JPH051423B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Industrial Application Field This invention relates to an ion sensor. More specifically, the present invention relates to an ion sensor having a non-uniform ion-sensitive membrane with excellent durability.

(b) Prior art Conventionally, membranes in which various ion-sensitive substances are dispersed and held in hydrophobic organic polymers such as polyvinyl chloride and polyacrylic acid esters have been used as ion-sensitive membranes for ion-selective electrodes. . As the ion-sensitive substance, ion exchangers such as organic phosphorus compounds and neutral carriers such as valinomycin, monensin, and crown ethers are used.

These ion-sensitive membranes are so-called heterogeneous membranes that hold an ion-sensitive substance using a hydrophobic organic polymer as a matrix, and are usually formed into a membrane by adding an appropriate plasticizer, etc., and are coated with O2 on an ion-selective electrode substrate. -It is used by attaching it with a ring, etc.

On the other hand, there has been a strong demand for smaller and more complex ion sensors such as ion-selective electrodes.
Ion-selective field-effect transistors (IS-FETs) have been proposed using semiconductor technology. Such an IS-FET is a so-called field effect transistor (FET) in which the gate electrode is removed and an ion-sensitive film is formed there. However, since this gate film consists of an inorganic solid film mainly composed of silicon, such as a SiO ₂ -based glass film or a SiN ₂ -based glass film, the ion-sensitive films that can be formed on it are also limited. It has been practically difficult to form and use a non-uniform sensitive film having a matrix of hydrophobic organic polymers. That is, the adhesiveness between the ion-sensitive membrane and the gate membrane is poor, and peeling occurs in a short period of time when the membrane is immersed in the water to be measured.

Therefore, there has been a need for a technique for closely adhering a non-uniform ion-sensitive membrane to an inorganic solid membrane.

This also applies to coated wire type ion selective electrodes. If close contact is possible, even in the case of a normal ion-selective electrode, there is no need to attach a heterogeneous membrane after forming it in advance, and it is advantageous because it can be formed directly on the glass membrane as a base material.

(c) Purpose This invention has been made in view of the above points, and an object of the present invention is to provide an ion sensor comprising a non-uniform ion-sensitive membrane firmly adhered to an inorganic solid membrane such as glass. One of the purposes is

(d) Structure According to the present invention, the sensitive part of the ion sensor comprises an inorganic solid film mainly composed of silicon and an ion sensitive substance formed thereon dispersed in a hydrophobic organic polymer. The hydrophobic organic polymer is supported by organic polymer chains grafted onto the surface of the inorganic solid membrane via silane coupling agent residues. An ion sensor is provided.

The specific material of the above inorganic solid film is as follows:
SiO _2- based polymer (glass), Si ₃ N ₄ -based polymer, Si
Examples include (OH) ₄ gels, which may be composite membranes or may contain impurities. For example, when an IS-FET is intended, the FET gate film itself, which is made of an SiO ₂ -based inorganic solid film or a SiO ₂ -based inorganic solid with a Si ₃ N ₄ layer on the surface, can be targeted as mentioned above. , when an ion-selective electrode is intended, for example, a PH ion-sensitive glass membrane (containing impurities) is used as the sensitive part of the PH ion-selective electrode.
( _SiO2 -based polymer) itself can be targeted.
Of course, the newly formed Si on these films
(OH) ₄ -based gel membranes can also be targeted.

The ion sensor of the present invention usually has a silane coupling agent bonded to the surface of an inorganic solid membrane constituting the sensitive part of the ion sensor substrate as described above, and is bonded to the silane coupling agent thereon and subjected to condensation polymerization. A mixture of one or more monomers, an ion-sensitive substance, a hydrophobic organic polymer, and optionally a plasticizer, or a diluted solution thereof in a solvent, is applied, and the monomer capable of condensation polymerization is polymerized. It can be produced by holding at a temperature (usually 10 to 100°C) to grow polymer chains in a graft form through condensation polymerization, and removing the solvent as necessary. The combination of a silane coupling agent and a monomer that can be bonded to it and undergo condensation polymerization is a lower alkyltri-lower alkoxysilane having an amino group such as 3-aminopropyltriethoxylane (silane coupling agent), glutaraldehyde and Combinations of condensation polymerization monomers of alkyl dialdehydes and alkyl diamines, such as a combination of 1,8-diaminooctane, are preferred. The organic polymer chain obtained in this combination can be expressed, for example, by the following formula () As shown, it consists of a condensation polymer bonded with Schiff bases (-CH=N-). Note that A represents a silane coupling agent residue, B represents a glutaraldehyde residue, and C represents a diaminooctane residue. These polymer chains may be in a form in which their main chains are chemically bonded to at least an inorganic solid membrane in the form of a graft, and they may be polymer chains having a three-dimensional structure in which the respective main chains are cross-linked. Good too. Polymer chains having such a three-dimensional structure can similarly be formed by adding tri- or higher-functional monomers, such as trialdehydes or triamines, to the di-functional monomers.

The silane coupling agent can be immobilized on an inorganic solid membrane according to a method known in the field of immobilized enzymes. After treatment to introduce hydroxyl groups, the silane coupling agent
This is carried out by bringing the product into contact with an approximately 10% acidic aqueous solution and maintaining it under heating conditions of 30 to 100°C for 3 to 15 hours, and then removing unreacted coupling agents by washing with water. The solvent is not limited to water, and organic solvents such as toluene may also be used. however,
In the case of a Si(OH) ₄ -based inorganic solid film, the above hydroxyl group introduction step is not necessary because it itself has many hydroxyl groups on its surface. Furthermore, when an Si(OH) ₄ -based inorganic solid film is used, the adhesion is greater than that of an ion-sensitive film. Therefore, it is preferable to use an Si(OH) ₄ -based inorganic solid film, and even when using SiO ₂ or Si ₃ N ₄ -based solid films, it is possible to form a Si(OH) ₄ -based solid film on the surface. It is preferable to form an ion-sensitive membrane as a composite membrane. Such a Si(OH) ₄ -based inorganic solid film is produced by applying an aqueous solvent solution (e.g., aqueous methanol or aqueous ethanol solution) of a lower alkoxysilane such as tetraethoxysilane to an acidic state, and leaving it in place. It can be easily formed by drying and gelling a hydrolyzed solution of lower alkoxysilane.

Note that various ion-sensitive substances, hydrophobic organic polymers, plasticizers, etc. known in the art can be used in combination depending on the intended target ions. For example, when a neutral carrier such as potassium ion-selective valinomycin or crown ether is used as the ion-sensitive substance, and polyvinyl chloride is used as the hydrophobic organic polymer, the former should be 0.5 to 20% by weight of the latter. An ion-sensitive membrane is prepared by using the same amount or five times the amount of plasticizer (e.g., dioctyl phthalate, O-nitrophenyl octyl ether, etc.) as polyvinyl chloride, and uniformly mixing these in an appropriate solvent (e.g., tetrahydrofuran). The above-mentioned monomer may be added to the base and subjected to coating treatment.

Further, the thickness of the ion-sensitive membrane to be formed is preferably in the range of several μm to 1 mm in the case of an ion-selective electrode, and preferably in the range of 100 Å to 50 μm in the case of IS-FET.

As schematically shown in FIG. 1, the ion-sensitive part formed in this way has an ion-sensitive substance 3 dispersed and held in a hydrophobic organic polymer 2 on an inorganic solid film 1 mainly composed of silicon. A large number of organic polymer chains 4 extending from the inorganic solid film 1 in a graft-like manner are formed in the hydrophobic organic polymer layer. Therefore, the hydrophobic organic polymer 2 is supported on the inorganic membrane surface 1 by the organic polymer chains 4 by an anchoring effect, and the entire ion-sensitive membrane 5 is firmly attached to the solid membrane surface. Become. Therefore, the durability of the film is significantly improved compared to a simple coating film that does not form organic polymer chains, and it is possible to form a film that can sufficiently withstand long-term immersion in water.

Such a sensitive part can be applied to the sensitive parts of various ion sensors, and specific examples thereof include Nos. 2 to 4.
As shown in the figure. Figure 2 shows SiO ₂ system or SiO ₂ −
FET gate film 1a made of Si ₃ N ₄ based inorganic solid film
An IS-FET on which a Si(OH) ₄ -based inorganic solid film 1' is formed, and the ion-sensitive film 5 is formed thereon.
FIG. 2 is a schematic diagram illustrating an ion sensor of the form. In the figure, 6 indicates a drain portion, and 7 indicates a source portion. In addition, FIG. 3 shows the inorganic solid film 1'
3 is a diagram illustrating an ion sensor in the form of an IS-FET in which the surface of the gate film 1a is treated to introduce hydroxyl groups instead of forming , and then an ion-sensitive film 5 is formed in the same manner. Further, FIG. 4 shows that Si(OH) ₄ is applied to the sensitive surface of the PH electrode consisting of the electrode outer cylinder 9, the SiO ₂ glass inner cylinder 1b, the epoxy adhesive 8, the internal electrode 10, the internal liquid 10a, and the shield wire 11. This figure shows an ion sensor in the form of an ion-selective electrode in which an inorganic solid membrane 1' is formed, and the ion-sensitive membrane 5 is formed thereon.

(E) Examples Example 1 On the SiO ₂ -based glass film constituting the sensitive part of the PH glass electrode (20 x 3 mmφ), tetraethoxysilane containing a cellulose viscosity modifier: water: ethanol: hydrochloric acid (volume ratio 25:8:25:5) The mixed solution was applied by dip method, and heated at room temperature for 30 minutes, then at 80°C.
By leaving it for 15 minutes, the tetraethoxysilane was hydrolyzed and a solid film consisting of Si(OH) ₄ gel was formed. This sensitive part was treated with a toluene solution (30wt%) of 3-aminopropyl ethoxysilane.
The sample was immersed in the liquid at 80°C for 5 hours. This treatment converts 3-aminopropyltriethoxysilane into Si
(OH) Reacts with the hydroxyl group of the ₄ -based solid membrane, forms an ether bond, and is bonded to the solid membrane.

The above-treated sensitive part was mixed in the following proportions: Polyvinyl chloride: 250 mg (hydrophobic organic polymer) Calcium ²⁺ -Ionophore ETH1001: 10 mg (calcium ion sensitive material, manufactured by FLUKA A/G) Glutaraldehyde: ( 50% aqueous solution) 0.1 m (monomer for polymerization) 1,8-diaminooctane: 250 mg (monomer for polymerization) NPOE: 750 mg (plasticizer, O-nitrophenyl octyl ether) Tetrahydrofuran: Dip and apply in 5 m of the mixed solution for 30 minutes. A calcium ion sensitive membrane was formed by leaving it for 15 hours at a temperature of .degree. Through this treatment, the terminal amino group of the fixed silane coupling agent and glutaraldehyde form a Schiff bond, and further condensation polymerization of 1,8-diaminooctane and glutaraldehyde occurs, resulting in a Schiff bond as shown in the previous formula (). A calcium ion-sensitive membrane was formed in which organic polymer chains mainly consisting of the following were grafted from a solid membrane into a hydrophobic organic polymer, and the calcium ion sensor of the present invention as shown in FIG. 4 was obtained.

This ion sensor was tested under the following conditions: Test solution: Calcium chloride aqueous solution, 17℃
(Calcium chloride is special grade reagent.
(Water used is distilled deionized water) Reference electrode: Internal electrode Ag/AgCl, internal liquid saturated
The results of measuring the responsiveness using a KCl aqueous solution are shown in FIG. In this way, the calcium ion activity is 10 ^-5 ~
Linearity was observed in the range of 10 ^-1 mol/, and its slope was 27.0 mV/dec, which was close to the theoretical value of 28.7 mV/dec.

The durability of the calcium ion sensor of the present invention was compared with a simple coating film. The compared calcium ion sensor was an ion-selective electrode type sensor prepared in the same manner except that the silane coupling agent treatment and the addition of a polymerization monomer were not performed.

As a result, it was found that in the ion sensor of the present invention, no peeling of the ion-sensitive membrane was observed even when the sensor was left immersed in water for more than one month, indicating that the membrane was tightly adhered to and integrated with the sensitive part. In contrast, ion-sensitive membranes that are simply coated membranes tend to peel off after being immersed in water for 2 to 3 days, or water infiltrates the surface of the membrane to which they are attached, resulting in a decrease in performance, making it difficult to use in practice. was confirmed.

Example 2 On the gate film of an FET using SiO ₂ as the gate film,
A solid film made of Si(OH) ₄ gel was formed by the same method as in Example 1, and then reacted with 3-aminopropyltriethoxysilane. The sensitive part that underwent this treatment was as follows: 250 mg of polyvinyl chloride (hydrophobic organic polymer), 10 mg of valinomycin (potassium ion sensitive substance), 0.1 m of glutaraldehyde (50% aqueous solution) (monomer for polymerization), 1,8-diaminooctane 250mg (polymerization monomer) NPOE 750mg (plasticizer, O-nitrophenyl octyl ether) THF 5m (tetrahydrofuran, solvent) Dip and apply in a mixed solution and leave at 30℃ for 15 hours to form a potassium ion-sensitive membrane. and a potassium ion sensor (K ⁺ −IS−
FET) was obtained.

This K ⁺ -IS-FET was measured with a test solution: potassium chloride aqueous solution, 17℃ (potassium chloride is a special grade reagent, water is distilled deionized water), reference electrode: internal electrode Ag/AgCl, internal solution saturated KCl aqueous solution. , potassium activity is 10 ^-5 ~
It has linearity in the range of 10 ^-1 mol/, and its slope is
It was 57.0mV (theoretical value 57.4mV).

The results of the comparison with the one coated with a simple K ⁺ sensitive film using PVC as a matrix are shown in Example 1.
It was the same.

(f) Effects As described above, the ion sensor of the present invention has excellent durability because the membrane is tightly adhered to the inorganic solid membrane, even though it has a non-uniform ion-sensitive membrane. , which can withstand long-term practical use. Therefore, the application of the non-uniform type ion-sensitive membrane is expanded, and in particular, it is possible to form a non-uniform type ion-sensitive membrane on the gate film of FET, and an ultra-small IS- This makes FET possible. Furthermore, it has the advantage that the ion-sensitive membrane itself can be formed by a simple method of coating onto a substrate (inorganic solid membrane) without any special molding or cutting.

[Brief explanation of the drawing]

FIG. 1 is a schematic structural explanatory diagram showing a sensitive part in the ion sensor of the present invention, FIGS. 2 to 4 are structural explanatory diagrams illustrating specific examples of the ion sensor of the present invention, and FIG. 3 is a graph illustrating the ion responsiveness of the ion sensor of the present invention. 1,1′...Inorganic solid film, 1a...Gate film, 1b
...Glass inner cylinder, 2...Hydrophobic organic polymer, 3...Ion sensitive material, 4...Organic polymer chain, 5...Ion sensitive membrane, 6...Drain part, 7...Source part, 8...
Epoxy adhesive, 9... Electrode outer cylinder, 10... Inner pole, 10a... Internal liquid, 11... Shield wire.

Claims (1)

[Scope of Claims] 1. The sensitive part of the ion sensor is an ion-sensitive membrane formed by an inorganic solid film mainly composed of silicon and an ion-sensitive substance formed thereon dispersed in a hydrophobic organic polymer. An ion sensor characterized in that the hydrophobic organic polymer is supported by organic polymer chains grafted onto the surface of an inorganic solid membrane via silane coupling agent residues. 2. The ion sensor according to claim 1, wherein the organic polymer chain is a condensed polymer chain of an alkyl dialdehyde and an alkyl diamine.