JPH04223B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a Severinghaus type gas sensor using a hydrogen ion sensitive FET converter having an elongated gate insulated field effect transistor structure having a gate portion at one end and an electrode portion at the other end. 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, measuring gas concentrations in living organisms has begun to be viewed as important in the medical field. For example, in medicine, continuous measurement of blood gas concentrations in anesthesia patients, critically ill patients, and patients in recovery rooms helps detect emergencies. Such a purpose requires an extremely small gas sensor with a diameter of 2 mm or less that can be inserted into blood vessels or muscle tissue. Conventionally, a Severinghaus type gas sensor using a minute glass electrode has been used for the above purpose. However, it is known that the following problems occur when glass electrodes are downsized. (a) Since the resistance value of the glass membrane is approximately 10MΩ, an amplifier with a high input resistance value is required. (b) Glass membranes are thin and have low mechanical strength. (c) The resistance value of the glass film increases because the electrode area becomes smaller. As a result, the measuring device becomes large and complicated, and the electrode itself is fragile and easily damaged, which poses practical problems, especially as a sensor that is inserted into living tissue to measure the gas concentration in the living body. On the other hand, a carbon dioxide sensor using a metal oxide solid PH electrode instead of a glass electrode is disclosed in Japanese Patent Application Laid-Open No. 17495/1983. This sensor is smaller and thinner than a gas sensor using a glass electrode, making it suitable for use as a sensor inserted into living tissue; however, (a) the sensor is inflexible because it uses a solid electrode; . (b) Electrical resistance increases due to miniaturization. It has drawbacks such as: Therefore, there was a limit to miniaturization. These problems can be solved by using a hydrogen ion sensitive FET converter (hereinafter referred to as PH-ISFET) having a gate insulated field effect transistor structure described in Japanese Patent Publication No. 57-43863 instead of glass electrodes and solid electrodes. He was released. Such PH−
Gas sensors using ISFET are PH-ISFET and PH-
A reference electrode is deposited on the substrate near the gate of the ISFET, a lead wire is connected to the PH-ISFET and the reference electrode, and an insulating tube houses the PH-ISFET and the reference electrode. - Electrical insulation where the gate of the ISFET is positioned in the opening provided in the insulating tube, the lead wire is extended along the tube, and the tube is filled between the inner wall of the tube and the lead wire connection part to close the tube. A hydrophilic polymer layer containing a resin and an electrolyte whose hydrogen ion concentration changes by absorbing gas, which is coated so as to span both the gate part of the PH-ISFET and the reference electrode, and at least the entirety of the polymer layer. This is a gas sensor composed of a gas permeable membrane. The above gas sensor is suitable for use as a gas sensor inserted into a living body. However, PH
-ISFET usually has a photosensitivity of about 10 ^-5 to ^{10 -6} V/Lux in absolute value, and when using a gas sensor using PH-ISFET for monitoring during surgery, etc.
During surgery, the light sensitivity of the PH-ISFET is a major obstacle in practical use, as it receives illumination of several thousand to tens of thousands of lux from a surgical light. In order to eliminate the photosensitivity of PH-ISFET, PH-
JP-A-53-146693 describes coating the gate portion of an ISFET with a hydrophilic polymer colored black. However, the above proposal is for negotiating the photosensitivity of ion sensors using ISFETs, and is not related to gas sensors. PH-ISFET used in gas sensors has a black-colored hydrophilic polymer coated on the gate.
In principle, it is possible to eliminate the photosensitivity of gas sensors by using ISFETs. In that case, the gate part of the PH-ISFET and the reference electrode are coated with a gas-absorbing liquid-containing hydrophilic polymer colored black, and the outside thereof is coated with a permeable membrane. However, it has become clear that there are the following problems in reducing the photosensitivity of a gas sensor using this method. (1) Photosensitivity of PH-ISFET exists not only in the gate part but also in the entire Si substrate including the electrode part. Therefore, even if only the gate portion is coated with a black polymer as described above, it is difficult to completely eliminate photosensitivity. (2) Severinghaus type gas sensors measure gas concentration using minute PH changes in gas absorption liquid. Therefore, it is necessary to prevent the pH of the gas absorption liquid from changing due to factors other than the gas concentration. However, many black pigments are chemically unstable and become acidic during long-term storage, for example due to air oxidation, which often leads to changes in the characteristics of the pigment as a gas sensor.
Therefore, a gas sensor using a PH-ISFET whose gate portion is coated with a hydrophilic polymer colored black to eliminate the photosensitivity of the PH-ISFET is a practical problem. The inventors used PH-ISFET.
The present invention was arrived at as a result of extensive research aimed at providing a practical gas sensor that eliminates the photo-sensitivity of Severinghaus type gas sensors. That is, the gas sensor of the present invention includes a hydrogen ion sensitive FET converter having an elongated gate insulated field effect transistor structure having a gate portion at one end and an electrode portion at the other end, and a hydrogen ion sensitive FET converter provided adjacent to the gate portion of the converter.
FET with Ag-AgCl reference electrode and lead wire connected
An insulated tube that accommodates a converter and a reference electrode, a FET converter and a reference electrode that are positioned in an opening provided in the insulated tube, a lead wire extended along the tube, and a connector connected to the other end of the lead wire. However, at least the electrical insulating resin filled between the inner wall of the tube and the lead wire connection part to close the tube, and the gas coated across both the gate part of the FET converter and the reference electrode can be absorbed to absorb hydrogen. A hydrophilic polymer layer containing an electrolyte with varying ion concentration and a transmittance of 10 for light in the wavelength range of 400 to 1200 nm covering the entire surface of the insulating tube containing the hydrophilic polymer layer and at least the FET converter. % or less, and the quotient (p/d) of the nitrogen gas permeability coefficient (p) by the film thickness (d) is 2.5×10 ^-7 [cm ³
(STP)/ ^cm2・sec・cmHg] A film containing carbon black that satisfies the following formula and has a thickness of 10 μm or more
This gas sensor consists of a gas permeable membrane made of 200μm black silicone rubber. 0.01≦dc/s≦0.50, c≦0.50 where d is the film thickness of the silicone rubber (μm), s is the body area average particle diameter (Å) of carbon black contained in the silicone rubber, and c is the Weight fraction of carbon black. Next, an embodiment of the gas sensor of the present invention will be described with reference to the drawings. Figure 1 is used in the gas sensor of the present invention.
FIG. 2 is a plan view showing an example of a PH-ISFET. This PH
-ISFET 1 is elongated and has a width of 0.4 mm and a length of 3 to 4 mm, for example, and has a gate portion 2 at one end, and a drain terminal 3 and a source terminal 4 at the other end. As shown in FIG. 2, which is a cross-sectional view taken along the line A-A in FIG. Constructed by sequential coating. This surface stabilizing film 10 includes silicon nitride (Si ₃ N ₄ ),
Alumina (Al ₂ O ₃ ), tantalum pentoxide (Ta ₂ O ₅ )
One of the following membranes can be used, and a sensor having such a membrane is sensitive to hydrogen ions. Actual surface stabilization film
If a silicon nitride film of about 1000 Å is used, the pH will be 1~
In the PH range of 13, an interfacial potential of 53 to 56 mV/PH, which is almost the same as that of conventional glass electrodes, can be obtained. Figure 3 shows the structure of the present invention using the above PH-ISFET.
Cross-sectional view of a Severinghaus type gas sensor, which includes polyethylene, polypropylene, polytetrafluoroethylene, silicone,
A flexible insulating tube 11 made of nylon 11, polyvinyl chloride, polyethylene terephthalate, etc., such as Ag-AgCl at the tip of a catheter that can be inserted into a living body.
A comparison electrode 12 made of a wire and a PH-ISFET 1 are housed separately from each other. The above reference electrode is made by JP-A-Sho.
As shown in No. 57-40641, Ag−AgCl is PH−
It may be deposited on the surface of the ISFET. Above Ag
A part of the -AgCl comparison electrode and the gate part 2 of the PH-ISFET 1 are housed in an exposed state in the opening at the tip of the insulating tube 11. Each lead wire 13 connected to the reference electrode 12 and the PH-ISFET 1 is insulated and led out from the rear end (not shown) through an insulated tube. Note that the opening at the tip of the insulating tube 11 is for PH-ISFET.
In order to protect 1 from damage, it is made to protrude slightly from this point and is cut out diagonally so that it can be easily inserted, for example, into a living body. And PH-
An electrical insulating resin 14 is inserted between the lead wire connection part of the ISFET 1 and the Ag-AgCl reference electrode 12 and the inner wall of the insulating tube.
For example, at least the tip of the insulating tube is closed by filling it with epoxy resin or silicone resin. It is preferable that the electrically insulating resin is filled throughout the interior of the insulating tube. FIG. 4 shows another example of the gas sensor of the present invention, in which Ag
-AgCl reference electrode 12 and PH-ISFET 1 are accommodated. Then, the opening of the insulating tube is closed by filling the tube with electrically insulating resin 14, leaving a space formed by the opening, the gate part 2 of the PH-ISFET, and a part of the comparison electrode. By absorbing gas across both the gate part 2 of PH-ISFET 1 and the comparison electrode 12.
Hydrophilic polymer layer 1 containing electrolyte with changing pH
5 is provided. The thickness of this polymer layer is preferably 1 to 10 μm in a dry state. When the thickness of the polymer layer is 10 μm or more, the response speed decreases.
Furthermore, the signal becomes unstable below 1 μm. Therefore, the polymer layer needs to be thin and uniform. The polymer used here has moderate water absorption (more than 60% by weight at a measurement temperature of 37°C) and is substantially free of organic acid groups and base groups such as COOH groups, in other words less than 2 mol% (based on all monomer units). ) is important. If the water absorption is low, the response speed will be low, and if it contains organic acid groups or basic groups, the sensitivity will be decreased. Such polymers include polyvinyl alcohol (hereinafter referred to as PVA), cellulose, polyhydroxyethyl methacrylate,
Examples include polyvinylpyrrolidone, agar, starch, and electrolyte polymers. These polymers may be copolymerized with other monomers and may also contain plasticizers and the like. Among these polymers, PVA is particularly superior in terms of stability. Furthermore, if the electrolyte contained in this polymer layer has a low concentration relative to the polymer, sensitivity tends to decrease and the signal becomes unstable. Moreover, if the concentration is large, the response speed will decrease. Therefore, it is necessary to contain the electrolyte in an amount that does not cause the above-mentioned troubles.
For example, in the case of a carbon dioxide sensor, add 0.01 to 1 mol of NaHCO ₃ and 0.1 to 1 mol of NaCl to the polymer aqueous solution.
It is preferable to include 2Mol. A polymer layer containing such an electrolyte may be formed by dissolving the polymer and the electrolyte in a solvent such as water, applying the solution, and drying the solution. Alternatively, a solution of the polymer alone may be applied in advance, or a polymer layer obtained by polymerization on the gate may be crosslinked if necessary, immersed in an electrolyte to swell, and then dried. In either case, freeze-drying is preferred in order to maintain the thickness of the swollen state. The hydrophilic polymer layer 15 is further coated with a gas-permeable colored silicone rubber 16. In order for the above gas permeable membrane to always show stable and accurate measurement values for a long time without being sensitive to light, the gas permeable membrane must (1) have a 90% response time of the gas sensor of less than 120g; (2) The light sensitivity of the gas sensor shall be 1 mV or less for 2000 Lux white light. It is necessary to have the performance of Note that the 90% response time of a gas sensor means that the output of the gas sensor is 90% of the equilibrium value from the moment the gas sensor is moved from 37°C or below and 36 mmHg to 72 mmHg partial pressure.
is defined as the time it takes to reach . The output of the gas sensor is the displayed value of the partial pressure of the gas. Further, the photosensitivity of the gas sensor is measured as follows. PH at a distance where the illumination intensity is 2000Lux from the tungsten lamp
-Place the gas sensor in the direction where the ISFET gate face faces the lamp and take out the output of the gas sensor as the source potential. The drain current is fixed at 30μA. The difference in the output of the gas sensor when the gas sensor is irradiated with the tungsten lamp and when it is not is taken as the optical sensitivity of the gas sensor. In order to search for a gas-permeable membrane that satisfies the above two conditions, the present inventors investigated fluorocarbons such as tetrafluoroethylene, trifluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, etc., which are conventionally well-known gas-permeable membranes. polymers and copolymers, polyethylene, polypropylene,
Light transmittance and gas permeability were investigated by adding dyes or pigments to polyolefins such as polypentene-1 and silicones. As a result, when a pigment is added to a polymer, the light transmittance decreases, but the gas permeability also decreases at the same time, so silicone rubber, which originally has high gas permeability, has sufficient gas permeability even after adding the pigment. is advantageous. In order to satisfy the above-mentioned requirements for the silicone rubber as a gas sensor, that is, 90% response time of 120 seconds or less and photosensitivity of 1 mV/2000 lux or less, the nitrogen gas permeability at room temperature must be 2.5 x 10 ^-7 cm. ³
(STP)/ ^cm2・sec・cmHg or more and 400 to 1200
PH-
It has been found that the photosensitivity of ISFET can be eliminated. The nitrogen gas permeability described above is based on a membrane area of 1 cm ² ,
The volume of nitrogen gas permeating through the membrane in 1 second when the nitrogen gas partial pressure difference between the two sides of the membrane is 1 cmHg is converted to the volume under standard conditions (STP; 0° C., 1 atm). Furthermore, the permeability of nitrogen gas is 2.5×10 ^-7
cm ³ (STP)/cm ²・sec・cmHg or more and 400~
It has been found that a silicone rubber film having a transmittance of 1200 mμ of light of 10% or less is a carbon book-containing silicone rubber film that satisfies the following conditions (1), (2), and (3). 10≦d≦200 (1) 0.01≦dc/s≦0.50 (2) c≦0.50 (3) Here, s is the body area average particle diameter of carbon black expressed in angstroms, and d is the diameter of the silicone rubber film. The thickness is expressed in micrometers, and c is the weight fraction of carbon black in the silicone rubber film. The body area average particle diameter of carbon black is (4)
Defined by Eq. d=Σnidi ³ /Σnidi ² (4) where di is the particle diameter (Å) of each carbon black particle observed with an electron microscope, and ni is the number of particles with particle diameter di. di is separated into 50 angstrom intervals. Equation (1) indicates the range of thickness of the silicone rubber film used in the gas sensor of the present invention. That is, the thickness of the silicone rubber film needs to be in the range of 10 μm to 200 μm. If the thickness of the silicone rubber film exceeds this range, the gas permeability will be too low. Furthermore, the outer diameter of the entire sensor becomes too large, which is undesirable because, for example, when the sensor is placed in a patient's blood vessel, the patient will experience great pain. If the thickness is less than the above range, pinholes are likely to be formed in the film and the mechanical strength is reduced, which is not preferable. Equations (2) and (3) define the range of carbon black content in the silicone rubber film. In other words, the carbon black content is from 0.01s/d to 0.5s/d.
It is necessary that d is within the range, and c is within the range of not exceeding 0.5. Carbon black content is
If it falls below the range of formula (2), the light transmittance at 400 to 1200 mμ will be 10% or more, which is not preferable. Furthermore, if the content of carbon black exceeds the range of formula (2), the gas permeability of the silicone rubber membrane will decrease, and the silicone rubber membrane may become difficult to mold, or even if it can be molded, its mechanical strength will be insufficient. This is not desirable because it becomes a problem. The gas permeable membrane 16 is coated with a third layer using a method such as dip coating or spray coating.
It can be coated as shown in Figure b. The gas permeable membrane needs to be uniform and thin in order to obtain a sufficient response speed. To this end, as shown in FIG. 3a, a gas-permeable tube whose tip is closed with the colored silicone rubber 17 can be used to cover at least the entire PH-ISFET surface of the insulating tube.
In addition, in a sensor with an opening in the side wall of the insulating tube, the fourth
As shown in the figure, the insulating tube can be coated with tube-shaped silicone rubber. This method is a preferred method because it allows the gas sensor to be miniaturized in the case of an elongated sensor. The hydrophilic polymer layer of the gas sensor produced in this way is dry and will not work as it is, so the sensor is used after the hydrophilic polymer absorbs moisture and swells in water or steam. Even if this sensor is once dried, it can be used again by immersing it in water for a long time, but it is preferable to store the sensor in water for immediate use. FIG. 5 is an example of a gas sensor housed in a storage container for preliminarily absorbing moisture and swelling a hydrophilic polymer. This gas sensor includes a catheter section 20 that houses a PH-ISFET and an Ag-AgCl reference electrode protruding from the tip of a flexible tube, a connector 22 to which a lead wire 13 is connected, and a connector 22 that is attached to the end of the catheter section. It consists of a stopper 23, a sheath-like protection tube 24 into which the catheter section is inserted, and a rotation lock 25 that brings the stopper and the protection tube into fluid-tight contact. As shown in Fig. 3, the catheter section 20 has a PH-ISFET and an Ag-
An AgCl reference electrode is housed. A lead wire 13 connected to the PH-ISFET and the reference electrode extends along the inner wall of the tube and is taken out from an opening at the other end of the tube. The connector 22 is provided with a plurality of connector pins 21, and the above-mentioned lead wires are connected to the pins with solder 2.
Connected by 6. The lead wire connection side of the connector is formed into a cylindrical shape, and a pin is fixed therein. A screw 27 is provided on the outer periphery of the columnar shape. The plug body 23 has a cylindrical shape, and the catheter portion 20 is inserted through the plug body. One end of the plug is screwed into the connector 22 by a screw 27. The internal space of the cylindrical plug body is filled with electrically insulating resin 2.
8, and the end of the tube forming the catheter section 20 and the lead wire are embedded and fixed therein. A rotation locking flange 29 is provided at the other end of the stopper, into which a cylindrical rotation lock 25 is fitted. The end of the rotary lock 25 is configured to be locked by the flange 29 mentioned above. Further, a helical protrusion 30 is provided on the inner periphery of the cylindrical rotating lock. The protection tube 24 is made of heat-resistant resin and has a sheath-like shape with one end closed, and the opening of the protection tube engages with a helical protrusion 30 provided on the inner periphery of the rotary lock 25. A matching rotary lock receiver 31 is provided. This protective tube contains a solution 32 in which conjugate ions for the gas to be detected are dissolved. The conjugated ions placed in the protective tube are base ions that have a conjugate relationship with the gas if it is acidic,
If the gas is basic, it means an acid ion in a conjugate relationship with it. For example, in the case of a CO ₂ sensor, conjugated ions are HCO ₃ ^- and CO ₃ ^2- ions. Solutions containing these ions are, for example, NaHCO ₃ ,
_KHCO3 , ( _NH4 ) _HCO3 , _{Na2CO3 , K2CO3 ,}
It can be prepared by dissolving salts such as (NH ₄ ) ₂ CO ₃ in a solvent. For _SO2 sensor, the conjugated ion is
Since HCO ₃ ^- and SO ₃ ^2- , NaHSO ₃ , KHCO ₃ ,
( _NH4 ) _HCO3 , _{Na2CO3 , K2CO3 , ( NH4} ) _2CO3
etc. may be used. In the case of a NO ₂ sensor, there are two types of conjugated ions, NO ₃ ^- and NO ₂ ^- , and a solution containing at least one of these may be used. Such solutions include, for example, NaNO ₃ , KNO ₃ ,
It is prepared by dissolving at least one salt among NH ₄ NO ₃ , NaNO ₂ , KNO ₂ , and NH ₄ NO ₂ in a solvent. Similarly, in the case of halogen gas sensors, for example, NaX, KX, _NH4X , NaXO, KXO,
A desired solution is prepared by dissolving at least one salt of NH ₄ XO (X=Cl, Br, I) in a solvent. A solution containing these conjugated ions is used as an electrolytic solution contained in a hydrophilic polymer that constitutes a gas sensor. The composition of the solution placed in the protective tube may be the same as that of the solution used as the electrolytic solution, but it does not necessarily have to be the same. for example
For _CO2 sensors, the electrolyte is usually _NaHCO3
An aqueous solution containing NaCl and CO ₂ is used.
A solution having the same composition as above may be used as the solution to be placed in the protective tube of the sensor, but an aqueous solution containing only NaHCO ₃ or an aqueous solution containing only KHCO ₃ may also be used. The concentration of conjugated ions contained in the above-mentioned conjugated ion solution is usually in the range of 0.01 to 5 mol/.
Further, as a solvent for this solution, a polar solvent such as water, ethylene glycol, diethylene glycol, propylene glycol, propylene carbonate, or a mixed solvent thereof is used. After placing the catheter in a protective tube containing an aqueous solution so that the sensitive part of the sensor attached to the tip of the catheter is immersed in the aqueous solution, the rotary lock 25 provided on the stopper is used to open the protective tube. The open end of the protection tube is attached to the side surface of the flange 29 provided on the stopper by engaging with the rotation lock receiver 31 provided at the end.
Furthermore, the stopper 23 and the protective tube 24 can be connected in a liquid-tight manner by bringing the end of the rotary clock into close contact with the other side of the flange. The gas sensor housed in the protection tube is subjected to high-pressure steam sterilization and then stored in a wet state. The sensor taken out from the protective tube is inserted into the indwelling catheter 3 inserted into the blood vessel 33, as shown in FIG.
It is inserted within 4. By engaging the rotation lock 25 with the flange 35 provided on the indwelling catheter, the gas sensor can be inserted into the indwelling catheter in a fluid-tight manner. The connector pin 21 of the gas sensor is connected to a monitor (not shown), and the seventh
The gas concentration in blood can be measured by the circuit shown in the figure. This circuit is a source follower circuit, and the comparison electrode 12 is grounded. A constant voltage V _D is applied to the drain 6 , and a constant current flows between the drain 6 and the source 7 by a constant current circuit 36 . When the gas sensor is inserted into a liquid to be measured, for example, a blood vessel, the gas that has passed through the gas permeable membrane 16 is absorbed by the electrolyte contained in the hydrophilic polymer layer 15, changing the hydrogen ion concentration of the electrolyte and causing the polymer layer to The interface potential of the exposed gate portion 2 of the PH-ISFET 1 is changed. As the interface potential changes, the source potential V _S changes. Therefore, output terminal 3
By measuring the potential between the reference electrode 7 and the reference electrode 12, the hydrogen ion concentration in the polymer layer, in other words, the gas concentration in the solution can be measured. Example 1 PH shown in Figure 1 with Si ₃ N ₄ in the gate sensitive film
- An Ag-AgCl reference electrode prepared by chlorinating an ISFET (length 5 mm width 400 μ) and a silver wire was embedded in the tip opening of a nylon catheter (diameter 0.6 mm), and a PVA aqueous solution containing NaHCO ₃ was applied onto it. Furthermore, eight types of colored silicone with a thickness of 100 μm and different carbon black contents were made using carbon black with a body area average particle diameter of 720 Å and silicone RTV, and these were coated on the surface of the PVA film. A carbon dioxide sensor shown in FIG. 3b was manufactured. Table 1 shows the performance of the eight types of gas sensors mentioned above.

[Table] As the carbon black content in the silicone rubber film increases, the light transmittance (value at a wavelength of 800 nm)
decreases, and the light sensitivity of the PCO ₂ sensor decreases. When carbon black is about 10 wt% or more, the transmittance at 800 nm is less than 10%, and accordingly, the light sensitivity of the PCO ₂ sensor is less than 1 mV/2000 lux. On the other hand, the permeation rate of nitrogen gas decreases as the carbon black content increases, and at 50 wt%, the permeation rate of nitrogen gas decreases to 2.9 × 10 ^-7 cm ³ /
^cm2・sec・cmHg. At this time, the PCO ₂ sensor
The 90% response time is 110 seconds, which is suitable for practical use. However, when the content of carbon black exceeds 60 wt%, the mechanical strength of the resulting silicone rubber film is extremely low, making it unsuitable for practical use as a PCO ₂ sensor. Example 2 Ten types of blackened thicknesses with different carbon black contents with a body area average particle diameter of 120 Å
A carbon dioxide sensor shown in FIG. 3b was manufactured in the same manner as in Example 1 using a 102 μm silicone rubber membrane as a gas permeable membrane. Table 2 shows the performance of the 10 types of carbon dioxide sensors mentioned above.

[Table] In this case, since the particle size of carbon black is smaller than that used in Example 1, the light transmittance from 400 to 1200 mμ is 10% or less when the carbon black content is 1.5 wt%. In this case as well, if the carbon black content is 60 wt% or more, the mechanical strength of the silicone rubber film becomes so low that it becomes unusable. Example 3 Table 3 shows the performance of a carbon dioxide gas sensor similar to Examples 1 and 2, which was manufactured using a 180 μm thick silicone rubber film blackened with carbon black having a body area average particle diameter of 120 Å.

[Table] In this case, the thickness of the silicone rubber film is approximately 1.8 times that of Example 2. Therefore, when the carbon black content is 0.7wt%, the light transmittance is already less than 10%. On the other hand, as the film thickness increases, the gas permeability decreases, and for this reason, when the carbon black content is 40 and 50 wt%, the gas permeability is 2.5 × 10, although the mechanical strength of the silicone rubber film is sufficient. ^-7 cm ³ /cm ²・sec・cmHg or less,
90% response time as a PCO ₂ sensor exceeds 120 seconds. Example 4 An aqueous solution containing 0.1M NaHCO ₃ was placed in the protective tube shown in FIG. 5, and the carbon dioxide catheter part shown in FIG. 3a was inserted into the tube and the tube was tightly plugged. The thus sealed carbon dioxide gas sensor was subjected to high-pressure steam sterilization at 120° C. for 1 hour, and then allowed to cool to room temperature, after which the catheter portion was taken out from the protective tube. PH−
The tip of the catheter section containing the ISFET and reference electrode was equilibrated with 5% (36 mmHg) CO ₃₇
It was immersed in water at a temperature of .degree. C., and the change in source potential over time was measured using the circuit shown in FIG. After soaking the result
The source potential drifts after 10 minutes, 1 hour, and 24 hours were +5 mV, +5 mV, and +6 mV, respectively. That is, the drift of the carbon dioxide sensor subsided within 10 minutes after the start of measurement, and the subsequent drift was +1 mV over 24 hours. Comparative Example Simply distilled water was placed in the protective tube shown in Fig. 5, and the catheter part of the carbon dioxide sensor similar to that in Example 4 was inserted into the tube, and after sealing the tube, Example 1
The same sterilization was performed. After sterilization, the protective tube was allowed to cool to room temperature and the change in source potential was measured under the same conditions as in Example 1. The drift values of the source potential were +45 mV, 10 minutes, 1 hour, and 24 hours after the start of measurement, respectively. They were +92mV and +143mV.

[Brief explanation of drawings]

Figure 1 shows the PH- used in the gas sensor of the present invention.
This is a plan view of ISFET, and Figure 2 is shown in Figure 1.
3 and 4 are cross-sectional views of essential parts of the gas sensor of the present invention; FIG. 5 is a cross-sectional view of the gas sensor housed in a protective tube; and FIG. 7 is a sectional view showing a state in which the gas sensor of the present invention is inserted into a blood vessel, and FIG. 7 is an electrical circuit diagram using the gas sensor of the present invention. 1...PH-ISFET, 2...Gate section, 3...
Drain terminal, 4... Source terminal, 11... Insulating tube, 12... Ag-AgCl reference electrode, 13... Lead wire, 15... Hydrophilic polymer layer, 16... Gas permeable membrane (colored silicone rubber) .

Claims (1)

[Scope of Claims] 1. A hydrogen ion sensitive FET converter having an elongated gate insulated field effect transistor structure having a gate portion at one end and an electrode portion at the other end; An Ag-AgCl reference electrode, an FET converter with lead wires connected to it, and an insulated tube that houses the reference electrode, and the FET converter and reference electrode are placed in the opening provided in the insulated tube, and the lead wires are placed along the tube. An electrical insulating resin that extends and connects a connector to the other end of the lead wire, fills at least between the inner wall of the tube and the lead wire connection part to close the tube, and both the gate part of the FET converter and the reference electrode. a hydrophilic polymer layer containing an electrolytic solution whose hydrogen ion concentration changes by absorbing gas, and a hydrophilic polymer layer containing an electrolyte whose hydrogen ion concentration changes by absorbing gas, and at least a FET
The entire surface of the insulating tube containing the transducer is coated.
The transmittance of light from 400 to 1200 nm is 10% or less, and the quotient (p/
d) is 2.5×10 ^-7 [cm ³ (STP)/cm ²・sec・cmHg]
A gas sensor comprising a gas permeable membrane made of black silicone rubber and having a thickness of 10 μm to 200 μm and containing carbon black that satisfies the following formula. 0.01≦dc/s≦0.50 c≦0.50 where d: Silicone rubber film thickness (μm) s: Body area average particle diameter of carbon black contained in silicone rubber (Å) c: Carbon black contained in silicone rubber Weight fraction.