JPH0432985B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a gas sensor using an ion sensor (hereinafter referred to as ISFET) having an elongated gate insulated field effect transistor structure having a gate portion at one end and an electrode portion at the other end. be. (Prior art) It goes without saying that measuring the concentration of gases such as carbon dioxide and ammonia gas is important in industrial applications, but in recent years it has also become important to measure gas concentrations in living organisms in the fields of medicine and physiology. It is starting to be seen. For example, in physiology, the measurement of gas concentrations in a single cell provides important knowledge, and in medicine, continuous measurement of blood gas concentrations in anesthesia patients, critically ill patients, and patients in recovery rooms is essential in emergency situations. Helpful for discovery. For such purposes, extremely small gas sensors that can be inserted into cells or blood vessels are needed. Gas sensors using minute glass electrodes have been proposed for the above purpose. However, gas sensors used in the medical and physiological fields are inserted into a living body, for example, a blood vessel, so the diameter of the inserted part of the living body is 2 mm.
However, glass electrodes are difficult to handle because their size is limited and they are easily broken. In addition, since the electrode resistance of the glass membrane becomes large, it is necessary to separately install a high input resistance amplifier, and since the electrode resistance is also large, it is difficult to insulate and easily induces unnecessary noise.There are many problems that need to be solved in practice. It had In order to eliminate the drawbacks of conventional gas sensors using glass electrodes, the applicant has developed a gas sensor using ISFET that utilizes the field effect of semiconductors, which has been published in Japanese Patent Application Laid-open No. 56-2546 and Japanese Patent Application Laid-open No. 57-40641. proposed. In such a gas sensor, the gate part of an ISFET that is sensitive to ions is brought into contact with a gas absorption liquid whose ion concentration (for example, PH) changes as it absorbs gas, and the outside of the gas absorption liquid is covered with a gas permeable membrane. It can be manufactured by
The ISFET used in the above gas sensor has an insulated gate field effect transistor structure fabricated using IC technology, and a chemically selective film containing ion exchange substances, enzymes, etc. is formed at the gate of the transistor. It is an extremely small device that detects changes in the interfacial potential with the electrolyte on the surface of this chemoselective membrane and measures the concentration of specific ions in the electrolyte and specific substances that act on enzymes. The applicant of the present application has already proposed the specific structure of such an ion sensor in Japanese Patent Publication No. 43863/1983. A feature of such a known gas sensor is that the gate portion of the ion sensor having an insulated gate field effect transistor structure and the reference electrode are coated with a hydrophilic polymer containing a gas absorbing liquid. Its basic structure is shown in Figure 1. An ion sensor 1 having a gate insulated field effect transistor structure, a reference electrode 2, and a lead wire 4 connected to them at an electrode section 3 are embedded in a tube body 5 with an insulating resin 6. The gate part 7 of the ion sensor and a part of the reference electrode 2 are coated with a hydrophilic polymer solution 8 containing a gas absorbing liquid, and further covered with a gas permeable membrane 9. (Problems to be Solved by the Invention) However, it has been found that such known gas sensors have the following problems. (1) Since the characteristics of the gas sensor, especially the response speed, vary depending on the shape and thickness of the hydrophilic polymer layer 8, it is necessary to keep the shape and thickness of the hydrophilic polymer layer constant in order to produce a sensor with constant performance. However, it is extremely difficult to quantitatively coat the ISFET gate surface with a small amount of hydrophilic polymer in a uniform shape.
(2) Since the hydrophilic polymer 8 has fluidity, when the sensor receives external force during use, for example,
The shape shown in may be deformed as shown in FIG. 1b. Therefore, the characteristics of the sensor change during use. (3) Generally, the ion sensor 1 is thin and hard, whereas the gas permeable membrane 9 is often made of a fragile material such as thin silicone rubber.
When a gas sensor whose surface is covered with a fragile membrane is inserted into muscle tissue, the tip of the ion sensor breaks through the gas permeable membrane, exposing the gate as shown in Figure 1c, and the gas sensor may lose its function. (Means for Solving the Problems) In order to eliminate such drawbacks in conventional gas sensors, the applicant of the present application has conducted extensive research and has developed a solution of a hydrophilic polymer as a gas absorbing liquid holder, as in the past. The present invention was achieved by discovering that instead of using a porous hollow fiber formed in advance, it is sufficient to cover the entire tip of the ion sensor with the porous hollow fiber. Next, one embodiment of the gas sensor of the present invention will be described with reference to the drawings. FIG. 2 shows the basic configuration of the gas sensor of the present invention. In FIG. It is embedded in the insulating resin 6. The ion sensitive part (gate part) 7 of the ion sensor and a part of the reference electrode are inserted into the hollow part of one porous hollow fiber 8 and covered by this porous hollow fiber 8, and the porous hollow fiber and The gap between the hollow fiber and the ion sensor is filled with gas absorption liquid 9. The porous hollow fibers are further covered with a gas-permeable homogeneous membrane 10. In FIG. 2b, the reference electrode 2 is provided outside the porous hollow fiber 8, and the gas permeable membrane 10 is coated on the outside. Materials for the porous hollow fiber used in the gas sensor of the present invention include hydrophilic polymers such as polyvinyl alcohol and ethylene-vinyl alcohol copolymer, and hydrophobic polymers such as polyacrylonitrile, polyethylene, polypropylene, polysulfone, and polytetrofluoroethylene. Polymers are used. At first glance, hydrophobic polymers give the impression that they are unsuitable as carriers for gas-absorbing liquids (generally aqueous solutions); The gas-absorbing liquid can be easily retained by filling the tank with liquid and then replacing these organic solvents with water. These materials must be chemically stable. Since the gas absorption liquid is generally an alkaline or acidic solution, unless the material is chemically stable for a long period of time in such an atmosphere, the characteristics of the gas sensor will change over time. The inner diameter of the porous hollow fiber is preferably a size suitable for covering the ion sensor or the ion sensor and the reference electrode. The wall thickness of porous hollow fiber is 10
The thickness is preferably between 200 μm and 200 μm. If the wall thickness is thinner than this, spinning the hollow fiber becomes difficult and the mechanical strength also decreases, making it difficult to cover the ion sensor with the hollow fiber. When the wall thickness exceeds 200 μm, the response of the gas sensor becomes slow. Furthermore, since the outer diameter of the sensor as a whole becomes thicker, the degree of invasiveness becomes greater when indwelling the sensor in a living body. The porous hollow fibers are membranes used for ultrafiltration or precision filtration, and precision filtration membranes are usually used. Further, this film may have a skin layer or may be a homogeneous film. The porosity of the porous hollow fiber used in the present invention is 20 to 80.
% is preferred. Further, the pore diameter is preferably 0.03 μm to 5 μm. When the pore volume and pore diameter are smaller than the above ranges, the gas diffusion rate in the porous hollow fibers decreases, and the response of the gas sensor becomes slow. If the pore volume or pore diameter is larger than the above range, the mechanical strength of the hollow fiber will decrease, making it difficult to spin the hollow fiber itself or attach it to a sensor. It is necessary that the porous hollow fiber covers at least the gate part of the ion sensor, but in order to prevent the gas permeable membrane from being punctured by the ion sensor mentioned above, the tip of the ion sensor must be completely covered within the hollow fiber. It is desirable to cover it to the extent that it can be accommodated. As described above, the reference electrode may be housed inside the porous hollow fiber together with the ion sensor, or may be placed between the porous hollow fiber and the gas permeable membrane.
Generally, the former is preferable when the reference electrode is closer to the gate of the ISFET, since the induction nozzle is smaller. (Example) PH in which the entire circumference of the gate part is coated with silicon oxide and silicon nitride, described in Japanese Patent Publication No. 57-43863
Sensitive field effect transistor (length 5 mm, width
Ag-AgCl made by chlorinating silver wire (400μm)
A reference electrode was drawn into a nylon catheter (diameter 0.6 mm), and only the PH sensitive part of the transistor and the tip of the reference electrode were exposed and fixed to the width of the nylon catheter with silicone resin. On the other hand, porous hollow fibers of polysulfon were developed in JP-A-58.
-91822. That is, the porous hollow fibers are formed by extruding a spinning dope containing a pore-forming agent through an annular nozzle and then extracting and removing the pore-forming agent. Therefore, the shape of the porous hollow fiber is determined by the shape of the opening of the annular nozzle and the particle size of the fine powder of the pore-forming agent. The inner diameter of the hollow fiber is 325 μm, the outer diameter is 380 μm, and micropores with an average pore size of 1.2 μm exist on the outer surface with a porosity of 70%,
The inner surface had a microporous structure with many micropores of 0.1μ or more. The hollow fiber was placed over the exposed portions of the PH-sensitive field effect transistor and the reference electrode as shown in Figure 2a, and the hollow fiber was cut approximately 0.2 mm beyond the tip of the transistor. The hollow fiber part of this type of sensor is immersed in ethyl alcohol to allow the ethanol to penetrate into the pores of the hollow fiber, and then the hollow fiber part of the sensor is immersed in running water, and the ethyl alcohol in the pores is soaked. was replaced with water. After that, the hollow fiber part of the sensor was immersed in an aqueous solution containing 0.1M NaHCO ₃ and 0.05M NaCl, and NaHCO ₃ and NaCl were added into the pores.
spread. This was covered with a silicone rubber tube whose tip was sealed. In this way, Figure 2a
I made a carbon dioxide sensor like the one shown in . This carbon dioxide sensor was placed in the heart muscle tissue of a dog, and the partial pressure of carbon dioxide in the heart muscle during heartbeat was monitored for 2 hours. The sensitivity and response time of the sensor were measured before and after use in this animal experiment. Table 1 shows the results.
It was shown to. As is clear from Table 1, the sensitivity and response time of the carbon dioxide sensor made by this method hardly change even after being exposed to myocardial exercise.

[Table] Comparative Example A PH-sensitive field effect transistor and a reference electrode were embedded in a nylon catheter in the same manner as in the example and fixed with silicone resin. 0.1M
An aqueous solution containing NaHCO ₃ and 0.05 M NaCl and 10 wt% polyvinyl alcohol was added to the transistor.
A carbon dioxide gas sensor was made by coating the exposed parts of the PH sensitive part and reference electrode, and covering this with a silicone rubber tube with a sealed tip. Using this carbon dioxide sensor, the partial pressure of carbon dioxide in the myocardium of a dog was monitored in the same manner as in the example, and the sensitivity and response time before and after monitoring were measured. The results are shown in Table-2. As is clear from this, when a hydrophilic polymer solution is used as the gas absorption liquid, it is often damaged when the sensor is placed in the myocardium, and even if it is not damaged, the characteristics of the sensor change due to myocardial movement. The cause of all damage was the tip of the transistor puncturing the silicone rubber tube.

[Table] (Effects of the Invention) The gas sensor of the present invention has the following advantages over conventional gas sensors. (1) Porous hollow fibers are manufactured in advance using spinning technology, so
It is easy to keep the shape and pore distribution constant.
Therefore, variations in the characteristics of the gas sensor can be reduced. (2) Unlike polymer solutions, porous hollow fibers do not have fluidity and can maintain a fixed shape permanently, so the characteristics of the sensor are less likely to change due to external forces. (3) By covering the tip of the sensor with a porous hollow fiber, it is possible to prevent the gas permeable membrane from breaking at the tip of the sensor. As described above, the gas sensor of the present invention solves many of the problems of conventional gas sensors and is extremely useful in practice.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a conventional gas sensor.
FIG. 2 is an end view of the gas sensor of the present invention. 1...Ion-sensitive field effect transistor,
2... Reference electrode, 3... Electrode section, 4... Lead wire, 5... Tube body, 6... Insulating resin, 7... Gate section, 8... Hydrophilic polymer solution, 9... Gas permeation film.

Claims (1)

[Claims] 1. A comparison electrode is provided adjacent to the gate part of an ion sensor having an elongated gate insulated field effect transistor structure having a gate part at the tip and an electrode part at the other end, and the comparison electrode is provided adjacent to the gate part or the gate part and the comparison electrode. is inserted into the hollow part of a porous hollow fiber containing an absorption liquid whose ion concentration changes by absorbing gas, and covered with this porous hollow fiber, and the surface of the porous hollow fiber is covered with a gas permeable membrane. A gas sensor characterized by being coated.