JP4158971B2 - Mass sensor - Google Patents

Description

  The present invention relates to a mass of QCM using “Sauerbrey's theory” that measures mass change by the magnitude of frequency change when various minute masses (objects) interposed on a piezoelectric single crystal substrate are attached. It relates to sensors.

  In recent years, research on global environmental pollution problems and human genetic elucidation has been conducted. For example, identification of environmental hormone species, antigen-antibody reaction, binding of high molecular proteins (DNA-DNA, DNA-RNA) Reactions, analysis of enzyme reactions, proteome analysis, etc. are actively performed. And as these analysis methods, apparatuses, such as a gas chromatography mass spectrometer (GC-MS), a high performance liquid chromatograph (HPLC), and a surface plasmon resonance measuring device (SPR), are used. These instruments are large and expensive equipment, and at the same time have a very high analytical sensitivity. However, pretreatment of the sample requires considerable labor and time, and it is difficult to analyze multiple components simultaneously. . In addition, there is always a demand to observe the reaction process in real time, but this is not possible with the above equipment.

When a complementary binding reaction such as an antigen-antibody reaction or DNA-RNA binding occurs, a change in weight or a change in dielectric constant occurs. With the QCM mass sensor, it is possible to capture such minute changes.
Mass sensors that use piezoelectric single crystals as sensor elements can measure ng-level weights, so antigens (or antibodies) can be detected by immobilizing antibodies (or antigens) on the device surface. It becomes. Further, regarding PH and conductivity, it is possible to detect a change in conductivity by an acoustoelectric interaction.

Since the reaction process can be understood as a frequency change, real-time quantitative analysis is possible by measuring and recording the state of the frequency change in real time.
JP-A-6-018394 JP 2001-153777 A JP-A-62-064934 (1) N. Miura, H. Higabashi, G. Sakai et al .: Piezoelectric crystal immunosensor for sensitive detection of methamphetamine (stimulant drug) in human urine Proc. Fourth Int. Meeting on Chemical Sensors, Technical Digest, Tokyo. Pp. 13- 17 (1992)

  When capturing a complementary binding reaction such as an antigen-antibody reaction or DNA-RNA binding, the mass sensor shown in FIG. 5 corresponds in advance on the reaction part of the sensor element (usually a metal electrode such as Au or Al). A sensitive substance such as an antigen, antibody, or DNA is added, and in this state, it is immersed in a solution while being excited at the natural vibration frequency by an oscillation circuit or the like, and changes depending on the reaction or binding state with the target substance. The frequency change due to the mass change is measured.

  At this time, the state of the natural vibration of the sensor element is “thickness shear vibration”, and in order to self-excited this vibration state, a metal electrode is required on the front and back of the main surface of the sensor element. Therefore, when immersed in a solution with this structure, an unstable circuit connected with a finite impedance is added between the two electrodes due to the occurrence of electrical leakage through the solution, and the oscillation frequency is Measurement becomes difficult due to instability.

As a countermeasure against this, it is conceivable that the opposite main surface that does not contribute to the reaction is subjected to an insulation treatment and immersed in a solution, but the excitation load becomes large and it is difficult to oscillate easily. Therefore, usually, the reaction main surface must be exposed in the solution, but the opposite main surface is exposed in the gas phase.
A structural example of a conventional mass sensor is shown in FIG. This is a structure in which the sensor element can be fixed with epoxy adhesive at one end of a cylindrical holder that approximates the outer circumference of the sensor element so that the opening is closed, and the solution can be introduced into the cylinder. Is exposed in the gas phase.

  This structure can separate the gas phase and the liquid phase, but since it is already fixed with an epoxy adhesive, it is difficult to add sensitive materials before measurement, problems that are limited, In order to cope with the downsizing, even if it is the sensor element peripheral portion, firmly fixing the portion where the propagation wave of the main vibration is not completely attenuated will significantly deteriorate the stability of vibration.

  The present invention has been made in order to solve the above-described problems, and since the holder and the mass sensor element are detachable, the holder and the mass sensor element are detachable because the holder is fixed by clamping and fitting. For this reason, after the sensitive material is attached only to the sensor element, it can be easily attached to the holder, and the sensitive material and the degree of freedom of the attachment work can be greatly expanded.

  In the present invention, since a sensitive substance can be added by a sensor element alone, handling is simple, and the degree of freedom and workability of the sensitive substance material are improved.

  The QCM mass sensor that measures complementary binding reactions derived from biological systems, such as antigen-antibody reactions and DNA-DNA binding reactions, can also perform real-time quantitative analysis and analyze the reaction form. In doing so, it is very important and has advantages. When many different types of sensitive substances are handled and analysis is attempted in a matrix, various types of sensitive substances are fixed on the reaction part of the sensor element (usually a metal electrode such as Au or Al) accordingly. There is a need. According to the present invention, in such a case, it is possible to perform processing with a single sensor element, and since the workability is simple and reliable, highly accurate measurement is possible.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. The operation principle of the mass sensor of the present invention shown in FIG. 1 is the same as that of the conventional mass sensor. When capturing a complementary binding reaction such as an antigen-antibody reaction or DNA-RNA binding, the reaction part of the sensor element (usually, When a corresponding antigen, antibody, or sensitive substance such as DNA is added on a metal electrode (Au, Al, etc.) and immersed in a solution, electrical leakage occurs between the two electrodes via the solution. The frequency due to the mass change that changes depending on the reaction with the target substance and the state of binding by immersion in the solution while being excited at the natural vibration frequency by an oscillation circuit etc. in an unstable and connected state with a finite impedance. It measures changes.

  Structurally, the entire mass sensor is composed of a holder and a mass sensor element, a holding part for holding the mass sensor element is formed in the holder, and the mass sensor element is structured to be detachable from the holder. It is a sensor. The material of the holder is formed using ceramic or the like.

  A specific structure is shown in FIG. 2 is a cross-sectional view (FIG. 2 (a)) and a perspective view (FIG. 2) of a mass sensor element 3 used in a mass sensor of the present invention in which electrodes 2 are formed on both main surfaces of a piezoelectric single crystal substrate 1. In FIG. (B)) is shown. The vibration mode of this element is “thickness shear vibration”, and the frequency is selected according to the viscosity and density of the solution. At this time, a method of changing the frequency of the fundamental wave or a method of changing the frequency by overtone vibration is used, and usually vibrations of several MHz to several tens of MHz are often used. FIG. 2A shows an example in which a sensitive substance is added to the metal electrode 2 immersed in the solution, and FIG. 2B shows an example in which the metal electrode 2 is formed on the sensor element. is there. Usually, the sensitive substance is formed by spin coating, vapor deposition, deposition, LB film formation or the like.

  FIG. 3 is a perspective view showing the characteristic part of the present invention as seen from the direction of arrow A in FIG. FIG. 1 shows that a mass sensor using a piezoelectric single crystal substrate is formed with a holder for holding the mass sensor element in the holder, and the mass sensor element is detachable from the holder. As for the main part which is the feature, the convex part protruding from the outer part of the mass sensor element and the concave part of the holder are fitted, and the convex part protruding from the outer part of the mass sensor element is electrically connected to the concave part of the holder. FIG. 3 shows that the mass sensor and the holder are integrated with each other by a conducting portion that conducts electricity.

  Further, although not shown in particular, when a holder in which the mass sensor element 3 is arranged on the upper part of the holder as shown in FIG. 3 is configured, one of the holders is closed so as not to leak the solution into the holder, and the mass sensor element 3 is arranged so as to float in the solution in the holder, the mass sensor element 3 can be held in the holder with an appropriate fit between the convex part 4 projecting to the outer shape part of the mass sensor element and the concave part 5 of the holder. it can. Therefore, there is a margin for slight movement.

And since the mass sensor element is in the fitting part with the holder, and the convex part protruding to the outer shape part of the mass sensor element is slightly movable in the concave part of the holder,
A corresponding antigen, antibody, or sensitive material such as DNA is added in advance to the reaction part of the sensor element (usually a metal electrode such as Au or Al), and in this state, the natural vibration frequency is generated by an oscillation circuit or the like. It is possible to simplify the holding and adjustment of a series of mass sensor elements when measuring a reaction with a target substance or a change in binding by immersing in a solution while being excited by the above.

  FIG. 4 is an example of a configuration diagram of an apparatus for measuring mass using the mass sensor of the present invention. The configuration shown in FIG. 4 is placed in a thermostat that is precisely temperature controlled for the purpose of eliminating the influence of temperature fluctuations for both oscillation circuits, and the solution used for the measurement is also subject to the temperature conditions of this thermostat. Managed. For frequency measurement, a frequency counter is used. As a reference of the counter, it is desirable to use a signal generated by an Rb oscillation and a highly stable crystal oscillator. Data obtained by the frequency counter has a structure that can be processed by a computer with a desired algorithm.

  As described in the embodiments of the present invention, the holder and the mass sensor element are detachable, and the piezoelectric single crystal substrate 1 is fixed by clamping and fitting in a detachable state to the holder part. Although not shown in particular, it goes without saying that a sealing structure is provided in the fixed portion of the piezoelectric single crystal substrate 1 so that the solution inside the holder does not leak out.

  This sensor has been described with respect to examples of measuring mass changes due to reactions and bonds in solution, but it is also effective for measurements in the gas phase, such as measuring the content of environmental pollutants such as dioxins. Easy processing of a wide variety of sensitive materials and the support of the sensor element can be fixed softly, so a very stable frequency can be obtained, enabling accurate measurement regardless of the gas phase or liquid phase. It becomes.

It is a conceptual diagram which shows an example of the liquid phase measurement mass sensor of this invention. It is the elements on larger scale which show the sensor element used for this invention. It is the elements on larger scale which paid its attention to the principal part which is the characteristics of this invention. It is a conceptual diagram which shows the structural example of the mass measuring device using the mass sensor element of this invention. It is a conceptual diagram which shows an example of the conventional liquid phase measurement mass sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piezoelectric single crystal substrate 2 Electrode 3 Mass sensor element 4 Convex part which protrudes in the external part of a mass sensor element

Claims (2)

In a mass sensor using a piezoelectric single crystal substrate, a holder is formed to hold the mass sensor element in a holder, and the mass sensor element is configured to be detachable from the holder . The convex portion protruding from the outer shape portion and the concave portion of the holder are fitted, and the convex portion protruding from the outer shape portion of the mass sensor element is connected to the concave portion of the holder by a conductive portion that is electrically connected to the sensor element. A mass sensor, wherein the holder and the holder are integrated. The mass sensor element according to claim 1 , wherein the convex portion protruding from the outer shape portion of the mass sensor element is slightly movable in the concave portion of the holder at the fitting portion with the holder. Mass sensor.

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