sensor. 2... Internal pole, 3... Internal liquid junction solution, 4... Electrode tube,
6... Anion sensitive membrane, 6a... Internal layer, 6b... Surface layer, 7... Metal electrode, 9... Gate, 10... Drain part, 11... Source part, 12... Silicon base,
13...Glass film, 16...Silicon wafer.

Claims (1)

[Scope of Claims] 1. An ion-sensitive membrane formed on an ion sensor substrate, the ion-sensitive membrane comprising a hydrophobic and plasma-polymerizable vinyl aromatic hydrocarbon compound or an unsaturated aliphatic hydrocarbon compound. an inner layer consisting of a plasma-polymerized polymer layer formed with plasma-polymerized polymer layer, and diallylamine, diethylamine, diethylallylamine, N, N, N′, which can be plasma-polymerized thereon;
N'-tetramethyl-1,6-hexanediamine,
It basically consists of a surface layer consisting of an amino group-containing polymer layer formed by plasma polymerization of an organic amino compound selected from aniline, pyridine, phenethylamine, triethylamine, ethylenediamine, diethylenetriamine, and triethylenetetramine, and the amino group-containing surface layer An anion sensor characterized in that an ammonium salt-type hydrophilic group is introduced into the polymer layer by converting an amino group. 2. The anion sensor according to claim 1, wherein the amount of the ammonium salt type hydrophilic group introduced is inclined in the thickness direction so that it is larger on the surface side of the surface layer and smaller on the inner layer side. 3. The ion sensor substrate is subjected to plasma polymerization under the vapor of a hydrophobic and plasma-polymerizable vinyl aromatic hydrocarbon compound or an unsaturated aliphatic hydrocarbon compound to form a polymer film on its sensitive surface. ,
Next, plasma polymerizable diallylamine, diethylamine, diethylallylamine, N, N,
N',N'-tetramethyl-1,6-hexanediamine, aniline, pyridine, phenethylamine,
An amino group-containing polymer film is formed on the polymer film by plasma polymerization in the vapor of an organic amino compound selected from triethylamine, ethylenediamine, diethylenetriamine, and triethylenetetramine, and then in the vapor of an alkyl halide. A method for producing an anion sensor, characterized in that the amino groups in the amino group-containing polymer membrane are converted into ammonium salt-type hydrophilic groups by holding the amino groups in the amino group-containing polymer membrane. 4. The method of claim 3, wherein the alkyl halide is selected from the group of methyl chloride, ethyl chloride, methyl iodide, and methyl bromide. 5. A patent claim in which the plasma polymerization of hydrophobic and plasma-polymerizable vinyl aromatic hydrocarbon compounds or unsaturated aliphatic hydrocarbon compounds and organic amino compounds is carried out under high vacuum and under glow discharge conditions of 0.1 to 100 KHz. The manufacturing method described in Scope Item 3.