JPS5924245A - Preparation of ion sensor - Google Patents

Abstract

PURPOSE:To obtain an ion sensor having stable quality, by a method wherein an ion sensor substrate is coated with a volatile hydrophilic solvent solution containing a plurality of metal alkoxides corresponding to a desired ion responsive glass composition and each metal alkoxides are subjected to hydrolysis and subsequently subjected to heat treatment to form an ion responsive glass film. CONSTITUTION:10g mixed metal alkoxides containing Si(OC2H5)4, NaOCH3, Al(OC3H7)3 and B(OC2H5)3 respectively in a mole ratio of 49:22:19.5:9.5 is added to 10ml ethanol to be uniformly stirred and mixed to prepare a mixed metal alkoxides-containing solution which is, in turn, applied to the pH responsive surface 9 of a pH glass electrode cylinder 8 and hydrolyzed thereon to form a uniform gel like film on said pH responsive surface. In the next step, said gel like film is subjected to heat treatment to form a Na<+> ion responsive glass thin film 10 through dehydro-condensation. In the next step, an inner electrode 11 comprising Ag/AgCl is inserted into the electrode cylinder and a 140mM NaCl solution is injected thereinto as an internal liquid 12 to obtain a Na<+> ion selective glass electrode 13.

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing an ion sensor.

More specifically, the present invention relates to an expedited manufacturing method of an ion sensor having a thin ion-sensitive glass membrane of stable quality.

Conventionally, ion-sensitive glass membranes of ion-selective glass electrodes, as typified by pH electrodes, have been produced by melting various raw materials at high temperatures (usually 1400° C. or higher) and molding them into a certain shape. However, with this method, it is difficult to obtain a glass film with the intended composition because the composition tends to change due to evaporation of volatile components during high-temperature melting, and there are production difficulties due to the generation of bubbles in the glass. Furthermore, in molding,
There is a limit to the thickness of the glass film, and therefore the obtained glass electrode also has a large internal resistance, which is disadvantageous in terms of accurate electrochemical measurements.

On the other hand, recently, a field effect transistor type ion selective electrode (IS-FET) has been proposed. However, it has been difficult to apply an ion-sensitive glass membrane as a sensitive membrane to such an 15-FET. That is, in order to cover the gate of a field effect transistor (FET) with glass, it is necessary to make the internal resistance of the glass extremely low, and usually it must be in the form of a thin film (0.3 μm or less). For this purpose, it is necessary to use methods such as sputtering, but even if a thin film is obtained, its composition cannot be controlled.
) was obtained.

By mixing metal alkoxides corresponding to the glass composition exhibiting ion-sensitivity, uniformly hydrolyzing the mixture, and then heat-treating it, an ion-sensitive glass with a controlled composition can be obtained. The present invention was achieved by discovering the fact that a thin ion-sensitive glass film can be easily formed on an ion sensor substrate.

Thus, according to the invention, a volatile hydrophilic solvent solution containing a plurality of metal alkoxides corresponding to a desired ion-sensitive glass composition is applied to an ion sensor substrate, where each metal alkoxide is hydrolyzed. A method for manufacturing an ion sensor is provided, which further comprises performing a heat treatment to form an ion-sensitive glass film.

The metal alkoxides used in this invention include various inorganic oxides (Na20XSiO2, AI!2o3, B2O3
etc.), and specifically, lower alkoxide metals corresponding to NaOCH3, Ca(OC2H5)2, s i(
QC2ns) Al! (OC3H7)3,B(OC
2H5) 3 etc. are mentioned. In this invention, a plurality of the metal alkoxides mentioned above are used in combination. This combination is determined depending on the desired ion-sensitive glass composition. For example, when Na-sensitive glass is intended, Si,
A combination of Na, Al and B alkoxides is sufficient.1. If H-sensitive glass is intended, Sl % N
It is sufficient to combine a and Ca alkoxides, and the same applies to other combinations.

In this invention, the above-mentioned mixture of metal alkoxides is
First, it is applied as a solution to the ion sensor substrate and subjected to hydrolysis to form a uniform gel-like film. At this time, it is preferable to use a volatile hydrophilic solvent as the solvent. This solvent may contain some water, but if water is present in sufficient amount, metal alkoxides that are easily hydrolyzed, such as NaOCH3 and Al (OC3H7), are usually dissolved.
3 tends to rapidly gel, making it impossible to obtain a uniform gel-like film, which is undesirable. In addition, when dissolving in a solvent, it is desirable to heat the solution to about the melting point of the metal alkoxide having the highest melting point to make the solution as uniform as possible.

Examples of the volatile hydrophilic solvent include methanol and ethanol.

The metal alkoxides in the applied solution are gradually hydrolyzed by water absorbed through the solvent, and as the solvent evaporates, a uniform gel-like film is formed. By heating the gel-like membrane thus obtained, the hydrolyzate of the gel-like membrane undergoes dehydration condensation and becomes glassy, yielding the ion-sensitive glass membrane of the present invention. The heating temperature at this time is usually about 800 to 500°C, which is sufficient, and there is no need to use high temperatures as in conventional melting methods. As described above, in the method of the present invention, since the raw materials can be applied in the form of a solution, the thickness can be easily controlled, and furthermore, it is easy to form a thin film. Furthermore, since a high-temperature melting process as in the conventional method is not used, a glass film having an intended composition can be stably formed.

By the method of the present invention, an ion-selective glass electrode, a coachite wire type ion-selective electrode, an 15-FET
You can obtain ion sensors such as

When producing an ion-selective glass electrode, an electrode tube with a carrier, such as glass, whose tip can be coated with an ion-sensitive glass membrane is used as a base material, and the surface of this base material is coated with the above-mentioned coating. Usually, by coating the ion-sensitive surface of a prefabricated or commercially available glass electrode tube and providing an appropriate internal electrode or internal solution, desired ion selectivity such as Na ion selective electrode can be achieved. Electrodes can be easily obtained.Also, when producing a coachite wire type ion-selective electrode, as shown in Figure 1, a metal lead wire (1) such as gold or platinum is coated with amalgam or solid electrolyte (e.g. , halides and sulfides of transition metals), etc., and then coated with the ion-sensitive glass film (3) of the present invention. Also, l5-FE
When producing T, the previously obtained pH-sensitive l5-
It can be easily obtained by using an FET as a base material and coating the ion-sensitive glass thin film of the present invention on its sensitive side (gate). Of course, as shown in Figure 2, <FE
Insulating layer (4) made of SiO2 on the channel region of T
silicon nitride (513
The ion-sensitive glass thin film (3) of the present invention may be formed on the silicon nitride by using the element on which N4) tbl is formed as a base material. Note that (6) is the source part, (7
) is the drain part. The processing procedures for manufacturing such an FET and forming the insulating layer (4) and the Si3N4 layer (5) are described in, for example, "J, Appl, phys, 49.58
(1980) and Masayuki Matsuo et al.

As described above, according to the method of the present invention, an ion sensor of stable quality can be produced without requiring high-temperature heating unlike the conventional melting method.

Furthermore, since the raw materials are used as a solution, minute ion-selective electrodes such as coachite wire type electrodes can be easily obtained, and thin sensitive membranes can be formed. It became possible to fabricate a 15-FET.

This invention will be explained below with reference to Examples.

Example 1゜Si(OC2H5)4, NaOCH3, Al(OC3H
7) 3 and B(OC2II5)3 each in a molar ratio of 4
10 g of mixed metal alkoxide containing 9:22:19.5 = 9.5 was added to ethanol lOmf' and heated to 80 g in a hot bath.
The mixture was stirred and mixed at ℃ for about 8 hours to obtain a uniform mixed metal alkoxide solution. This solution was applied to the pH sensitive surface (9) of the pH glass electrode tube (8) prepared in advance, and the solution was heated for about 10 minutes at room temperature.
Leave it for a minute. As a result, the metal alkoxide is hydrolyzed by moisture in the air, and a uniform gel-like film is formed on the pI-1kJ reaction surface. Next, this gel-like film was heated in an electric furnace to about 500° C. in air for about 10 minutes. As a result, the gel-like film is dehydrated and condensed to form an Na+ ion-sensitive glass thin film (10). After this, insert the internal electrode (II) of Ag/AgC1 into the electrode tube and
By injecting 0 mM NaCl solution as the internal solution (12), a Na″-ion selective glass electrode (13) as shown in FIG. 8 was obtained.

The response to Na+ ions of this electrode (Ag
/ Saturation KC with AgC4 as internal pole! The results of measurements using a reference electrode with a solution as the internal liquid are shown in Figure @4. In this way, linearity was obtained in the Na+ ion concentration range of 10 to 10, and the slope was 52 mV/dec.

Example 2゜Si(OC2H5)4, Na0CII3 and Ca(OC
A solution was obtained in the same manner as in Example 1 by adding logs of mixed metal alkoxides existing in 2H5)2 at a molar ratio of 72:20:8, respectively, to 10 d of ethanol. This solution was applied to the Na+ ion-sensitive surface of the Na+ ion-selective electrode tube prepared in advance, and a gel-like film was formed in the same manner as in Example 1.
A pH-sensitive glass thin film was formed by heat treatment. Then, a pH glass electrode was obtained by inserting an internal electrode of Ag/AgC1 and injecting an IN KCI solution. The pH responsiveness of this electrode was determined to be 0.00% with Ag/AgC1 as the internal electrode. FIG. 5 shows the results of measurement using a reference electrode with I N NaNO3 as the internal liquid. The solid line in FIG. 5 indicates the Nernst slope, and it can be seen that the pH glass electrode of the present invention has a sensitivity that almost matches the theoretical value.

[Brief explanation of the drawing]

1 to 8 are schematic structural explanatory diagrams illustrating the ion sensor obtained by the present invention, and FIGS. 4 and 5 are graphs illustrating the characteristics of the ion sensor obtained by the present invention, respectively. It is. +l)...metal lead wire, (2)...electronically conductive or ionically conductive material layer, (
3)...Ion-sensitive glass film, (4)...Insulating layer, valence)...Silicon nitride, (6)...Source part, (7)--Drain part, (8)... pH glass electrode tube, (9)...pH sensitive surface, layer...Na+ ion sensitive glass #membrane, (11)
...Internal pole, (14...Internal liquid, 0
31...Na+ ion selective glass electrode. 11-

Claims (1)

[Claims] fl) A volatile hydrophilic solvent solution containing a plurality of metal alkoxides corresponding to the desired ion-sensitive glass composition is applied to an ion sensor substrate, where each metal alkoxide is hydrolyzed. 1. A method for producing an ion sensor, characterized by forming an ion-sensitive glass film by further heat treatment. (2) The manufacturing method according to claim 1, wherein the ion sensor is an ion-selective glass electrode. (3) The manufacturing method according to claim 1, wherein the ion sensor is a coachite wire type ion-selective electrode. (4) The manufacturing method according to claim 1, wherein the ion sensor is a field effect transistor type ion selective electrode.