JPH0252250A - Chemical sensor - Google Patents

Abstract

PURPOSE:To enable response to an extremely trace quantity of adsorptive molecules with high sensitivity and high reproducibility by chemically modifying the surface of a frequency conversion element by a silane coupling agent or titanium coupling agent. CONSTITUTION:A surface acoustic wave element 1 is formed with an input converter 5 and an output converter 6 at a prescribed spacing on a quartz substrate 4. The converters 5, 6 are aluminum electrodes formed by etching and vapor deposition. The input signal is converted to surface acoustic wave by the converter 5 and propagates on the surface of the quartz substrate 4. The wave is returned to the electric signal by the converter 6 parted by a desired delay distance. The phase speed of the surface acoustic wave is delayed by the weight increase of a detecting part 8 and the oscillation frequency of the loop decreases in proportion to the adsorption quantity when a different chemical material is taken as the material to be adsorbed into the detecting part 8. The oscillation frequency restores the original value when the material to be adsorbed is detached. The absorption quantity and absorption/ desorption behavior of the material to be adsorbed to the detecting part 8 are monitorable if the change in the transmission frequency is measured by a frequency counter 3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a chemical sensor capable of detecting adsorption and desorption of minute amounts of chemical substances.

[Conventional technology]

In recent years, research has been conducted on chemical sensors in which an organic ultra-thin film is formed on a quartz crystal resonator or surface acoustic wave element, and the amount of a chemical substance adsorbed onto the organic ultra-thin film is measured.

First, as a chemical sensor using a crystal oscillator, for example, one in which a polymer film that adsorbs odorants is formed on the surface of a quartz crystal oscillator ("Sensor Technology", published by the Information Investigation Committee, 198
(May 1986 issue, page 7), a polyion complex type lipid membrane formed by a casting method consisting of a complex of a sulfone polymer and a quaternary amine (Chemical Society of Japan, 1933).
3rd year spring annual meeting lecture proceedings, page 899, lecture number 3
11F30), and those using polymer cast film (IEICE technical research report OMB-87-5
6, 1988) have been reported.

On the other hand, as a chemical sensor using surface acoustic wave elements,
A device that detects NO2 gas by forming a metal-free phthalocyanine thin film ([Published by Sensor Technology J Information Research Group, 1988
(June issue, p. 52), as well as those with various organic semiconductor films formed depending on the type of gas to be detected (Published by "Sensor Technology" Information Research Group, May 1988 issue, p. 39) [Problems to be Solved by the Invention] By the way, the various films used in these chemical sensors are mainly created by the casting method.
The film thickness is relatively thick at 0.2 to 0.5 μm.

However, these relatively thick films require time for chemicals that reach the surface of the film to diffuse into the interior and achieve adsorption equilibrium, and only a portion of the film thickness is available for adsorption. There are problems such as being uneconomical, difficult to quantitatively control the amount of adsorption, and insufficient sensitivity to detect minute changes such as those caused by ionic interactions. Many of these problems can be solved by reducing the film thickness, but it is impossible to reduce the film thickness any further than before using methods such as casting, and therefore it is difficult to improve the response speed. .

Therefore, an object of the present invention is to provide a chemical sensor with a fast response speed.

[Failure to solve the problem]

Instead of forming a relatively thick film as in the past, the present inventors chemically modified the surface of the frequency conversion element with a silane coupling agent or a titanium coupling agent to introduce an organic functional group. The inventors have found that the problem can be solved and have arrived at the present invention.

That is, the chemical sensor according to the present invention has a frequency converting element whose surface is chemically modified with a silane coupling agent or a titanium coupling agent, and the adsorption and desorption of a chemical substance to the frequency converting element is detected as a quantitative change in the oscillation frequency. It is characterized by detecting as follows.

First, as the silane coupling agent used in the present invention, one represented by the following general formula is used.

R, -3i-X In the formula, X1 to X3 are atoms or atomic groups that react with water to form a silanol group, and examples include C1, T,
OC1Hzt. 1 (however, j represents an integer from 1 to 6), -〇-COCH3, etc. X1 to X3 may be the same or different.

In addition, R1-R3 is a linear or side chain type saturated hydrocarbon group such as a methyl group, ethyl group, or octadecyl group, or a linear or side chain type unsaturated hydrocarbon group such as an allyl group, an ethynyl group, or a vinyl group. Hydrogen group, 3-aminopropyl group, 3-(2-
Nitrogen-containing hydrocarbon groups such as aminoethyl) aminopropyl group, sulfur-containing hydrocarbon groups such as γ-mercaptopropyl group, T
-Epoxy derivatives such as glycidoxypropyl groups, cyclic hydrocarbon groups or derivatives thereof such as phenyl groups and cyclohexyl groups, compounds in which a portion of the hydrogen atoms of saturated hydrocarbons are replaced with fluorine or chlorine, hydrogen sources, etc. Atoms or atomic groups selected from a wide range of The polarity and ionicity of these atoms or atomic groups can be varied by changing the length of the main chain, the presence or absence of unsaturated groups, or the introduction of different atoms other than carbon or hydrogen, so that the desired characteristics can be achieved. It may be selected as appropriate. Further, R1 to R3 may be the same or different.

Further, as the titanium coupling agent, various compounds in which the silicon atoms in the above-mentioned silane coupling agents are replaced with titanium atoms can be used.

For chemical modification, it is sufficient to simply dissolve the various coupling agents described above in an appropriate solvent and immerse a frequency conversion element such as a crystal resonator or a surface acoustic wave element in this solution for a predetermined period of time.

On the other hand, the substances to be adsorbed by the chemical sensor according to the present invention are not particularly limited, and include alcohol aldehydes, amides, amines, and ethers.

It can be widely selected from various organic compounds such as ketones and carboxylic acids, and simple element molecules such as halogen gas.

Can be done.

As described above, in the present invention, there is room for a wide range of choices in both the coupling agent and the adsorbed substance, but by devising a combination of these agents, the ability of the chemical sensor to identify the adsorbed substance can be varied in various ways. is possible.

For example, if you want to create a chemical sensor with high sensitivity to polar substances, it is desirable to use a highly polar coupling agent, and if you want to create a chemical sensor with high sensitivity to cationic substances, it is desirable to use a highly polar coupling agent. It is desirable to use an anionic coupling agent.ps0 Frequency conversion elements whose surfaces are chemically modified with the above-mentioned silane coupling agent or titanium coupling agent include crystal oscillators and surface These are elastic wave elements and the like. These frequency conversion elements are incorporated into a suitable oscillation circuit, and connected to a frequency counter such as a universal counter via an amplifier H or the like as required. In this way, adsorption and desorption of the chemical substance to the frequency conversion element can be detected as a change in the oscillation frequency according to the amount of the chemical substance. The hydroxyl groups and the like react with the functional groups of the silane coupling agent or titanium coupling agent and are covalently bonded to them. When a different type of chemical substance is adsorbed and desorbed by a frequency conversion element having a chemically modified surface in this manner, the oscillation frequency of the oscillation circuit in which the frequency conversion element is incorporated changes due to a change in weight.

For example, when the surface of a crystal oscillator, which is a piezoelectric element, is chemically modified, if different types of chemical substances are adsorbed, the oscillation frequency will decrease due to the increase in weight.

In addition, when the surface of the surface acoustic wave device is chemically modified,
When a different type of chemical substance is adsorbed, the phase velocity decreases and the delay time increases for the same reason, which also causes the oscillation frequency to decrease.

The chemical sensor according to the present invention is characterized in that the sensitivity to adsorbed substances is controlled by directly chemically modifying the surface of the frequency conversion element.

Unlike the conventional method in which an ultra-thin organic film is formed on a frequency conversion element, this method does not require a process for the adsorbed substance to diffuse through the film, making it possible to detect adsorption/desorption behavior with extremely high sensitivity. becomes possible.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

This example is an example in which the surface of a surface acoustic wave element was chemically modified using octadecyltrichlorosilane or allyltrimethylsilane as a silane coupling agent, and these were used to detect ethanol vapor.

FIG. 1 shows the configuration of a chemical sensor according to the present invention. The main components of the chemical sensor include a surface acoustic wave element (1) that uses surface acoustic waves as a delay line, a high frequency amplifier (2), and a frequency counter (3). The surface acoustic wave device (1) is formed by etching and vapor deposition on a crystal substrate (4) to form a pair of transducers 1, that is, an input transducer (
5) and an output converter (6) are formed at a predetermined interval. These input transducers (5) and output transducers (6) are specifically aluminum electrodes (7) formed by etching and vapor deposition, and their format is interdigital (interdigital), which has excellent electroacoustic efficiency in high frequency bands. This is a blind-shaped electrode. The width of the aluminum electrode (7) and the space between the electrodes as seen along the propagation direction of the elastic wave (represented by arrow X in the figure) are both 10 μm, so the period of the interdigital electrodes is 40 μm It is. Also, the crossing length is 3.2 mm. The distance between the input transducer (5) and the output transducer (6) is 12 mm, and the intermediate surface of these transducers is chemically modified with a silane coupling agent to form the detection section (8). There is. The input converter (5) and the output converter (6) each have two terminals, one terminal of the input converter (5) and one terminal of the output converter (
6) - side terminal is a high frequency amplifier (with an amplification factor of 40clB)
2) to form a loop with an oscillation frequency of 78.9 MHz, and is further connected to a frequency counter (3). The other terminals not used to form the loop are for grounding.

In a chemical sensor as described above, an input signal is converted into a surface acoustic wave by an input transducer (5), which propagates on the surface of a quartz substrate (4), and an output transducer separated by a desired delay distance. (6) is converted back into an electrical signal.

Now, when a different type of chemical substance is taken into the detection part (8) as an adsorbed substance, the weight of the detection part (8) increases, so the phase velocity of the surface acoustic wave slows down, and a loop occurs in proportion to the amount of adsorption. oscillation frequency decreases.

When the adsorbed substance is desorbed, the oscillation frequency returns to its original value.

By measuring such changes in the oscillation frequency with the frequency counter (3), it is possible to monitor the adsorption amount and adsorption/desorption behavior of the adsorbed substance to the detection section (8).

Here, chemical modification of the surface acoustic wave device was performed as follows. That is, 100μ of either octadecyltrichlorosilane or allyltrimethylsilane was added to 5
0rr+j! The surface acoustic wave device was immersed in this solution and kept at room temperature for 5 minutes while stirring. Next, they pulled up the surface acoustic wave device and incorporated it into the oscillation circuit described above to create a chemical sensor.

We conducted an experiment to detect ethanol using this chemical sensor. First, a filter paper impregnated with ethanol was placed in a suitable closed container, and the temperature was maintained at 20'C to saturate the inside of the closed container with ethanol vapor.

Next, the operation of leaving the chemical sensor in the airtight container and the operation of taking it out of the airtight container and leaving it in the air were repeated at regular intervals, and the adsorption/desorption behavior of citral was monitored using a frequency counter.

The results of this experiment are shown in FIGS. 2 and 3. Figure 2 corresponds to the case when octadecyltrichlorosilane treatment was performed, and Figure 3 corresponds to the case when allyltrimethylsilane treatment was performed. In each figure, the vertical axis represents frequency change (Hz), and the horizontal axis represents time (seconds). shows. Further, arrow A represents the timing at which the chemical sensor is brought into contact with ethanol-saturated air after being placed in the hermetic container, and arrow B represents the timing at which the chemical sensor is brought out of the hermetic container and brought into contact with air.

Looking at these figures, it is clear that both chemical sensors sensitively detect adsorption and desorption of ethanol. That is, these chemical sensors exhibit a behavior in which the oscillation frequency gradually decreases as ethanol is adsorbed, and the original oscillation frequency gradually recovers as the ethanol is desorbed, and their reproducibility is also excellent. These behaviors are more pronounced when treated with allyltrimethylsilane. this is,
Comparing the octadecyl group and the allyl group, which are the side chains of silane coupling agents, the latter has higher polarity due to the presence of double bonds and shorter chain length, and ethanol, which is a polar substance, has higher polarity. This is explained by the fact that it has a higher affinity for

〔Effect of the invention〕

As is clear from the above explanation, in the present invention, the surface of the frequency conversion element is chemically modified with a silane coupling agent or a titanium coupling agent to introduce various functional groups and increase the sensitivity to adsorbed substances. Can be adjusted. Therefore, unlike conventional methods using ultra-thin organic films, it is possible to respond with high sensitivity and high reproducibility to extremely small amounts of adsorbed molecules. Furthermore, chemical modification can be easily carried out by simply immersing the frequency converting element in a suitable coupling agent solution, which is extremely effective from the viewpoint of productivity.

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view showing the configuration of a chemical sensor using a surface acoustic wave device. Figures 2 and 3 are characteristic diagrams showing frequency changes when the chemical sensor of the present invention is applied to the detection of ethanol. Figure 2 shows the frequency changes when the surface acoustic wave element is treated with octadecyltrichlorosilane. Figure 3 corresponds to the case where allyltrimethylsilane treatment was performed. 1 ... Surface acoustic wave element 2 ... High frequency amplifier 3 ... 4 ... 5 ... 6 ... 7 ... 8 ... Frequency counter Crystal substrate input converter output converter Aluminum electrode Detection unit

Claims (1)

[Claims] A chemical device characterized by having a frequency converting element whose surface is chemically modified with a silane coupling agent or a titanium coupling agent, and detecting adsorption and desorption of a chemical substance to the frequency converting element as a quantitative change in the oscillation frequency. sensor.