JPH01320450A - gas detection device - Google Patents

Abstract

PURPOSE:To prolong the life of a sensor by incorporating a non-volatile water soluble org. compd. (e.g.: hyaluronic acid or hyaluronic acid and polyhydric alcohol) into a detecting layer formed on the outside surface of a photoconductive medium to gel the layer. CONSTITUTION:The photoconductive medium 1 is, for example, a planar body consisting of glass which is provided with an incident light (LED) part 3 and a photodetecting (photodiode) part 4 in a part of one side face thereof. The other part thereof is covered with a light reflecting layer 5. As a result, the effect similar to the effect obtd. when a long fiber is used for the optical transmission part is obtd. The reflecting layer 5 is formed of the inorg. matter of Al or Au by vacuum deposition. The detecting layer 2 is formed by coating the compsn. contg. a detecting material and the non-volatile org. compd. as a layer on at least one face of the planar body 1. Natural high polymers such as hyaluronic acid and cellulose, synthetic high polymers such as polyvinyl alcohol and glycerol are adequate as the water soluble polymer used for formation of the layer 2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas detection device, and more particularly, to a gas sensor that can be applied in environmental conservation, medical fields, and the like.

4 The applicant first proposed that a polyhydric alcohol (e.g., glycerin) be used as a sensing layer that measurably changes the light transmission ability of a photoconductive medium upon contact with a specific substance (e.g., ammonia) in a gas. We proposed a gas sensing layer containing . As a result,
Although the sensitivity and response speed have improved compared to the conventional solid state dry sensing layer, the sensing layer gradually dries and the sensitivity and response speed have improved.
There was a drawback that the response speed decreased.

Purpose The present invention was made in view of the above-mentioned circumstances.
In particular, in an optical waveguide type ammonia sensor that utilizes the evanescent effect, the purpose is to extend the life of the sensor by gelling the sensing layer.

In order to achieve the above object, the present invention selectively reacts with a specific substance in a gas when it comes into contact with the substance to measurably change the light transmission ability of a photoconductive medium. A photoconductive medium having a detection layer containing a detection substance on the outer surface of the photoconductive medium, a light source disposed to transmit light to the photoconductive medium, and light emitted from the photoconductive medium. An optical detection device for detecting a specific substance in a gas is equipped with a means for measuring a specific substance in a gas, and is characterized in that the detection layer contains a non-volatile water-soluble organic compound.

The following is a description based on two embodiments of the present invention.

FIG. 1 is a perspective view for explaining one embodiment of a gas detection device according to the present invention, and FIG. 2 is a top view, in which 1 is a photoconductive medium, 2 is a detection layer, and 3 is an LED section. (light emitting part), 4
is the photodiode section (light receiving section).

Reference numeral 5 denotes a reflective part, and although a conventional optical fiber can be used as the photoconductive medium 1, a particularly preferable photoconductive medium is a plate-shaped body with a flat or curved surface, and at least one side of the plate-shaped body is has a structure covered with a light-reflecting layer. Particularly preferably, as shown in FIG. 2, the entire side surface is covered with a light reflecting layer 5 except that the incident light section 3 and the light receiving section 4 are provided on a part of the negative side surface. As a result, an effect similar to that obtained when a very long optical fiber is used as the optical conduction path, as shown by the second Uyi broken line, for example, can be obtained. As the photoconductive medium, optical materials such as inorganic materials such as glass and quartz, and organic polymers such as polymethyl methacrylate and polymethylpentene can be used. Further, the light reflecting layer 5 is made of Al1
．． An inorganic material such as Au or Ag can be formed by vacuum evaporation or the like.

The sensing layer 2 includes a substance (sensing substance) that selectively reacts with a specific substance in the gas and measurably changes the light transmission ability of the photoconductive medium, and a non-volatile organic compound. (For example, hyaluronic acid or hyaluronic acid and polyhydric alcohol) may be coated as a layer on at least one surface of the plate-like body.
Suitable water-soluble polymers used in the formation of are natural polymers such as hyaluronic acid, cellulose, and collagen, synthetic polymers such as polyvinyl alcohol, polyacrylamide, and polyethylene glycol, and glycerin. In particular, hyaluronic acid has a structure as shown in Figure 3, and 1 g of its salt is said to have the ability to retain approximately 6 a of water.

As shown in Table 1, the water retention properties of hyaluronic acid are not easily affected by relative humidity, unlike pyrrolidone carboxylic acid, sorbitol, and glycerin, making it particularly excellent as a humectant.

Table 1 (Moisture content (%) after standing for 32 hours) BK-7 plate (10 m x 10 wa x 0
, 5) and an LED (wavelength 660) as the incident light source.
nm), using a silicon photodiode as the light receiving section, as shown in Figure 2, six people set the incident light section 3 and the light receiving section 4 on one side of the photoconductive medium, and masked the light receiving section and both nail surfaces. 0-order bromothymol blue 0.3 wt%, polyvinyl alcohol 1wt%, water 65wt%, glycerin 33wt%, hyaluron. A coating solution consisting of 0.1 wt % potassium acid (Wako Pure Chemical Industries, Ltd.) was prepared and applied onto one surface of BK-7 using a spin cord (3000 rpm, 2 seconds) to produce a sensing layer on the gel. Bromothymol blue does not change color when exposed to air, but the presence of ammonia causes bromothymol blue to change color from green to blue, resulting in attenuation of the light transmitted through the photoconductive medium due to the evanescent effect.

Figure 4 shows the change over time in the sensitivity of the fabricated sensor with white circles (◯). The vertical axis shows the ratio of the output for air and the output when 1100 pp of ammonia gas was present in the air. For comparison, the measurement results with a sensor created by applying a coating liquid that does not contain potassium hyaluronate (other components are present in the same proportions) under the same conditions are shown in black circles. Clearly, no difference in sensitivity was observed depending on the presence or absence of potassium hyaluronate. Without potassium hyaluronate,
I (Nll,) / I (Air) increases rapidly in about 200 hours (sensitivity decreases for 100 ppm ammonia gas), whereas with potassium hyaluronate, the output does not change for almost 4000 hours. . This is because the presence of potassium hyaluronate keeps the sensing layer gelled.

Effects As is clear from the above explanation, according to the present invention, a nonvolatile water-soluble organic compound (for example, hyaluronic acid, or hyaluronic acid and polyhydric alcohol) is contained in the detection layer to form a gel. This makes it possible to extend the life of the sensor.

[Brief explanation of the drawing]

FIG. 1 is a perspective view for explaining one embodiment of the gas detection device according to the present invention, FIG. 2 is a top view, FIG. 3 is a diagram showing the structure of hyaluronic acid, and FIG. 4 is a diagram showing the present invention. FIG. 3 is a diagram showing changes in sensor sensitivity over time according to the invention. 1... Photoconductive medium, 2... Sensing layer, 3... LED
part (light emitting part), 4... photodiode part (light receiving part), 5... reflective layer. Figure 1 Figure 2 Section 3 Figure 4

Claims (1)

[Claims] 1. A sensing layer containing a sensing substance that selectively reacts with a specific substance in a gas to measurably change the light transmission ability of the photoconductive medium when it comes into contact with the specific substance in the photoconductive medium. a specific substance in a gas, comprising a photoconductive medium on the outer surface of the photoconductive medium, a light source arranged to transmit light to the photoconductive medium, and means for measuring light emitted from the photoconductive medium. 1. An optical detection device for detecting gas, characterized in that the detection layer contains a nonvolatile water-soluble organic compound.