JP2009031233A - Multi-channel qcm sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable a simultaneous measurement to be carried out stably by suppressing mutual interferences between channels. <P>SOLUTION: A grounded type oscillation circuit, which oscillates in such the state that one electrode of its oscillator X is grounded, is adopted as an oscillation circuit to be applied to a multi-channel QCM sensor, thereby preventing any electromagnetic wave from propagating to another channel and interfering with it although oscillations simultaneously take place on a plurality of channels. In the QCM sensor having two or more channels, one channel of the two or more channels is used as a measurement channel, and one channel is used as a reference channel, and a difference between the oscillation frequency of the measurement channel and the oscillation frequency of the reference channel is used as a sensing/quantitating frequency signal. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention provides a QCM that detects and quantifies a sample component from a change in electrical characteristics such as the resonance frequency and impedance of the vibrator when the electrode surface of the vibrator such as a quartz vibrator is exposed to a sample gas or a sample solution. In particular, the present invention relates to a multi-channel QCM sensor that simultaneously detects and quantifies a plurality of components from the same sample.

  In the fields of chemistry, biochemistry and electrochemistry, it is important to quantify the amount of reaction and the amount of product, but it was difficult to obtain sufficient detection sensitivity for very small amounts of reaction with conventional devices. .

  In recent years, chemical and biosensors that apply the microbalance principle using AT-cut quartz resonators have attracted attention. AT-cut quartz resonators exhibit a phenomenon in which the main resonance frequency is inversely proportional to the plate thickness of the resonator. When a sample component is formed on the electrode surface or when adsorption of a substance occurs, the unit of the substance present on the surface A frequency shift corresponding to the weight per plane area 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. Equation (1) shows the relationship between the amount of adsorbed material and the amount of frequency shift.

  First, the resonance frequency of the AT-cut crystal unit is

v _q is

It is represented by Where f _{0 is} the main resonance frequency of the crystal resonator, v _{q is} the propagation speed of the acoustic wave (transverse wave) of the thickness shear vibration, t _{q is} the thickness of the crystal resonator, μ _{q is} the rigidity of the crystal, and ρ _{q is} The density of the crystal.

  The resonance frequency change rate Δf due to the thickness change Δt of the crystal resonator having the main resonance is obtained from the equations (1) and (2):

It is represented by Further, the thickness change Delta] t of the crystal is Δt = Δm / ρ _q. Here, Δm is a mass change per unit surface area. When QCM is immersed in an aqueous solution, the density and viscosity of the solution are higher than in the gas phase. Therefore, the acoustic wave of thickness shear vibration is attenuated and transmitted to the solution side, and the resonance frequency is reduced. This can be regarded as equivalent to a state in which a liquid film layer having an effective thickness is formed on the quartz resonator. The effective thickness d ₁ of this liquid film layer is given by assuming that the aqueous solution is a Newtonian fluid.

Is approximated by Where v _{1 is} the kinematic viscosity of the aqueous solution, η _{1 is} the viscosity of the aqueous solution, ρ _{1 is} the density of the aqueous solution, f ₁ is the resonance frequency of the quartz crystal in the aqueous solution, and v ₁ = μ ₁ / ρ ₁ It is.

When QCM is used in a solution, only one side of the crystal unit is immersed in the solution in order to maintain insulation between both electrodes. When only one side of the crystal unit is immersed, the apparent mass change Δm ₁ per unit area of the electrode is expressed by the following equation (5) from equation (4).

Here, assuming that f ₁ = f ₀ and substituting the equation (5) into the equation (3), the resonance frequency change Δf when the crystal unit is immersed only in one side in the solution is

It is represented by As can be seen from the equation (6), it is important to increase the main resonance frequency f ₀ in order to increase the overall sensitivity. Therefore, the higher the main resonance frequency of the crystal resonator used as the sensor, the higher the sensitivity of the sensor.

Here, 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 . Therefore, a high-frequency crystal resonator needs to have a small electrode area and a thin crystal thickness. In the case where the quartz resonator is a thin quartz substrate corresponding to a high frequency, a method of thinning only the central portion of the substrate has been proposed.

  Further, the applicant of the present invention has already proposed a QCM sensor having a response cell with a higher response speed, in other words, a method of shortening measurement time, which is configured in a flow cell type and further multi-channeled (for example, Patent Document 1). reference).

  An example of the cell structure of this flow cell type multi-channel QCM sensor is shown in FIG. In the figure, the cell structure is shown by (a) a top view and (b) a side sectional view along the line A-A ′. Two channels of dug portions 12A, 12B, 12C, and 12D are formed on both surfaces of the mirror-finished quartz substrate 11 by a chemical etching method using hydrofluoric acid or the like. Electrodes 13A and 13C are formed on the bottom surfaces of both digging portions 12A and 12C, and electrodes 13B and 13D are formed on the bottom surfaces of the digging portions 12B and 12D, respectively, facing the electrodes 13A and 13C. The electrodes 13A to 13D have the same shape (radius) at the same facing position, and are connected to the external connection terminals 15A to 15D through the lead electrodes 14A to 14D, respectively.

  The surface shape of the digging portions 12A and 12B is set to a size (radius) that can form the electrodes 13A and 13B, and the shape of the digging portions 12C and 12D is a surface that can secure a flow path for flowing the sample gas or the sample solution. A structure with shape and depth. In the drawing, the digging portions 12C and 12D have a track-shaped plane whose central portion is a part of the electrodes 13C and 13D, one corner portion is a sample gas or sample solution injection portion, and the other corner portion is a portion of them. To the discharge part.

  According to the flow cell type multi-channel QCM sensor having the above-described structure, in addition to shortening the measurement time by the flow cell structure, the two-channel cell structure enables simultaneous measurement of two items with a single injection of the sample. Can be almost halved. In addition, the cell structure with two channels on one crystal substrate eliminates the variation between individual crystal units compared to the case of using two crystal units in parallel, and enables highly stable measurement. In addition, as compared with the case where the measurement is performed twice using one crystal resonator, there is no variation due to adjustment of the sample solution, and highly stable measurement is possible.

  FIG. 5 shows an assembly structure of a flow cell type multi-channel QCM sensor incorporating the crystal resonator shown in FIG. The crystal resonator 20 has, for example, a two-channel configuration of an integral cell structure in which a resonator portion is formed on a crystal substrate shown in FIG. 4 and a flow passage portion is formed by digging. The installation base (holding substrate) 21 is provided with guide pins 21A at the four corners, and with spring pins 21B for electrical connection at the inner periphery. The device positioning spacer 22 is provided with a notch 22A that can be fitted to the outer periphery of the crystal unit 20 at the center, and holes 22B that allow the guide pins 21A to be inserted with play at the four corners. It is stacked on the table 21. The quartz resonator 20 is placed on the installation base 21 in accordance with the notch 22A of the spacer 22, whereby the external connection terminals 15A to 15D drawn out on the back surface thereof are pressed against the spring pins 21B, respectively, to ensure electrical connection. .

  The silicone rubber packing 23 is placed on the crystal unit 20 with holes 23A for communicating the sample gas or the sample solution respectively on both sides of the digging portions 12C and 12D of the crystal unit 20. The The sample two-divided block 24 has holes 24A through which guide pins 21 are allowed to be inserted at the four corners, and openings at the sample inlet and outlet positions for two channels of the crystal resonator 20. The pipes 24B and 24C for collectively injecting the sample into these openings and discharging the sample from the openings are formed, and are placed on the quartz vibrator 20 from above the packing 23. Enable collective discharge.

  The pressure block 25 has holes 25 </ b> A through which the guide pins 21 are inserted at the four corners, and the spacers 22, the crystal unit 20, the packing 23, and the block 24 are stacked on the block 24. Pressurize with the weight.

4 shows a case of a two-channel structure, but a QCM sensor having a multi-channel structure of 4 channels or 9 channels has also been proposed (for example, see Patent Documents 2 and 3).
JP 2005-331445 A JP 2000-283905 A JP 2000-338022 A

  In a conventional multi-channel QCM sensor, the connection between a crystal resonator of each channel and an oscillation circuit that oscillates using the crystal resonator as a resonant element is switched at certain intervals to measure the oscillation frequency and the like for each channel. The purpose of this is to prevent the electromagnetic waves oscillated from the individual QCMs from propagating through and interfering with each other when the QCMs immersed in the same solution are simultaneously oscillated. As described above, in the method of measuring individual channels at a certain time interval, there is a limit to multi-channeling of about 8 channels at most due to the restriction of the necessary measurement data interval.

  In addition to mass addition, the QCM sensor is also known to be affected by changes in the viscosity of the solution and changes in the pH of the solution as shown in equation (6). QCM cells must be provided, and in this case, it becomes more difficult to increase the number of channels.

  An object of the present invention is to provide a multi-channel QCM sensor capable of suppressing mutual interference between channels and performing stable simultaneous measurement.

  According to the present invention, an oscillation circuit that incorporates a vibrator and obtains an oscillation operation is a grounded oscillation circuit that obtains an oscillation operation by grounding one electrode of the vibrator. Suppresses propagation and interference with other channels and enables stable simultaneous measurement, and has the following configuration.

(1) When a vibrator composed of a piezoelectric substrate and a vibrator electrode formed on the substrate surface is provided for a plurality of channels on one piezoelectric substrate, and one electrode of each vibrator is exposed to a sample gas or a sample solution In a multi-channel QCM sensor that detects and quantifies sample components from changes in the resonance frequency or impedance of each transducer
A plurality of oscillation circuits that oscillate using the vibrator of each channel as a resonance element are provided, and each oscillation circuit is configured as a grounded oscillation circuit in which one electrode of the vibrator is grounded. It is characterized by oscillating and detecting and quantifying sample components simultaneously for a plurality of channels.

  (2) Each vibrator is characterized in that an electrode exposed to a sample component is grounded and connected to a grounded oscillation circuit.

  (3) Among the plurality of channels, one channel is a measurement channel, one channel is a reference channel, and the difference between the oscillation frequency of the measurement channel and the oscillation frequency of the reference channel is detected as a sample component detection / quantification frequency signal. It is characterized by the configuration.

  (4) The oscillator is configured to oscillate by switching one oscillation circuit in time with respect to the plurality of vibrators.

  (5) The vibrator has a flow cell structure in which a sample component is allowed to flow on an electrode surface.

  As described above, according to the present invention, since an oscillation circuit that incorporates a vibrator and obtains an oscillation operation is a grounded oscillation circuit that obtains an oscillation operation by grounding one electrode of the vibrator, Simultaneously oscillates and suppresses electromagnetic waves from propagating to other channels and interfering with each other, enabling stable simultaneous measurement.

  Moreover, measurement accuracy can be improved by taking out one channel as a measurement channel and using one channel as a reference channel among a plurality of channels as a frequency change amount between channels.

  FIG. 1 is an oscillation circuit diagram applied to the multi-channel QCM sensor of the present invention, and shows an oscillation circuit for one channel.

  In the oscillation circuit shown in FIGS. 1A to 1C, TR is a transistor as an amplifying element, X is a crystal resonator, and an oscillation circuit is formed by these and circuit elements (resistance, capacitor, inductor). Then, an oscillation operation is obtained using the negative resistance of the crystal unit X.

  The crystal resonator X and the oscillating portion (a transistor as an amplifying element and a capacitor or an inductor as an impedance element) are integrally connected at the shortest distance. For example, the oscillation unit is formed on a printed circuit board, and the crystal unit X is attached to the surface of the printed circuit board.

  Furthermore, the oscillation circuit is configured as a grounded oscillation circuit that can ground one electrode of the crystal unit X. For example, in FIG. 1, among the external connection terminals of the crystal unit X, an external connection terminal connected to an electrode (solution exposed electrode surface) exposed to the sample solution is defined as a ground side terminal.

  By adopting such a grounded oscillation circuit, radiation / propagation of high frequency components from the ground side electrode and the connection line to the ground point is suppressed, and mutual interference between channels is suppressed. Thereby, even if each channel is oscillated continuously at the same time, stable oscillation and frequency measurement can be performed without being affected by the oscillation operation in each channel.

  Note that a float type oscillation circuit in which both electrodes of the crystal resonator are floated with respect to the ground type oscillation circuit shown in FIG. 1 has a circuit configuration shown in FIG. Since an alternating current component propagates between both electrodes of the child X, mutual interference occurs between the channels when immersed in a conductive solution such as an electrolytic solution.

  FIG. 3 shows an embodiment in which one channel is used as a reference channel in a QCM sensor having a two-channel configuration. The grounded oscillation circuit 1A to which the crystal resonator X1 is connected serves as a measurement channel, and the electrode of the crystal resonator X1 is exposed to the sample solution to obtain an oscillation output whose frequency is shifted by the sample component. The grounded oscillation circuit 1B to which the crystal resonator X2 is connected is used as a reference channel, and the electrode of the crystal resonator X2 is exposed to the sample solution. An oscillation output having an oscillation frequency when exposed to a solution is obtained.

  Both oscillation outputs of the grounded oscillation circuits 1A and 1B are detected by the heterodyne detector 2 so that the frequency difference between the reference channel and the measurement channel is a sample component detection / quantitative frequency signal. Thereby, highly accurate measurement which canceled the influence of the viscosity change of a solution, the pH change of a solution, etc. can be performed.

  In the above embodiments, a multi-channel QCM sensor using a crystal oscillator having a two-channel configuration and a grounded oscillation circuit is shown. However, a multi-channel QCM sensor configuration having four or nine channels is used to suppress mutual interference. Continuous simultaneous measurement is possible.

  Further, the configuration is not limited to a configuration in which an oscillation circuit is provided for each transducer, but a configuration in which one oscillation circuit is switched over time for a plurality of transducers, for example, a configuration in which four oscillation circuits are provided for an 8-channel configuration You can also.

The oscillation circuit diagram which shows embodiment of this invention. Float type oscillation circuit diagram. The block diagram of 2 channel QCM which shows other embodiment. Flow cell type multi-channel QCM sensor cell structure. The disassembled perspective view of a flow cell type multi-channel QCM sensor.

Explanation of symbols

X, X1, X2 Crystal resonator 1A, 1B Grounded oscillation circuit 2 Heterodyne detector

Claims (5)

Vibrators composed of a piezoelectric substrate and vibrator electrodes formed on the substrate surface are provided for a plurality of channels on one piezoelectric substrate, and each vibration when one electrode of each vibrator is exposed to a sample gas or a sample solution In a multi-channel QCM sensor that detects and quantifies sample components from changes in the resonance frequency or impedance of the child,
A plurality of oscillation circuits that oscillate using the vibrator of each channel as a resonance element are provided, and each oscillation circuit is configured as a grounded oscillation circuit in which one electrode of the vibrator is grounded. A multi-channel QCM sensor that oscillates and simultaneously detects and quantifies sample components for a plurality of channels.   2. The multichannel QCM sensor according to claim 1, wherein each of the vibrators is connected to a grounded oscillation circuit by grounding an electrode exposed to a sample component. 3.   Of the plurality of channels, one channel is a measurement channel, one channel is a reference channel, and the difference between the oscillation frequency of the measurement channel and the oscillation frequency of the reference channel is used as a sample component detection / quantification frequency signal. The multi-channel QCM sensor according to claim 1 or 2, characterized by the above.   3. The multi-channel QCM sensor according to claim 1, wherein the multi-channel QCM sensor is configured to oscillate by switching one oscillation circuit in time with respect to the plurality of vibrators.   The multi-channel QCM sensor according to claim 1, wherein the vibrator has a flow cell type structure in which a sample component is allowed to flow on an electrode surface.

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