JP2005214989A - Qcm sensor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problems in a measuring cell structure in a conventional QCM sensor device that need of position control for a reference electrode and a counter electrode which are separately provided leads to an increase in price and size, and the imbalance of the current force line carried from the counter electrode to a working electrode causes deterioration of measurement accuracy. <P>SOLUTION: This QCM sensor device comprises a reference electrode and a counter electrode 34 integrally fixed to a quartz substrate in addition to a working electrode and a back electrode thereto provided on the quartz substrate. The counter electrode is arranged in a position opposite to the working electrode through a gap, whereby the potential distribution can be uniformed to enhance the measurement accuracy. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention detects adsorption / desorption of sample components on the surface of the working electrode from changes in the electrical characteristics such as the oscillation frequency and impedance of the crystal when the working electrode surface of the quartz crystal is exposed to the sample gas or sample solution. -It relates to a QCM (Quartz Crystal Microbalance) sensor device for quantification.

  In recent years, chemical and biosensors that apply the microbalance principle using AT-cut quartz resonators have attracted attention. The main resonance frequency of the AT cut crystal resonator is inversely proportional to the plate thickness of the resonator. In this case, when a sample component is formed on the electrode surface of the crystal resonator or adsorption of a substance occurs, a frequency shift corresponding to the weight per unit plane area of the substance existing on the surface occurs.

  The QCM sensor is an application of the frequency shift phenomenon described above. Since the AT-cut quartz resonator has a stable frequency over a wide temperature range, a stable detection sensitivity can be expected. Substance detection is possible in real time. The relationship between the amount of adsorbed material and the amount of frequency shift is shown below.

The relationship between the mass change (electrode surface adsorption / desorption amount) Δm and the frequency change amount (frequency shift amount) Δf of the crystal resonator having the main resonance frequency f ₀ is expressed by the following equation (1). It is represented by the Sauerbery equation.

Δf: frequency change amount, f ₀ : main resonance frequency of crystal resonator, A _PIEZO : electrical effective area (electrode area), μ _q : shear elastic constant of crystal, ρ _q : density of crystal, Δm: on electrode surface Resulting mass change (adsorption / desorption amount of electrode surface)
Here, the resonance frequency of the AT cut crystal resonator is expressed by the following equations (2) and (3).

ν: speed of sound in crystal, t _q : thickness of crystal,
Further, the Sauerbery equation expands the relationship between the main resonance frequency and the crystal thickness, and becomes the following equation (4).

In the above equation (4), C _f is the overall sensitivity.

  When this is used in the liquid, the frequency change amount Δf is also affected by the viscosity and density of the liquid, and is rewritten as the following equation (5).

η _L : Solution viscosity, ρ _L : Solution density, ω ₀ = 2πf ₀
The overall sensitivity C _f in this equation is expressed by the following equation (6).

As can be understood from the above equations, it is important to increase the main resonance frequency f ₀ in order to increase the overall sensitivity C _f . Further, since the overall sensitivity C _f itself is a function of frequency, the actual frequency change amount Δf depends on the square or 3/2 of the main resonance frequency f ₀ .

Therefore, the higher the main resonance frequency of the crystal resonator used as the sensor, the higher the sensitivity of the sensor. For example, FIG. 5 is a plot of the frequency shift amount Δf of a crystal resonator immersed in a 15 wt% (weight percent) glucose solution against the change in the main resonance frequency f ₀ . It can be seen that if the main resonance frequency f ₀ is high, the resonance frequency can be largely shifted due to vibration loss on the same electrode surface.

As described above, since the AT-cut quartz resonator uses the thickness slip mode, the main resonance frequency f ₀ is inversely proportional to the thickness t _q . In addition, in order to obtain a sufficient γ value (ratio of parallel capacitance to series capacitance in the equivalent circuit of a quartz crystal, usually less than about 250 with AT cut), the effective area of the electrode is proportional to the frequency. It is necessary to make it smaller. For the above reasons, a high-frequency crystal resonator is required to have a small electrode area and a thin crystal thickness.

  On the other hand, in order to realize a QCM sensor, a small crystal resonator can be supported without mechanical distortion, and the surface of the resonator is exposed to a sample gas or a sample solution. The apparatus is configured as shown in FIG.

  In the figure, a cylindrical sensor device housing apparatus body 1 made of an insulating material has an oscillation circuit section 2 screwed therein. A pair of contacts 3, 4 are provided with spring properties so as to protrude from the upper surface portion of the sensor device housing main body 1, and the other ends thereof are drawn out and connected to the oscillation circuit portion 2.

  A disk-shaped spacer 7 is provided at the periphery of the upper surface of the sensor device storage device body 1 by pins 5 and 6, and the crystal resonator 8 is sandwiched between the sensor device storage device body 1 and the spacer 7. Then, the electrode of the crystal resonator 8 is brought into contact with the tips of the contacts 3 and 4. For this sandwiching, O-rings 9 and 10 located on both sides of the peripheral portion of the crystal resonator 8 are used as a buffer and airtight structure. The screwed lid 11 is provided with a hole for pressing the spacer 7 against the sensor device housing main body 1 and exposing the upper surface of the crystal resonator 8 to the sample gas or the sample solution.

  The sensor device storage device main body 1 has a screwed lid 12 that covers the lower part of the sensor device storage device body 1 so as to be airtight, and a pipe 13 through which a signal line and a power supply line from the oscillation circuit unit 2 are passed.

  The storage device for the sensor device as described above has electrical characteristics due to the working electrode surface of the crystal resonator 8 being exposed to the sample gas or the sample solution, and the sample components being adsorbed and desorbed on the working electrode surface of the crystal resonator 8. As the change, for example, it is configured in a measuring apparatus that measures the change in the oscillation frequency of the oscillation circuit unit 2 as the change in the count value of the counter 14.

  In the solution-type electrochemical measurement, as shown in FIG. 7, the sensor device storage device 20 is immersed in a container 21 into which an electrolytic solution is introduced, and the components of the electrolytic solution are placed in the container 21 on the working electrode surface. Measurement with reference electrode (reference electrode) 22 for generating a reference potential for setting the potential of the working electrode and counter electrode 23 for adsorbing and desorbing the electrolyte component on the surface of the working electrode. A QCM measurement system is configured in which a cell configuration is used and a potentiogalvanostat (PGS) 24 is connected to these electrodes and electrodes (working electrodes) of a crystal resonator.

Furthermore, by forming a receptor corresponding to the component to be detected and quantified from the sample solution on the working electrode, for example, “anti-measles” for detecting and quantifying “measles” virus on the working electrode. By detecting and quantifying "Measles" and "Influenza" viruses in the sample components by immobilizing "Antivirus" and "Influenza antibodies" for detecting and quantifying influenza antibodies can do.
In addition, the thing of patent document 1 is well-known as a measurement of the physical property and electrochemical property of a fluid. In this document, only one electrode of the piezoelectric element is disposed so as to be in contact with the fluid in the flow cell to be a working electrode, and the counter electrode and the reference electrode are connected to a potential setting circuit and a current measurement circuit included in the flow cell. Flow cell type.
Japanese Examined Patent Publication No. 7-58249

  A conventional QCM measurement system using a QCM sensor device has a measurement cell configuration in which a sensor device storage device is immersed in a container, and a reference electrode and a counter electrode are positioned in the container. For this reason, the measurement cell provided with the reference electrode and the counter electrode and a device for attaching these electrodes is complicated and causes an increase in the size of the system configuration.

  In addition, if the relative position of the reference electrode and the counter electrode and the relative position of the sensor device storage device with the crystal resonator change every measurement, the measurement accuracy is affected. For this reason, an electrode mounting structure that can reproduce the relative position between these electrodes is required, and for example, an electrode position control mechanism that can control the movement of the electrodes in the X, Y, and Z axis directions is required.

  In particular, a high-frequency quartz crystal unit has a structure in which the electrode area is reduced. Therefore, a high-accuracy electrode position control mechanism is required for the position control of the reference electrode and the counter electrode, and an expensive electrode position control mechanism is required. To do.

  A conventional QCM measurement system using a QCM sensor device has a measurement cell configuration in which a sensor device storage device is immersed in a container, and a reference electrode and a counter electrode are positioned in the container. For this reason, the current force lines flowing from the counter electrode to the working electrode are uneven in the potential distribution and the uneven current force lines flowing in this way, the amount of the sample component deposited on the working electrode surface is biased at the electrode surface position. As a result, it appears as fluctuations in oscillation frequency, impedance, etc., and as a result, it is difficult to improve measurement accuracy.

  An object of the present invention is to provide a QCM sensor device that can be configured in a compact and low-cost measurement cell configuration and that can accurately define the relative position between electrodes, and that the potential distribution between the counter electrode and the working electrode is uniform. It is to provide a QCM sensor device that can be used.

The present invention is for detecting and quantifying the adsorption / desorption of a sample component on the surface of the working electrode from a change in the electrical characteristics of the quartz crystal when the working electrode surface of the quartz crystal is exposed to a sample gas or a sample solution. In the QCM sensor device,
In order to adsorb and desorb the sample components on the surface of the working electrode by forming electrodes facing the front and back surfaces of the quartz substrate and facing the working electrode exposed to the sample gas or sample solution with a gap. The counter electrode is provided and a reference electrode for generating a reference potential for setting the potential of the working electrode is provided around the working electrode and the counter electrode.

  According to the present invention, since the counter electrode and the reference electrode are fixed to the quartz substrate and integrally formed with the quartz substrate, the relative position between the electrodes can be accurately defined. In addition, since the counter electrode has a three-dimensional structure facing the working electrode with a gap, the potential distribution between the counter electrode and the working electrode can be made uniform to increase the measurement accuracy.

  FIG. 1 is a structural view of a QCM sensor device showing an embodiment of the present invention, and is a side sectional view of only a peripheral portion of a quartz substrate.

  The quartz substrate 41 is formed of an AT-cut quartz having a rectangular shape and a uniform thickness. The quartz substrate 41 is bonded to a quartz substrate 42 as a supporting substrate with a silicone adhesive or the like to support and lead out.

  In the quartz substrate 41, an electrode forming portion is dug by etching, and a circular working electrode 43A and its back electrode 43B are formed by a sputtering method or the like so as to face the front and back surfaces at the center of the dug portion. A lead portion is formed. The thickness of the digging portion of the quartz substrate 41 is the same as in the previous embodiments. The reference electrode 44 is formed in the vicinity of the working electrode 43 </ b> A on the surface of the quartz substrate 41. The configuration described above is substantially the same as that of the above-described embodiment.

Here, in this embodiment, it is set as the three-dimensional structure which made the counter electrode 45 oppose the working electrode 43A. The counter electrode 45 is a conductive metal plate bent into a substantially S shape when viewed from the side, and the support portion is supported by being bonded to the surface of the crystal substrate 41 and connected to the electrode lead portion 45 ₁ . The tip portion is substantially the same planar shape as the surface of the working electrode 43A, and is disposed to face the working electrode 43A with a gap.

  The planar structure of the tip of the counter electrode 45 has a circular shape equivalent to the working electrode 43A as shown in FIG. 2A, a hole provided in the center as shown in FIG. ) And a rectangular shape as shown in (d), but in order to equalize the potential distribution with the working electrode 43A, the planar shape of the working electrode 43A The structure shown in (a), (b), (d) of FIG.

  The QCM sensor device having the above structure is housed in a sensor device housing device as shown in FIG. 7 so that the electrodes 43A, 44, 45 are exposed to a sample solution or the like in order to constitute a QCM measurement system. As shown in FIG. 3, it is immersed in the container 21 as it is, and connected to the oscillation circuit 2 or potentiogalvanostat (PGS) 24 to measure changes in oscillation frequency.

  Therefore, the QCM sensor device of this embodiment can make the potential distribution between the working electrode 43A and the counter electrode 45 substantially uniform, and the amount of adsorption / desorption on the surface of the working electrode 43A is equalized at the position of the electrode surface. Measurement accuracy can be increased.

  FIG. 4 is a QCM sensor device structure showing another embodiment of the present invention. 1 differs from FIG. 1 in that a counter electrode 46 is formed on a quartz substrate (or a quartz substrate) 47 and one end of the quartz substrate 47 is sandwiched between spacers 48 and bonded to the quartz substrate 41 surface.

  According to this structure, as in the case of FIG. 1, the counter electrode 46 can be disposed opposite to the working electrode 43A with a gap, and in addition, the support of the counter electrode 46 is ensured, and the device In production, a quartz substrate on which a working electrode is formed and a quartz substrate on which a counter electrode is provided can be separately manufactured and product management is facilitated.

  In the structure of FIG. 4, the quartz substrate 47 can be bonded to the support substrate 42 with the spacers 48 interposed therebetween, and the reference electrode 44 can be provided on the surface of the quartz substrate 47 to obtain the same operational effects.

  The QCM sensor device shown in each of the above embodiments is provided with a quartz substrate on a support substrate such as quartz. Due to its structure, even if the QCM sensor device is directly immersed in a sample gas or sample solution, the working electrode side Since only the sample solution or the sample gas is exposed, the measurement can be performed using a compact storage device. In the measurement system using the storage device, there is an effect that a small amount of sample gas or sample solution is required for measurement compared to the conventional one.

  In addition, since the counter electrode has a three-dimensional structure facing the working electrode with a gap, the potential distribution between the counter electrode and the working electrode can be made uniform to improve the measurement accuracy.

1 is a structural diagram of a QCM sensor device showing an embodiment of the present invention. The top view of the counter electrode used by this invention. The block diagram of a QCM measurement system. FIG. 6 is a structural diagram of a QCM sensor device showing another embodiment of the present invention. The frequency shift characteristic view by a QCM sensor. The conventional sensor device storage apparatus figure. The conventional QCM measurement system figure.

Explanation of symbols

41 ... quartz substrate 42, 47 ... quartz substrate (support substrate)
43A ... Working electrode 43B ... Back electrode 44 ... Reference electrode 45, 46 ... Counter electrode 48 ... Spacer

Claims (1)

In a QCM sensor device for detecting and quantifying the adsorption / desorption of a sample component on the surface of the working electrode from a change in the electrical characteristics of the quartz crystal when the working electrode surface of the quartz crystal is exposed to a sample gas or a sample solution ,
In order to adsorb and desorb the sample components on the surface of the working electrode by forming electrodes facing the front and back surfaces of the quartz substrate and facing the working electrode exposed to the sample gas or sample solution with a gap. And a reference electrode for generating a reference potential for setting the potential of the working electrode around the working electrode and the counter electrode.

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