JPS63250560A - Sensor for detecting material in liquid by acoustic wave - Google Patents

Abstract

PURPOSE:To improve the sensitivity of detecting the specific material in a liquid to be detected by providing paired electrodes for impressing an AC voltage and paired electrodes for generating an AC voltage onto the same surface of a substrate formed of a piezo-electric material which generates leak surface acoustic waves and the cut surface and providing a layer to adsorb the specific material between both. CONSTITUTION:The comb-shaped electrodes 111, 112 for input and the comb-shaped electrodes 121, 122 for output are provided on the same surface of the piezo-electric substrate 10 and a receptor 3 is provided between both the electrodes. An input signal generated by an oscillator 15 excites the leak surface acoustic waves on the substrate 10 by the electrodes 111, 112. The leak surface acoustic waves propagate in the substrate 10 and the receptor 3 and are converted to an electric signal by the electrodes 121, 122. The output signal thereof is compared with the input signal generated by the oscillator 15 in a phase comparator 16. The phase difference between the two signals is the propagation delay time of the leak surface acoustic waves between the electrodes 111, 112 and the electrodes 121, 122. The propagation speed of the leak surface acoustic waves changes when the specific material in the liquid 7 to be detected is adsorbed in the receptor 3. The change quantity of the phase is thus measured by the comparator 16, by which the detection of the specific material is permitted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a sensor that detects a substance forming a camellia in a liquid using leaky surface acoustic waves.

[Conventional technology]

Conventionally, a sensor for detecting a substance in a liquid using elastic waves has been a sensor that uses, for example, a bulk wave excited by a crystal oscillator and propagating in a solid.

An example thereof will be explained with reference to FIG. In the same figure, l is A
T-cut crystal resonator, 2 is a frequency counter, 3 is a receptor which is a thin film of material that adsorbs a specific substance, 4 is an oscillation circuit, 51 and 52 are input electrodes on the front and back surfaces of the crystal resonator l (not shown) Input leads connected to, respectively, 6! and 62 are the same (output electrodes on the front and back surfaces of the crystal resonator 1 (not shown)
These are the output leads connected to the respective output leads. 7 is the test liquid, 8
is the be force. With this configuration, when an alternating current is applied from the oscillation circuit 4 to the thickness direction of the crystal resonator 1 through the input leads 51 and 52, the crystal resonator 1 vibrates.

When the bulk wave propagates through the crystal resonator l, a potential difference is generated in the thickness direction of the crystal resonator l, and an alternating current is outputted to the oscillation circuit 4 through the output drawer 1 and 62. The resonant frequency repeats this closed loop.

Here, when the specific substance contained in the test liquid 7 is adsorbed by the receptor 3 on the surface of the crystal resonator 1, the mass of the receptor 3 increases. Therefore, as the mass of the surface portion of the crystal resonator l increases, the resonant wave number decreases. The original resonant frequency is fo, and the amount of decrease in the resonant wave number after increasing to 14 is Δf.
If the mass increase of the receptor 3 is ΔM, its area is A, and the mass increase per unit area is Δm, the following relationship holds true, where a is a proportionality constant.

Therefore, when a change in the resonant frequency appears on the frequency counter 2, it is known that a specific substance has been adsorbed to the receptor 3, and the presence of the specific substance in the liquid to be tested 7 can be confirmed. In addition, the resonance frequency decrease amount Δf is determined by the frequency counter 2.
By counting, the amount of the specific substance can be calculated using the above equation (1).

For example, if the substance to be detected in the test liquid 7 is an organic substance,
A substance that specifically binds to the organic matter is immobilized in the form of a thin film to form the receptor 3. For example, in order to detect an antigen as an immunosensor, an antibody is immobilized, and in the case of detecting an antibody, the antigen is immobilized. Generally, receptor 3 often uses proteins.

[Problem that the invention seeks to solve]

In the above-mentioned conventional sensor for detecting substances in liquid using bulk waves, the following method can be considered based on equation (1) as a method for increasing detection sensitivity. The method involves selecting a vibrator material with a large value of a, and increasing the resonant frequency Δf. There are three ways to increase the mass increase amount Δm per unit area.

However, when considering various factors such as temperature stability, it is difficult to select a resonator material with a large value of a, and the reality is that materials with a relatively small value are used. The frequency Δf is determined by the mechanical processing of the crystal, which is the piezoelectric material of the vibrator, so it cannot be set too high and is usually 100.
MH2 or less.

Furthermore, even if we try to increase the amount of mass increase Δm per unit area, there are not many types of materials that can adsorb specific substances.
Since the materials that can be selected for the receptor are limited, it is difficult to increase the mass increase per unit area. Due to these conditions, conventional sensors for detecting substances in liquid using bulk waves have a limitation in detection sensitivity, and have the disadvantage that they cannot be said to be practically sufficient.

The present invention has been made to eliminate the above-mentioned drawbacks.
The present invention provides a sensor that uses elastic waves to detect specific substances in liquid with extremely high sensitivity.

[Means for solving problems]

A sensor for detecting substances in liquid using elastic waves according to the present invention, which has been made to solve the above problems, will be explained with reference to FIG. 1 corresponding to an embodiment. As shown in the figure, in the sensor for detecting substances in liquid using elastic waves of the present invention, a counter electrode 111 to which an alternating current voltage is applied is placed on the same surface of a substrate 10 made of a piezoelectric material and a cut surface where leakage surface acoustic waves are generated.・112 and a counter electrode 1214122 that generates an alternating voltage are provided. And both counter electrodes Ill ・112
and counter electrode 12.・A layer 3 that adsorbs a specific substance is provided in the middle part between 122 and 122.

The counter electrode 1116112 is formed on the same surface of the substrate 10, and is, for example, a comb-shaped electrode. Counter electrode 12.・
122 is also formed on the same surface, and counter electrodes 11, ・11
The substrate IO, which preferably has the same shape as the counter electrode 11.2, is preferably of the same shape as the counter electrode 11. - An alternating current voltage is applied by 112 to excite the leaky surface acoustic wave, and a piezoelectric material and a cut surface that propagate with little propagation loss are selected. Examples of such piezoelectric materials include L 1Nb03 substrate, Li
A TaO3 substrate, quartz is preferred, and the cut plane angle is 1, for example, a 36° rotated Y-plate LiTaO3 substrate so that propagation occurs in the X direction.

[Effect]

In the detection sensor of the present invention, when an AC voltage is applied to the substrate 10 from the counter electrodes 111 and 112, a leaky surface acoustic wave with low propagation loss is excited by the substrate 10 and propagates on the surface of the substrate IO.

A leaky surface acoustic wave is a wave that propagates into a piezoelectric material while radiating some of its energy.

However, for example, in the case of propagation in the X direction of a 38° rotated Y plate LiTa0:+ substrate in contact with gas or vacuum, there is a field where the amount of energy radiated into the piezoelectric body is extremely small.
Per wavelength, S x 10-4 dB (when electrically short-circuited) and 3.8 x 10-5 dB (when electrically open).

In this way, the leakage surface acoustic waves are caused by the above-mentioned 36° rotated Y plate L 1Ta03 whose vibration displacement in the direction perpendicular to the substrate surface is sufficiently small.
In the case of the substrate, the vibration displacement in the direction perpendicular to the substrate surface is 1110 or less compared to the horizontal direction. Vibration in the direction perpendicular to the substrate surface contributes to energy radiation into the liquid when the substrate is in contact with liquid, so it is preferable to minimize the vibration. Since the displacement is small, less energy is radiated into the liquid and there is less propagation loss in the liquid.

In addition to the leaky surface acoustic waves mentioned above, surface acoustic waves in the Rayleigh wave mode are generated when an AC voltage is applied to piezoelectric materials such as L1Nb03 substrates, LiTaO3 substrates, and crystals using comb-shaped electrodes. exist. A Rayleigh wave mode surface wave is a composite wave of a displacement in the propagation direction and a displacement in a direction perpendicular to the surface, and is widely and commonly used as a surface acoustic wave filter or a surface acoustic wave resonator. Rayleigh wave mode surface waves are used in gas or vacuum, and in liquids, most of their energy is radiated into the liquid as they propagate, and there is a significant propagation loss. In the X direction propagation of a 128° rotated Y-plate LiNbO3 substrate, which is often used as a wave resonator, 0 per wavelength.
．． 99dB (when the surface is electrically shorted), 0
．． This is a large value of 84 dB (when the surface is electrically open).

The above comparison shows that leaky surface acoustic waves are superior to Rayleigh wave mode surface waves in terms of propagation loss in liquids.

The leaky surface acoustic waves excited by the input AC of the counter electrodes fiz 112 propagate on the layer 3 where the specific substance is adsorbed, and are converted into output AC by the counter electrodes 121 and 122. The phase difference between the input AC and the output AC is a delay due to propagation of the surface acoustic wave leaking through the surface of the substrate IO. Therefore, if the propagation time changes, the phase difference also changes. When a specific substance is adsorbed on the 0 layer 3, the mass of the surface portion of the 2S plate 1O changes, and the propagation speed of the leaky surface acoustic wave changes. By measuring this amount of phase change, it becomes possible to detect a specific substance.

If the amount of phase change is Δφ, the frequency of the input AC is fl, the propagation velocity of the leaky surface acoustic wave is V, and the amount of change in propagation velocity is ΔV, then the following relationship holds true (b is a constant), and the change in propagation velocity The quantity ΔV is calculated by the perturbation method regarding the leakage surface acoustic wave propagation velocity.

□〒cf Δm・・・・・・(4) (C is a constant) The relationship holds, therefore, Δφ=bcf+2*Δm=−−− (2).

This formula (2) is the calculation formula (1) when using the conventional configuration.
Compared to , the formulas are of the same type. The values of a and bc have specific values depending on the type of piezoelectric material that constitutes the substrate 10, but they are approximately the same.

The frequency f1 of the input AC is between the counter electrodes 1111el12 and 1
2+ ・Determined appropriately depending on the shape of 122.

If the counter electrodes 111, 112 and 121@122 are, for example, comb-shaped electrodes, the frequency f1 is currently several GH
It is possible to implement up to I. This frequency f1 can be made sufficiently higher than the resonant frequency fO in the case of the conventional configuration.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows an embodiment of a detection device using a sensor for detecting substances in liquid using elastic waves to which the present invention is applied.

In the structure of the figure, 10 is a piezoelectric substrate, 1116112 is a comb-shaped electrode for AC voltage input, 1210122 is a comb-shaped electrode for AC voltage output, and 3 is a receptor made of a thin film of material that adsorbs a specific substance. Yansa is composed. 15 is an oscillator.

16 is a phase comparator.

The input signal generated by the oscillator 15 is transmitted to the input comb-shaped electrode 1.
11 @112 excites a leaky surface acoustic wave on the piezoelectric substrate 10. The leaked surface acoustic waves propagate through the substrate lO and the receptor 3, and are converted into electrical signals by the output comb-shaped electrodes 121 and 122. This output signal is compared with the input signal generated by the oscillator 15 in a phase comparator 16.

The phase difference between these two signals is determined by the input comb-shaped electrode 111"l
12 and the output comb-shaped electrode 1216122 is the propagation delay time of the leaky surface acoustic wave. When the specific substance in the test liquid 7 is adsorbed by the receptor 3, the propagation speed of the leaked surface acoustic wave changes, and the amount of phase change can be measured by the phase comparator 16, making it possible to detect the specific substance.

FIG. 2 shows another embodiment of a detection device using an elastic wave sensor for detecting substances in liquid to which the present invention is applied.

Receptor 3, piezoelectric substrate 10, comb-shaped electrode 11+''l12 for AC voltage input. comb-shaped electrode 121 for AC voltage output.
The detection sensor of the present invention consisting of 122 is the same as the embodiment shown in FIG. 1, except that the circuit portion for detection is different: 19 is an amplifier, 20 is a phase shifter, and 21 is a frequency counter. . The electrical signals applied to the input comb-shaped electrodes 111 and 112 are converted into leaky surface acoustic waves, propagate on the receptor 3, and are transmitted to the output comb-shaped electrodes 121 and 1.
At step 22, the signal is converted back into an electrical signal. This electrical signal is
It passes through the phase shifter 20, is amplified by the amplifier 19, and is applied to the input comb-shaped electrode Ill.112. When the following relationship holds between the phase difference φa11 for one round in this loop, the amplification factor G of the amplifier 19, and other losses I in the loop, oscillation occurs as leaky surface acoustic wave oscillation.

φa++=2nπ (n is an integer) G>I This oscillation frequency is counted by the frequency counter 21. When the specific substance in the test liquid 7 is adsorbed by the receptor 3, the mass increases and the propagation speed of the leaky surface acoustic wave changes. This phase difference Δφ is ΔV Δφ=b'f2− (2) as in the embodiment shown in FIG. 1, and ΔV/V is expressed by the following equation.

ΔV −=c′ f 2Δm b”, Co is a constant, f2 is the oscillation frequency, and the phase between the input comb-shaped electrode 1116112 and the output comb-shaped electrode 121 and 122 is.

Since the phase is almost linear with respect to the frequency, the 6 oscillation frequency f2, which can be expressed as Δf, Δφ f2 °φ Δf:b'c'f2Δm, (5), can oscillate up to several GH2, and is specific substances can be detected with high sensitivity.

FIG. 3 shows another embodiment of a detection device using a substance-in-liquid detection sensor using elastic waves to which the present invention is applied. In the figure, 221 and 222 are input comb-shaped electrodes, 231 and 232 are output comb-shaped electrodes, 24 is an amplifier, and 25 is a phase shifter. Input electrodes 221 and 222, output electrodes 231 and 23
2. Construct a closed loop with an amplifier 24 and a phase shifter 25,
Use it as an oscillator.

This signal is input to the frequency counter 21 as a reference signal. Input electrodes 11+/112, output electrodes 12+/1
22, the amplifier 19, and the phase shifter 20, the only difference in the closed loop is the presence or absence of the receptor 3. Therefore, a change in frequency due to a change in the temperature of the substrate 10 or the like changes the frequency of the reference signal, and only the adsorption of the specific substance to the receptor 3 can be detected.

〔Effect of the invention〕

As described above, the sensor for detecting a substance in liquid using elastic waves of the present invention utilizes leaky surface acoustic waves, and has the advantage of significantly improving the sensitivity for detecting a specific substance in a sample liquid.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram of an embodiment of a device using a detection sensor to which the present invention is applied, and FIG. 2 is a block circuit diagram of another embodiment of a device using a detection sensor to which the present invention is applied. Figure 3 is a block circuit diagram of another embodiment,
FIG. 4 is a block circuit diagram of an embodiment of a device using a conventional detection sensor. 136. Crystal oscillator

Claims (1)

[Claims] 1. A counter electrode for applying an AC voltage and a counter electrode for generating an AC voltage are provided on the same surface of a substrate made of a piezoelectric material and a cut surface where leakage surface acoustic waves are generated, and a counter electrode for generating an AC voltage is provided between the two counter electrodes. A sensor for detecting substances in liquid using elastic waves, which is characterized by having a layer that adsorbs specific substances.