JP2005134327A - Mass sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain the structure of a mass sensor element for accurately inspecting DNAs and improving the measurement precision of a piezoelectric single-crystal substrate. <P>SOLUTION: In the mass sensor having a holder for retaining the mass sensor which uses a piezoelectric single-crystal substrate for a substrate and the piezoelectric single-crystal substrate, where the mass sensor and the holder are integrated and the entire part is made of a piezoelectric single crystal, the mass sensor element section of the mass sensor is formed by a plate thickness that is thinner than the entire mass sensor, and holders for covering the thin part of at least the mass sensor element are laminated. <P>COPYRIGHT: (C)2005,JPO&NCIPI

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.
In a mass sensor using a piezoelectric single crystal as a sensor element, ng (nanogram) level weight measurement is possible. By immobilizing an antibody (or antigen) on the device surface, the antigen (or antibody) Detection is possible. In addition, regarding the PH value (the common logarithm of the reciprocal of the hydrogen ion concentration expressed in terms of molar concentration) and the conductivity, it is possible to detect a change in conductivity by an acoustoelectric interaction.

And since the process of reaction can be grasped as frequency change, real-time quantitative analysis becomes possible by measuring and recording the state of 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 the mass sensor shown in FIG. 6 captures a complementary binding reaction such as an antigen-antibody reaction or DNA-RNA binding, the mass sensor corresponds in advance to a reaction part of a 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 oppositely 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. This is a structure or cylinder in which a sensor element can be fixed with an epoxy-based adhesive at one end of a cylindrical holder made of a ceramic material that approximates the outer circumference of the sensor element, and the solution can be introduced into the cylinder. Is structured so as to be immersed in the liquid, and the opposite main surface is exposed in the gas phase.

  This structure can separate the gas phase and the liquid phase, but has a structure in which a piezoelectric single crystal substrate serving as a sensor element is attached to one bottom surface of the holder. In addition, because the mass sensor holder material is a ceramic material and the mass sensor element body is a piezoelectric single crystal substrate (quartz crystal material), it is a measurement that detects minute frequency changes as mass changes. This makes it difficult to measure changes in the state of the DNA sample.

  The present invention has been made to solve the above-described problems. A mass sensor using a piezoelectric single crystal substrate as a substrate and a mass sensor having a holder for holding the piezoelectric single crystal substrate. The holder is integrated and formed as a whole by a piezoelectric single crystal, and the mass sensor element portion of the mass sensor is formed with a plate thickness thinner than the entire mass sensor, and a holder that covers at least the thin portion of the mass sensor element is attached. The mass sensor is characterized in that the mass sensor is formed of a quartz crystal material that is a piezoelectric single crystal substrate.

  The above-described configuration of the mass sensor element improves the measurement accuracy for the analyte measurement, and simplifies the configuration of the mass sensor itself, thereby reducing the manufacturing man-hour and cost of the mass sensor element. Design freedom can be expanded.

  The present invention can accurately measure a minute change in DNA as a measurement object by significantly improving a distortion component with respect to a mass sensor element by configuring the entire mass sensor with a piezoelectric single crystal substrate. It has become possible. As a result, it was possible to greatly improve the degree of freedom of sample measurement and improve sample measurement workability.

  The QCM mass sensor that measures complementary binding reactions derived from biological systems, such as antigen-antibody reactions and DNA-DNA binding reactions, can be used for real-time quantitative analysis. Is also very important and has benefits. However, in the conventional mass sensor, the portion that holds the mass sensor element is formed of a material different from that of the mass sensor element. Therefore, when an accurate change measurement of the sensitive substance is attempted, the sensor element and its holding portion It is difficult to measure minute changes due to distortion components. In the present invention, the problems of the conventional mass sensor are solved, the measurement function as the mass sensor can be ensured accurately even with minute detection information, and the operability is simple and reliable and high-precision measurement is possible.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. The principle of operation of the mass sensor of the present invention shown in FIG. 1 is the same as that of the conventional mass sensor (the routing connection from the electrode is not particularly shown), and captures complementary binding reactions such as antigen-antibody reaction and DNA-RNA binding. In this case, when a sensitive substance such as a corresponding antigen, antibody, or DNA is added in advance to a reaction part of a sensor element (usually a metal electrode such as Au or Al) and immersed in a solution, two electrodes In the meantime, due to the occurrence of electrical leakage through the solution, it is unstable and connected with a finite impedance. It measures frequency changes due to mass changes that change depending on the state of reaction and bonding. Here, FIG. 1A is a perspective view and FIG. 1B is a cross-sectional view.

  FIG. 1 shows a main body portion of a mass sensor element. In a mass sensor using a piezoelectric single crystal substrate as a structure, the entire mass sensor is formed of a piezoelectric single crystal, and the mass sensor element portion is the mass sensor element. This is a mass sensor in which the mass sensor is formed of a quartz crystal material that is a piezoelectric single crystal substrate in a form that is thinner than the entire plate thickness. As an example of the outer dimensions, L = 50 mm and W = 10 to 20 mm.

  As shown in FIG. 2, the holder 4 is also formed of a piezoelectric single crystal substrate so as to sandwich the mass sensor element, and constitutes a mass sensor. When the entire mass sensor is formed of a piezoelectric single crystal substrate, the mass sensor element In order to easily vibrate, the mass sensor element portion of the mass sensor is formed with a plate thickness thinner than the entire mass sensor, and the mass sensor element 1 and the holder 4 It is also characterized by a form in which at least two of the above are laminated. In addition, it is effective that a structure for protecting the electrode routing of the mass sensor element can be adopted by arranging the piezoelectric single crystal substrate also above the mass sensor element drawn with a dotted line in the drawing of FIG. Here, FIG. 2A is a perspective view, FIG. 2B is a cross-sectional view, and the thickness of each substrate is drawn exaggerating the thickness.

  3A and 3B are a perspective view (FIG. 3A) and a cross-sectional view (FIG. 3B) of a crystal diaphragm showing an embodiment of the present invention. In the vibrator shown in this embodiment, the oscillation frequency is assumed to be 5 to 30 MHz, and the thickness of the mass sensor element 3 is 55 to 335 μm. The piezoelectric crystal substrate 1 is machined or chemically processed up to the above thickness. Processing is performed using processing (etching). Etching may be either dry etching or wet etching with a chemical solution.

  The size of the piezoelectric crystal substrate 1 is L = 50 mm, W = 10 to 20 mm, and the mass sensor element 3 that is a vibrating portion is not limited to the size of the piezoelectric crystal substrate 1 if it is smaller than the W dimension of the piezoelectric single crystal substrate 1. No. By processing the piezoelectric single crystal substrate 1 to form the mass sensor element 3, vibration leakage due to the adhesive is reduced, and high sensitivity, reliability of the device performance, and improvement in yield can be achieved.

  In the mass sensor element of the present invention, the metal electrode 2 faces the front and back of the main surface of the mass sensor element 3 in order to excite the fundamental wave of the thickness-shear vibration mode at the substantially central portion of the piezoelectric single crystal substrate constituting the element. Is formed. The metal electrode film is formed by depositing Ti, Ni, NiCr or the like as an adhesion film and Au or Al as an electrode material using an evaporation method or a sputtering method.

  Then, as shown in FIG. 3, the entire mass sensor is formed of a piezoelectric single crystal, and the mass sensor element is thinner than the entire thickness of the mass sensor. The mass sensor is made of a crystal material that is a piezoelectric single crystal substrate. Since it is a formed mass sensor, it represents a form in which the piezoelectric sensor is realized by bonding at least two piezoelectric single crystal substrates. It is assumed that the substrate (substrate constituting the mass sensor element 3) sandwiching the piezoelectric single crystal substrate forming the mass sensor is equal to or thinner than the thickness of the vibrating portion. In order to bond these substrates together, an insulating adhesive that does not affect the actual measurement is used.

  As described above, one mass sensor is configured by bonding at least two piezoelectric single crystal substrates of a flat plate forming a thin portion which is a vibrating portion of the mass sensor element and a portion forming the entire periphery thereof. is there. In this embodiment, the entire surface of the element is bonded to the holder, but it is sufficient to cover at least the element portion (thin portion) with the piezoelectric single crystal substrate.

As described above, DNA is adsorbed as a mass sensor element, and a lead electrode from the electrode of the mass sensor element necessary for realizing a mass sensor that measures a change in the state of the piezoelectric single crystal substrate with a frequency change in a solution is provided. If the configuration shown in FIG. 3 is adopted, the lead-out electrode can be sandwiched between two piezoelectric single crystal substrates, so that it can be used as a very powerful structure in a measurement method in which a mass sensor is immersed in a solution.
FIG. 4 shows a conceptual diagram of the measurement state of the mass sensor of the present invention. As can be seen from FIG. 4, a sample such as DNA is applied to the electrode portion 2 of the mass sensor element 3 and this portion is immersed in a solution to capture the change in the sample as a change in frequency.

  FIG. 5 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. 5 is placed in a thermostat that is precisely temperature controlled for the purpose of excluding the influence of temperature fluctuations, together with the oscillation circuit, and the solution used for the measurement also depends on 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 can be processed by a computer with a desired algorithm.

  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. It can measure a wide variety of sensitive substances.

It is a perspective view which shows an example of the mass sensor element of this invention. It is a perspective view which shows the structure of the mass sensor of this invention. It is the perspective view and sectional drawing explaining the conceptual diagram of the mass sensor of this invention. It is a conceptual diagram which shows the state of the sample measurement using the mass sensor 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

1 Piezoelectric single crystal substrate 2 Electrode 3 Mass sensor element 4 Holder

Claims (2)

In a mass sensor having a mass sensor element using a piezoelectric single crystal substrate as a substrate and a holder for holding the piezoelectric single crystal substrate,
The mass sensor and the holder are integrated and formed as a whole by a piezoelectric single crystal, the mass sensor element portion of the mass sensor is formed with a plate thickness thinner than the entire mass sensor, and at least the thin portion of the mass sensor element is formed A mass sensor characterized in that a covering holder is bonded. The mass sensor according to claim 1, wherein the mass sensor is a quartz material.

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