JP5224164B2 - Substance adsorption detection method and substance adsorption detection sensor - Google Patents

Description

  The present invention relates to a substance adsorption detection method using a piezoelectric element and a substance adsorption detection sensor. In particular, the present invention relates to a substance adsorption detection sensor and substance adsorption detection method using a quartz crystal microbalance and an optical waveguide.

As a conventional adsorption sensor, as disclosed in Patent Document 1, a small amount of NO ₂ gas is produced by utilizing the fact that the oscillation frequency of the crystal resonator is lowered according to NO ₂ gas adsorbed on the gas sensitive film. Sensors that can be detected are known.

  In addition, as disclosed in Patent Document 2, a method is known in which substance adsorption is detected by absorbing an evanescent field generated by guiding light through an optical waveguide by the adsorbed substance and attenuating the guided light. ing.

Further, as disclosed in Patent Document 3, a metal thin film is deposited on an optical waveguide, and when the surface plasmon is excited on the metal thin film by the guided light, the guided light is attenuated. In connection with this, there is known a method for detecting substance adsorption by measuring the emitted light using the change in the surface plasmon excitation condition.
JP 7-43285 A Japanese Patent Laid-Open No. 9-61346 JP 2001-108612 A

  However, in the conventional sensor disclosed in Patent Document 1 described above, it is possible to detect a very small amount of gas adsorbed on the gas-sensitive thin film by utilizing the nature of the crystal resonator, so-called QCM (Quartz Crystal Microbalance). This alone has the problem that the detection target substance and the optical properties of the sensitive thin film after adsorption cannot be directly known.

  Further, the conventional sensors disclosed in Patent Documents 2 and 3 have a problem in that it is impossible to directly know how much mass of the detection target substance is adsorbed on the element and causes a change in emitted light. It was.

  Accordingly, in view of the above problems, the present invention uses a substance adsorption detection sensor capable of accurately and simultaneously detecting the amount of change in the adsorption mass of a substance to be detected and the amount of change in the optical characteristics associated therewith using a piezoelectric element. An object of the present invention is to provide a method for detecting an adsorbed substance.

  In order to solve the above-mentioned problem, the substance adsorption detection method of the present invention comprises a quartz crystal part and electrodes formed on both sides of the quartz crystal part to constitute a quartz crystal oscillator, the oscillation characteristics of the crystal oscillator, and the quartz crystal In the substance adsorption detection method for measuring light guided by using a portion as an optical waveguide, one of the electrodes is also used as a metal thin film for surface plasmon resonance excitation.

  In this substance adsorption detection method, it is preferable to provide a sensitive material layer whose optical characteristics change due to substance adsorption on the one electrode side.

  Moreover, in this substance adsorption | suction detection method, you may measure the reference light and measurement light which guided the said crystal | crystallization part as an optical waveguide. In this case, it is preferable to determine the direction of the measurement light, that is, the propagation direction of light, which is the optical path of the measurement light, according to the optical axis direction.

  In order to solve the above-described problem, the substance adsorption detection sensor of the present invention includes a quartz crystal part and electrodes formed on both sides of the quartz crystal part. In a substance adsorption detection sensor for measuring light guided through a portion as an optical waveguide, one of the electrodes is also used as a metal thin film for surface plasmon resonance excitation.

  In this substance adsorption detection sensor, it is preferable to provide a sensitive material layer whose optical characteristics change due to substance adsorption on the one electrode side.

  Moreover, in this substance adsorption | suction detection sensor, you may measure the reference light and measurement light which guided the said crystal | crystallization part as an optical waveguide. A metal thin film that also serves as an electrode for surface plasmon resonance excitation is formed on the upper surface of the measurement light optical path, whereas an electrode for surface plasmon resonance excitation is formed on the upper surface of the optical path of the reference light. It is preferable that no metal thin film is formed. That is, with respect to the optical path of the measurement light, a metal thin film capable of surface plasmon resonance excitation is formed within the range where the evanescent wave of the measurement light is generated, and therefore surface plasmon resonance occurs efficiently. On the other hand, regarding the optical path of the reference light, the surface plasmon resonance does not occur efficiently because the metal thin film capable of exciting the surface plasmon resonance is not formed within the range where the evanescent wave of the measurement light is generated. Thus, the S / N ratio of the sensing sensitivity can be improved by comparing the intensities of the measurement light and the reference light.

  In addition, since the quartz substrate is a single crystal, it is different from the amorphous material such as glass used for the conventional surface plasmon resonance, and the substrate has optical anisotropy. It was difficult to obtain an appropriate surface plasmon resonance signal. Specifically, as will be described later, it is preferable to determine the direction of the measurement light in accordance with the optical axis direction. That is, since surface plasmon resonance is observed only in p-polarized light whose electric field oscillates perpendicular to the substrate, the surface parallel to the azimuth perpendicular to the substrate and the azimuth and the direction perpendicular to the optical path is It is preferable to set the optical path of the measuring light so that either the major axis or the minor axis of the refractive index ellipse, which is a cross section of the refractive index ellipsoid, is perpendicular to the substrate.

  An optical waveguide type surface plasmon resonance (SPR) sensor uses surface plasmon (SP) resonance by an evanescent wave in the vicinity of a waveguide core, and can perform highly sensitive sensing.

  The quartz crystal microbalance (QCM) method is also well known because it can detect a change in the adsorption mass of a substance with high sensitivity.

  In the present invention, one of the electrodes formed on both sides of the crystal part for performing QCM is also used as a metal thin film for surface plasmon (SP) resonance excitation, and light is guided through the crystal part, By using the SPR method and the QCM method in combination by performing SP excitation on the metal thin film that also serves as the electrode, a substance adsorption detection sensor capable of performing complex sensing, and this substance adsorption detection sensor were used. This is a substance adsorption detection method.

  According to the substance adsorption detection method and substance adsorption detection sensor according to the present invention, one of the electrodes formed on both sides of the crystal part for performing QCM is also used as a metal thin film for surface plasmon (SP) resonance excitation. Therefore, the surface plasmon can be resonantly excited in the metal thin film by the evanescent wave generated in the vicinity of the core by the guided light to the crystal part while reducing the number of parts and suppressing the cost. When surface plasmons are excited, the guided light attenuates, and the excitation conditions change sensitively due to the adsorption of the substance, so measuring the optical characteristics with higher sensitivity by measuring the emitted light, Oscillation characteristics can be observed. Furthermore, by depositing a sensitive material whose optical characteristics change due to substance adsorption on the surface of the metal thin film, it is possible to detect a trace amount of substance better.

  Of course, in the substance adsorption detection method and sensor of the present invention, as the substance to be detected is adsorbed on the surface of the optical waveguide, both the change in the emitted light due to the change in the propagation loss and the oscillation characteristics of the crystal resonator change. By utilizing this, it is possible to easily identify the substance to be detected. For example, when substances other than the detection target substance are adsorbed at the same time, it is impossible to identify only by the oscillation characteristics of the quartz crystal resonator in the sensor, but it is possible to simultaneously measure the refractive index by changing the optical characteristics. You can see that different media are adsorbed.

  The substance adsorption detection method and sensor according to the present invention is a piezoelectric element (quartz crystal resonator or surface acoustic wave element) having an optical waveguide, which can detect the adsorption mass of the substance by the piezoelectric element, and can output the substance adsorbed by the substance adsorption. The optical characteristics of the adsorbed substance or the thin film for detection after the substance adsorption can be observed with one element from the change of the incident light.

  Compared to the case where a piezoelectric element and an element for measuring optical characteristics are separately manufactured and observed, the above method can accurately detect the amount of change in adsorption mass and the amount of change in optical characteristic. In particular, when the adsorbed substance is decomposed by light irradiation, or when adsorption or desorption is promoted, a large error will occur if it is produced separately. It is possible to measure in detail the photodecomposition and the adsorption phenomenon by light.

  In addition, by observing the relationship between the adsorption mass and optical properties of several detection target substances, it is possible to identify substances with different masses that give the same change in optical properties per number of adsorbed molecules. It is.

  Hereinafter, preferred embodiments of the substance adsorption detection sensor of the present invention will be described with reference to the drawings. Note that, in each of these embodiments, the same portions are denoted by the same reference numerals, and the description of the common parts will be omitted as much as possible.

(Embodiment 1)
FIG. 1 is a cross-sectional view of a substance adsorption detection sensor 10 according to a preferred embodiment 1 of the present invention. It comprises a quartz crystal resonator 6 comprising a quartz crystal substrate 1 and a pair of quartz oscillation electrodes 2 and 3, and an adsorbed substance detection thin film (sensing layer) 4 disposed thereon. The sensing layer 4 is used as a gas adsorbing section, and bubbled vapor Vapor is introduced into a container containing a measurement target substance. Although an example using an AT-cut quartz substrate will be described here, it goes without saying that a quartz substrate cut in another orientation can be used in the present invention.

  The quartz substrate 1 is a quartz substrate in which the crystal cutting direction is AT cut. The crystal oscillation electrodes 2 and 3 are made of silver Ag (hereinafter referred to as Ag electrodes 2 and 3). The Ag electrodes 2 and 3 are formed on the quartz substrate 1 by vacuum deposition. Moreover, you may vapor-deposit through chromium and titanium.

  In FIG. 1, the thickness of the Ag electrode 2 formed below the quartz substrate 1 is 200 nm, and the thickness of the Ag electrode 3 formed above the quartz substrate 1 is 50 nm. The Ag electrode 3 is used not only as an electrode of the quartz substrate 1 but also as a metal thin film for resonantly exciting surface plasmons (SP) in this embodiment. That is, the Ag electrode 3 serves as the electrode of the quartz substrate 1 and the metal thin film for resonance excitation of the surface plasmon SP. A thickness of 50 nm is an optimum thickness for causing surface plasmon resonance. On the other hand, since the thickness of 200 nm is too thick to cause surface plasmon resonance, the thickness of the surface plasmon resonance is hardly obtained. The optimum thickness can be considered as in the case of surface plasmon resonance using a conventional prism. If it is too thick or too thin, the surface plasmon resonance signal is not observed sharply.

  Here, silver is adopted as the electrode substrate material that also serves as SPR, but it is needless to say that any metal exhibiting SPR may be used, and other metals can be used. For example, a gold electrode, a copper electrode, or the like can be employed depending on the purpose. In the case of silver, since the adhesiveness of the metal thin film to the quartz substrate is good, it is preferable from the viewpoint of durability. If a metal with poor adhesion is used, a thin film that does not affect the SPR, and a thin film for improving adhesion is used as a base, or the surface of the quartz substrate is roughened. It may be taken. As a thin film for improving adhesion, for example, nickel, chromium, titanium, platinum, or a composite film thereof can be used.

  The sensing layer 4 is formed by dip coating a polyvinyl alcohol (PVA) film on the side of the Ag electrode 3 having a thickness of 50 nm. The PVA concentration is 10 mg / ml, and the PVA film thickness is about 100 nm. Further, a base material 5 is formed of a PVA film on the Ag electrode 2 side.

  FIG. 2 is a top view of the substance adsorption detection sensor 10. The substance adsorption detection sensor 10 uses reference light (Reference Light) and measurement light (Signal Light) guided through a crystal part. The direction of the measurement light is determined according to the optical axis direction of the crystal portion. FIG. 2 shows the orientation flat surface facing down. The Ag electrode 3 shown in FIG. 1 is located on the orientation flat surface side. The Ag electrode 3 and the Ag electrode 2 are partially opposed to each other. When the white light introduced into the quartz substrate 1 passes under the Ag electrode 3, the surface plasmon SP is resonantly excited on the Ag electrode 3. And the light by which the surface plasmon SP was resonance-excited is radiate | emitted as a measurement light of an intensity | strength measuring object. The light that has passed over the Ag electrode 2 is emitted as reference light. The measurement light and the reference light are compared by a detector and a personal computer, which will be described later, and a change in the intensity of the measurement light affected by the SP resonance is detected.

  FIG. 3 is a diagram showing specific examples of dimensions of the quartz crystal substrate 1, the Ag electrode 2, and the Ag electrode 3. 2 has the orientation flat surface on the lower side and the incident end 1a on the left side when viewed from the paper surface, while FIG. 3 has the orientation flat surface on the upper side and the incidence end 1a on the right side. The length from the entrance end 1a to the exit end 1b of the quartz substrate 1 is, for example, 22.65 mm, and the widths of both Ag electrodes 2 and 3 are 8.0 mm.

  Here, the crystal orientation, incident light, and polarization direction of the quartz substrate 1 will be described. The light used in this embodiment is randomly polarized white light. Therefore, the generated surface plasmon resonance (SPR) measurement light (Signal Fight) is TM polarized light (p wave). The incident angle θ of light (angle measured from the substrate normal) may be made larger than the total reflection angle so as to satisfy the total reflection condition. In addition, since the propagation angle at which surface plasmon resonance occurs at a specific wavelength is specified, it is necessary to set appropriately according to the measurement wavelength range, the laminated film configuration of the quartz substrate, the metal thin film, and the sensing layer. When a monomolecular layer or the like is used as the sensing layer and the direction opposite to the metal thin film of the monomolecular layer is exposed to the gas layer, the angle is typically 20 ° to 40 °. When used in a liquid layer instead of a gas layer, the angle is 40 ° to 70 °. When an organic film that is somewhat thick is used as the sensing layer, the angle is typically 60 ° to 70 °.

  Next, with reference to FIGS. 4 to 6, the intensity change of the transmitted light depending on the incident position of the incident light on the quartz will be described. Here, Tama Device Co., Ltd. was used as the quartz substrate. Within the scope of the description of the present invention, the relationship between orientation flat and crystal orientation in a quartz substrate manufactured by Tama Device Co. is as described later. FIG. 4 shows the location of incidence on the crystal. The case where the incident location is the cut surface is [1], and the case where the incident point is a 90 ° point from the cut surface is [2]. FIG. 5A shows characteristics indicating the wavelength (horizontal axis) and outgoing light intensity (vertical axis) with respect to s (TE) polarized light incidence when the incident location is [1]. FIG. 5B also shows the characteristics indicating the wavelength (horizontal axis) and outgoing light intensity (vertical axis) for p (TM) polarized light incidence when the incident location is [1]. FIG. 6A shows the characteristics indicating the wavelength (horizontal axis) and outgoing light intensity (vertical axis) with respect to s-polarized light incidence when the incident location is [2]. FIG. 6B also shows the characteristics indicating the wavelength (horizontal axis) and outgoing light intensity (vertical axis) for p-polarized light incidence when the incident location is [2]. For light reception, regardless of whether the incident light is s or p, the light-receiving-side polarizing plate 0 ° is s-polarized light transmission. In this way, since the polarization plane rotates if the incident is inappropriate, the orientation of the orientation flat is used when using a crystal substrate such as the above crystal orientation in order to make the incidence from the direction where the polarization plane does not change. The incident angle is appropriately determined within an angle range close to. The angle is preferably about ± 10 ° with respect to the ideal crystal orientation. More preferably, the angle is ± 5 °. Most preferably, the angle is ± 1 °.

  The absorption spectrum of the light propagated through the waveguide before and after exposure to various solvent gases when white light is incident (IN) from one end face 1a of the quartz substrate 1 of the sensor configured as described above at an incident angle θ. Absorb. And the intensity | strength of the emitted light from the other end surface 1b is measured.

  As shown in FIGS. 1 to 3, when a 50 nm Ag electrode 3 is installed between the quartz substrate 1 and the sensing layer 4, the thickness and dielectric constant of the quartz substrate 1 and the Ag electrode 3, the thickness of the sensing layer 4, Surface plasmons can be excited on the Ag electrode 3 by an evanescent wave generated in the vicinity of the Ag electrode 3 for a certain wavelength and incident angle determined by the dielectric constant and the dielectric constant of the outside world. At this time, the transmitted light is attenuated at a wavelength for exciting the surface plasmon. By theoretically calculating the attenuation amount of the transmitted light, the dielectric constant or film thickness of the sensing layer 4 after adsorption of the substance to be detected is obtained, and the state of oscillation of the crystal resonator is detected. In this case, the sensing layer 4 and the substance to be detected are not necessarily light-absorbing. As described above, it is necessary to select the thickness of the metal thin film so that SPR occurs efficiently. In order to obtain the standard, the laminated film structure (the film thickness and dielectric constant of each layer, provided that the sensing layer is If it is thinner than the evanescent wave, it is necessary to consider the sensing environment).

  FIG. 7 is a configuration diagram of a substance adsorption detection system 20 using the substance adsorption detection sensor 10 shown in FIG. In the substance adsorption detection system 20, white light is incident on the quartz substrate 1 of the substance adsorption detection sensor 10 from a white light source 21.

  The white light IN incident on the quartz substrate 1 of the substance adsorption detection sensor 10 from the incident end IN propagates while being totally reflected, and is emitted OUT from the emitting end of the quartz substrate 1. The emitted light is detected by the detector 22. A detection signal from the detector 22 is processed by a personal computer (PC) 23 and displayed on the monitor 23a as a detection value or a change in characteristics.

  An oscillation controller 24 for supplying power to the Ag electrodes 2 and 3 and measuring the oscillation frequency is connected to the quartz substrate 1. The oscillation controller 24 is connected to the PC 23 and sends a signal indicating the oscillation frequency value to the PC 23.

  The PC 23 displays the intensity of the outgoing light transmitted from the quartz substrate 1 via the detector 22 on the monitor 23 a and also displays the QCM frequency sent from the quartz substrate 1 via the oscillation controller 24.

The sensing layer 4 of material suction detecting sensor 10 N ₂ gas was bubbled into a solution of dry N ₂ gas or object to be measured has flowed through the pipe 31 is supplied from the ejection port 31a. These gases, as a from the flow rate control pipe 26 a float meter N ₂ gas from the N ₂ gas cylinder (not shown), passes through the silica gel container 28 or solution container 29 via a valve 27, through valve 30 It is obtained by flowing in the pipe 31.

Dry N ₂ gas is obtained by adjusting the valve 27 and passing the N ₂ gas whose flow rate is adjusted from the float meter through the silica gel container 28. The valve 30 is opened and dry N ₂ gas is supplied to the sensing layer 4 from the jet port 31a through the pipe 31. On the other hand, N ₂ gas whose flow rate is adjusted from the float meter by adjusting the valve 27 is bubbled into the solution container 29 to obtain N ₂ gas containing moisture, ethanol, or acetone. The valve 30 is opened and moisture containing N ₂ gas, ethanol, or acetone is passed through the pipe 31 and introduced into the sensing layer 4 from the ejection port 31a.

Thus material suction detecting system 20, while switching dried N ₂ gas or solution to be measured through silica gel container 28, for example, pure water, ethanol, or the N ₂ gas was bubbled in as acetone valves 27 and 30 pipe 31, and is sprayed from the ejection port 31 a to the sensing layer 4 of the substance adsorption detection sensor 10. At that time, the intensity of the emitted light guided through the quartz substrate 1 and the oscillation frequency of the quartz substrate are simultaneously measured and measured by the PC 23. The result is processed and displayed on the monitor 23a.

Table 1 summarizes measurement condition examples when measurement is performed by the substance adsorption detection system 20 shown in FIG.

First, the measurement vapor is water vapor, ethanol vapor, or acetone vapor. The incident light to the quartz substrate is white light, and the incident angle θ is 60 ° to 70 °. The area of the Ag electrode 3 is 72.2 mm ² and the width of the Ag electrode is 8.0 mm. Moreover, the density | concentration of PVA used for the sensing layer 4 was 10 mg / ml with respect to the pure water, and the film thickness was formed in 100 nm by the dip coating method. Measurements were performed at room temperature. Of course, the measurement was performed in the substance adsorption detection system shown in FIG. 4 while exchanging the solution container 50 with an aqueous solution, an ethanol solution or an acetone solution.

  The measurement method is shown below. First, the sensing layer 4 of the sensor 10 is exposed to the substance to be detected, and a change in the oscillation frequency of the crystal substrate 1 is observed by the oscillation controller 24 and the PC 23 during that time. At the same time, white light is incident on the quartz substrate 1 from the white light source 21 at an incident angle θ = 60 ° to 70 ° to guide the quartz substrate 1. The incident angle θ of light is an angle within a range where light is totally reflected in the quartz substrate and light is guided. When white light is guided through the quartz substrate, an evanescent field is generated near the surface of the Ag electrode 3 (this distance is determined by the dielectric constant and the incident angle of the interface medium). If a metal thin film 3 such as gold, silver, or copper exists in a region where the evanescent field is generated, the evanescent field resonates with an SP (surface plasmon) wave generated in the metal thin film 3 and is absorbed by energy transfer. As a result, the light guided through the quartz substrate 1 is attenuated.

  That is, the sensing layer 4 is present in the area where the evanescent wave oozes, and if the dielectric constant of the sensing layer 4 that has adsorbed the substance to be detected changes before the adsorption, the SPR (surface of the evanescent wave by the metal thin film 3 is changed. Since the (plasmon resonance) absorption changes, the state of attenuation of the light OUT emitted from the emission end of the quartz substrate 1 also changes. The emitted light OUT is measured by the photodetector 22. Then, the measurement result is processed by the PC 23 and displayed on the monitor 23a. When the substance to be detected is adsorbed on the element and thus on the surface of the sensing layer 4, the spectrum or intensity of the light OUT emitted from the emission end of the quartz substrate 1 changes as described above. Usually, the angle scan is performed with a fixed wavelength (single wavelength), and the absorption under the SPR condition observed at a specific angle is measured. In the case of the present embodiment, the absorption under the SPR condition observed in a specific wavelength region is measured with white light (continuous wavelength) at a constant angle.

The following equation (1) indicates that the frequency changes depending on the absorbance on the metal electrode of the quartz substrate used in QCM (Quartz Crystal Microbalance). It is called the Sauerbrey equation and is an equation that defines the relationship between frequency and mass.

  By using this equation (1), it is possible to calculate the change Δm in the mass of the adsorbed material from the oscillation frequency change ΔF. Of course, equation (1) is also used in the following measurements.

(A), (B), and (C) of FIG. 8 are measurement results when water vapor is a measurement target. Water vapor (wetN ₂ ) had a humidity of 70%, and dry gas (dryN ₂ ) had a humidity of 15%. FIG. 8A shows light absorption spectrum (wavelength-absorbance) characteristics with the horizontal axis representing the wavelength of incident light and the vertical axis representing absorbance. FIG. 8B shows time-absorbance characteristics with the elapsed time on the horizontal axis and the absorbance on the vertical axis. This is a characteristic with respect to a wavelength of white light λ = 472 nm. FIG. 8C shows time-frequency change characteristics with the horizontal axis representing elapsed time and the vertical axis representing oscillation frequency change.

According to the light absorption spectrum characteristic shown in FIG. 8A, in the initial state (dry nitrogen gas N ₂ ), an absorption (absorbance) peak due to surface plasmon (SP) excitation is observed in the vicinity of 480 nm. However, it can be seen that the SP resonance changes due to moisture adsorption due to exposure of the sensing layer to water vapor (wet N ₂ ) gas for 15 minutes, and the absorbance peak shifts to the longer wavelength side. Next, when dry nitrogen gas N ₂ was introduced for 10 minutes, the absorbance almost returned to the initial state.

According to the time-absorbance characteristics shown in FIG. 8B, in the initial state (dry nitrogen gas N ₂ ), the absorbance is 0.3 and the sensing layer is exposed to water vapor (wet N ₂ ) gas for 15 minutes. It can be seen that the SP resonance changes due to moisture adsorption due to exposure, and the absorbance decreases to 0.18. Next, when dry nitrogen gas N ₂ was introduced for 10 minutes, the absorbance almost returned to the initial value.

According to the time-oscillation frequency change characteristic shown in FIG. 8C, in the initial state (dry nitrogen gas N ₂ ), the oscillation frequency change ΔF is 0, and the change to the water vapor (wet N ₂ ) gas for 15 minutes. It can be seen that the SP resonance changes due to humidity adsorption due to exposure of the sensing layer, and the oscillation frequency change ΔF changes to −160 Hz. Next, when dry nitrogen gas N ₂ was introduced for 10 minutes, the oscillation frequency change ΔF almost returned to the initial value.

As described above, the mass of this sensor increases by the amount of adsorption of the substance to be detected. The frequency decreases as the amount of gas to be detected increases. That is, the frequency characteristic of the crystal unit 6 changes in proportion to the mass of the adsorbed gas to be detected. In FIG. 8C, the H ₂ O mass was 2.02 μg when the oscillation frequency change ΔF was changed to −160 Hz.

Moreover, (A) and (B) of FIG. 9 are the repeated measurement results of water vapor introduction. FIG. 9A is a time-absorbance characteristic showing a change in absorbance with respect to elapsed time. In particular, the time change of absorbance at a wavelength of 472 nm is shown. FIG. 9B shows time-oscillation frequency characteristics indicating changes in oscillation frequency with respect to elapsed time. In both cases, the introduction of dry N ₂ gas and water vapor N ₂ gas was repeated for 5 minutes. Both the change in absorbance and the change in oscillation frequency decreased when water vapor gas was introduced, and reversibility was restored to the initial state when dry gas was introduced.

  From the above, when water vapor was sensed by the substance adsorption detection system 20, it was observed that the absorbance peak was due to surface plasmon excitation. It was also observed that the absorbance peak was shifted by water vapor gas adsorption. In addition, the light absorption spectrum and the oscillation frequency change could be observed reversibly in the cycle of initial state, water vapor gas introduction, and dry gas introduction.

  Therefore, it has been found that the substance adsorption detection sensor 10 according to the present embodiment, which is a composite of surface prosmon resonance and QCM, enables mass sensing with high sensitivity to water vapor.

  (A), (B), and (C) of FIG. 10 are measurement results when ethanol vapor is the measurement object. FIG. 10A shows a light absorption spectrum (wavelength-absorbance) characteristic with the horizontal axis representing the wavelength of incident light and the vertical axis representing absorbance. FIG. 10B shows time-absorbance characteristics with the elapsed time on the horizontal axis and the absorbance on the vertical axis. FIG. 10C shows time-frequency change characteristics with the horizontal axis representing elapsed time and the vertical axis representing oscillation frequency change.

According to the light absorption spectrum characteristic shown in FIG. 10A, in the initial state (dry nitrogen gas N ₂ ), an absorption (absorbance) peak due to surface plasmon (SP) excitation is seen in the vicinity of 480 nm. However, it can be seen that the SP resonance changed due to humidity adsorption due to exposure of the sensing layer to ethanol vapor for 15 minutes, and the absorbance peak shifted to the longer wavelength side. Next, when dry nitrogen gas N ₂ was introduced for 10 minutes, the absorbance almost returned to the initial state.

According to the time-absorbance characteristics shown in FIG. 10 (B), in the initial state (dry nitrogen gas N ₂ ), the absorbance is 0.3, and humidity adsorption due to exposure of the sensing layer to ethanol vapor for 15 minutes. It can be seen that the SP resonance has changed and the absorbance has decreased to 0.23. Next, when dry nitrogen gas N ₂ was introduced for 10 minutes, the absorbance almost returned to the initial value.

According to the time-oscillation frequency change characteristic shown in FIG. 10C, in the initial state (dry nitrogen gas N ₂ ), the oscillation frequency change ΔF is 0, which is due to exposure of the sensing layer to ethanol vapor for 15 minutes. It can be seen that the SP resonance changes due to moisture adsorption, and the oscillation frequency change ΔF changes to −61 Hz. Next, when dry nitrogen gas N ₂ was introduced for 10 minutes, the oscillation frequency change ΔF almost returned to the initial value.

  As described above, the mass of this sensor increases by the amount of adsorption of the substance to be detected. The frequency decreases as the amount of gas to be detected increases. That is, the frequency characteristic of the crystal unit 6 changes in proportion to the mass of the adsorbed gas to be detected. In FIG. 10C, the ethanol mass was 0.77 μg when the oscillation frequency change ΔF was changed to −61 Hz.

Moreover, (A) and (B) of FIG. 11 are the repeated measurement results of ethanol vapor introduction. FIG. 11A is a time-absorbance characteristic showing a change in absorbance with respect to elapsed time. In particular, the time change of absorbance at a wavelength of 472 nm is shown. FIG. 11B is a time-oscillation frequency characteristic showing an oscillation frequency change with respect to the elapsed time. In both cases, the introduction of dry N ₂ gas and ethanol vapor was repeated for 5 minutes. Both the change in absorbance and the change in oscillation frequency decreased when ethanol vapor was introduced, and reversibility was restored to the initial state when dry gas was introduced.

  From the above, when ethanol was sensed by the substance adsorption detection system 20, it was observed that the absorbance peak was due to surface plasmon excitation. It was also observed that the absorbance peak was shifted by ethanol adsorption. In addition, the light absorption spectrum and the oscillation frequency change were reversibly observed in the cycle of initial state, ethanol vapor introduction, and dry gas introduction.

  Therefore, it has been found that the substance adsorption detection sensor 10 of the present embodiment, which is a composite of surface prosmon resonance and QCM, enables highly sensitive mass sensing with respect to ethanol vapor.

  (A), (B), and (C) of FIG. 12 are measurement results when acetone vapor is the measurement target. FIG. 12A shows a light absorption spectrum (wavelength-absorbance) characteristic with the horizontal axis representing the wavelength of incident light and the vertical axis representing absorbance. FIG. 12B shows time-absorbance characteristics with the elapsed time on the horizontal axis and the absorbance on the vertical axis. FIG. 12C shows time-frequency change characteristics with the horizontal axis representing elapsed time and the vertical axis representing oscillation frequency change.

According to the light absorption spectrum characteristic shown in FIG. 12A, in the initial state (dry nitrogen gas N ₂ ), an absorption (absorbance) peak due to surface plasmon (SP) excitation is seen in the vicinity of 490 nm. However, it can be seen that the SP resonance changes due to humidity adsorption by exposure of the sensing layer to acetone vapor for 15 minutes, and the absorbance peak shifts to the longer wavelength side. Next, when dry nitrogen gas N ₂ was introduced for 10 minutes, the absorbance almost returned to the initial state.

According to the time-absorbance characteristics shown in FIG. 12 (B), in the initial state (dry nitrogen gas N ₂ ), the absorbance is 0.3, and humidity adsorption due to exposure of the sensing layer to ethanol vapor for 15 minutes. It can be seen that the SP resonance has changed and the absorbance has decreased to 0.26. Next, when dry nitrogen gas N ₂ was introduced for 10 minutes, the absorbance almost returned to the initial value.

According to the time-oscillation frequency change characteristic shown in FIG. 12C, in the initial state (dry nitrogen gas N ₂ ), the oscillation frequency change ΔF is 0, which is due to exposure of the sensing layer to acetone vapor for 15 minutes. It can be seen that the SP resonance changes due to moisture adsorption, and the oscillation frequency change ΔF changes to −58 Hz. Next, when dry nitrogen gas N ₂ was introduced for 10 minutes, the oscillation frequency change ΔF increased but did not reach the initial value.

  As described above, the mass of this sensor increases by the amount of adsorption of the substance to be detected. The frequency decreases as the amount of gas to be detected increases. That is, the frequency characteristic of the crystal unit 11 changes in proportion to the mass of the detected gas that has been adsorbed. In FIG. 12C, the acetone mass was 0.74 μg when the oscillation frequency change ΔF was changed to −58 Hz.

Moreover, (A) and (B) of FIG. 13 are repeated measurement results of acetone vapor introduction. FIG. 13A is a time-absorbance characteristic showing a change in absorbance with respect to elapsed time. In particular, the time change of absorbance at a wavelength of 472 nm is shown. FIG. 13B shows a time-oscillation frequency characteristic indicating a change in oscillation frequency with respect to elapsed time. In both cases, the introduction of dry N ₂ gas and acetone vapor was repeated for 5 minutes. Both the change in absorbance and the change in oscillation frequency decreased when acetone vapor was introduced, and reversibility increased when dry gas was introduced.

  From the above, when acetone was sensed by the substance adsorption detection system 20, it was observed that the absorbance peak was due to surface plasmon excitation. It was also observed that the absorbance peak was shifted by acetone adsorption. In addition, the light absorption spectrum and the oscillation frequency change were reversibly observed in the cycle of initial state, acetone vapor introduction, and dry gas introduction.

  Therefore, it has been found that the substance adsorption detection sensor according to the present embodiment, which is a composite of surface prosmon resonance and QCM, enables mass sensing even for acetone vapor.

  According to the above configuration, the surface plasmon can be resonantly excited in the Ag electrode 3 by the evanescent wave generated in the quartz crystal by the guided light by using the Ag electrode of the crystal resonator as the metal thin film.

  When surface plasmons are excited, the guided light attenuates, and the excitation conditions change sensitively due to the adsorption of the substance. Therefore, while measuring optical characteristics with higher sensitivity by measuring the emitted light, crystal oscillation The oscillation characteristics of the child can be observed.

Furthermore, by depositing a sensitive material whose optical characteristics change as a result of substance adsorption on the surface of the Ag electrode 3 as the sensing layer 4, it is possible to detect a trace amount of substance better.
Of course, since the substance adsorption detection sensor shares the Ag electrode and the metal thin film, the number of parts can be reduced. In addition, costs can be reduced.

  In the above embodiments, the substance adsorption detection sensor may be in gas or liquid.

  In addition, this invention is not limited to the said Embodiment 1, It can change in the range which does not deviate from the meaning of this invention. As the crystal oscillation electrodes 2 and 3, silver Ag is used, but gold and copper can also be used. The shape of the sensing layer 4 is not particularly limited, and various substances can be detected by changing the material. Further, the shape of the crystal oscillation electrode is not limited to the first embodiment, and may be a shape as shown in the following second embodiment, for example.

(Embodiment 2)
FIG. 14 is a top view of the substance adsorption detection sensor 40 according to a preferred embodiment 2 of the present invention, and shows the orientation flat surface below the paper surface. The substance adsorption detection sensor 40 also uses reference light and measurement light guided through a crystal part. The Ag electrode 43 and the Ag electrode 42 are partially opposed to each other. When white light introduced from the incident end 41 a into the quartz substrate 41 passes under the Ag electrode 43, the surface plasmon SP is resonantly excited on the Ag electrode 43. And the light by which the surface plasmon SP was resonance-excited is radiate | emitted from the output end 41b as measurement light of an intensity | strength measuring object.

  In the substance adsorption detection sensor 40 of the second embodiment, the shapes of the Ag electrode 42 and the Ag electrode 43 are different from the shapes of the Ag electrode 2 and the Ag electrode 3 of the first embodiment. The Ag electrode 43 is formed wide with a measuring light passing portion having a width of 8.0 mm. The second embodiment is different from the first embodiment in the electrode structure. As shown in FIG. 14, the electrode serving as the SPR thin film on the front side and the electrode on the back side are taken out from the same direction.

  In the structure of FIG. 2, since the difference between the reference light and the measurement light is only the presence or absence of the surface electrode, it is possible to detect only the contribution of the light intensity change by the electrode that also serves as the SPR thin film on the SPR surface side. On the other hand, in the second embodiment, the passage of the reference light is not affected by the absorption effect of the back side electrode. Therefore, even if the intensity of the reference light is reduced, sufficient reference light is obtained. Since the amount of light can be obtained, it is advantageous in terms of power consumption. You can use them according to your purpose.

  The substance adsorption detection sensor 40 of the second embodiment can also be used in the substance adsorption detection system shown in FIG. When white light is guided through the quartz substrate, an evanescent field is generated near the surface of the Ag electrode 43 (this distance is determined by the dielectric constant and incident angle of the interface medium). If a metal thin film 43 such as gold, silver, or copper is present in a region where the evanescent field is generated, the evanescent field resonates with an SP (surface plasmon) wave generated in the metal thin film 43 and is absorbed by energy transfer. As a result, the light guided through the quartz substrate 1 is attenuated.

  That is, the sensing layer 4 is present in the area where the evanescent wave oozes, and the SPR (surface plasmon) of the evanescent wave caused by the metal thin film 43 changes when the dielectric constant of the sensing layer that adsorbs the substance to be detected changes before the adsorption. Since the (resonance) absorption changes, the attenuation of the light OUT emitted from the emission end 41b of the quartz substrate 41 also changes. The emitted light OUT is measured by the photodetector 22. Then, the measurement result is processed by the PC 23 and displayed on the monitor 23a. When the substance to be detected is adsorbed on the element and thus on the sensing layer surface, the spectrum or intensity of the light OUT emitted from the emission end 41b of the quartz substrate 41 changes as described above.

Hereinafter, the results of measurement performed by applying three examples embodying Embodiment 2 of the present invention to the system of FIG. 7 will be described. Table 2 is a table showing measurement conditions.

(Definition of three examples)
The measurement steam was pure water. The incident angle θ of white light introduced into the quartz substrate is 65 °. Further, the electrode area of the upper Ag electrode 43 was 70.2 mm ^2, and the electrode width of the wide portion through which the measurement light passes was 8.0 mm. The number of reflections at the Ag electrode 43 (upper side) was set to six. And the PVA density | concentration for forming a sensing layer was set to three of 10, 20, and 30 mg / ml. Since the sensing layer is formed by dip-coating a crystal resonator on a PVA solution, the thickness of the sensing layer can be made different by varying the PVA concentration. The measurement was performed at room temperature.

Table 3 shows the PVA concentration, PVA film thickness, and absorption peak wavelength of Examples 1, 2 and 3. In Example 1, the PVA concentration was 10 mg / ml, and the PVA film thickness was 60 nm. The absorption peak wavelength measured was 440 nm. In Example 2, the PVA concentration was 20 mg / ml, and the PVA film thickness was 177 nm. The absorption peak wavelength measured was 528 nm. In Example 3, the PVA concentration was 30 mg / ml, and the PVA film thickness was 599 nm. The absorption peak wavelength measured was 752 nm.

(Absorption peak wavelength of three examples)
FIG. 15 shows the absorbance spectrum characteristics of Example 1 <1>, Example 2 <2>, and Example 3 <3>. The horizontal axis represents wavelength and the vertical axis represents absorbance. In Example 1 <1>, the absorption peak wavelength was 440 nm as described above. In Example 2 <2>, it was 528 nm as described above, and in Example 3 <3>, it was 752 nm. Therefore, it can be seen that as the thickness of the sensing layer increases, the absorption peak wavelength increases and the level also decreases.

  When the sensing layer has a constant dielectric constant, the peak wavelength of the absorption spectrum shifts to the longer wavelength side as the thickness of the sensing layer increases. In the case of the same film thickness, the peak wavelength of the absorption spectrum shifts to the longer wavelength side as the dielectric constant of the sensing layer increases. In this example, a PVA thin film was formed as the sensing layer. The film thickness could be increased by increasing the concentration of PVA. The film thickness of PVA was calculated from the amount of change in frequency of QCM. Thus, one of the advantages of the composite sensor substrate of the present invention is that the thickness of the sensing layer can be accurately measured by changing the frequency of the QCM. By appropriately selecting the thickness of the sensing layer, the absorption peak wavelength can be designed at a desired position. In this way, the sensor structure can be optimized so as to have the highest sensitivity in monochromatic measurement at a specific wavelength.

(Details of measurement results of Example 1)
Next, the details of the measurement results when water vapor is the measurement target in the substance adsorption detection sensor of Example 1 will be described. Water vapor (wetN ₂ ) had a humidity of 70%, and dry gas (dryN ₂ ) had a humidity of 15%. FIG. 16A shows light absorption spectrum (wavelength-absorbance) characteristics with the horizontal axis representing the wavelength of incident light and the vertical axis representing absorbance. FIG. 16B shows time-absorbance characteristics with the elapsed time on the horizontal axis and the absorbance on the vertical axis. This is a characteristic with respect to a wavelength of white light λ = 440 nm. FIG. 16C shows time-frequency change characteristics with the elapsed time as the horizontal axis and the oscillation frequency change ΔF as the vertical axis.

According to the light absorption spectrum characteristic shown in FIG. 16A, in the initial state (dry nitrogen gas N ₂ ), an absorption (absorbance) peak due to surface plasmon (SP) excitation is seen near 440 nm. However, it can be seen that the SP resonance changes due to moisture adsorption due to exposure of the sensing layer to water vapor (wet N ₂ ) gas for 15 minutes, and the absorbance peak is shifted to the long wavelength side by about 15 nm. Next, when dry nitrogen gas N ₂ was introduced for 10 minutes, the absorbance almost returned to the initial state.

According to the time-absorbance characteristics shown in FIG. 16B, in the initial state (dry nitrogen gas N ₂ ), the absorbance is 0.3 and the sensing layer is exposed to water vapor (wet N ₂ ) gas for 15 minutes. It can be seen that the SP resonance changes due to moisture adsorption due to exposure, and the absorbance decreases to 0.24. Next, when dry nitrogen gas N ₂ was introduced for 10 minutes, the absorbance almost returned to the initial value.

According to the time-oscillation frequency change characteristic shown in FIG. 16C, in the initial state (dry nitrogen gas N ₂ ), the oscillation frequency change ΔF is 0, and the change to the water vapor (wet N ₂ ) gas for 15 minutes. It can be seen that the SP resonance changes due to humidity adsorption due to exposure of the sensing layer, and the oscillation frequency change ΔF changes to −65 Hz. Next, when dry nitrogen gas N ₂ was introduced for 10 minutes, the oscillation frequency change ΔF almost returned to the initial value.

  Due to moisture absorption, the peak wavelength of the absorption spectrum shifted to the longer wavelength side by 15 nm. The frequency change of the QCM signal measured simultaneously was −70 Hz, and the amount of water molecules adsorbed was estimated to be 0.88 μg.

(Details of measurement results of Example 2)
Water vapor (wetN ₂ ) had a humidity of 70%, and dry gas (dryN ₂ ) had a humidity of 15%. FIG. 17A shows the light absorption spectrum (wavelength-absorbance) characteristics. FIG. 17B shows time-absorbance characteristics. This is a characteristic with respect to a wavelength of white light λ = 528 nm. FIG. 17C shows time-frequency change characteristics.

According to the light absorption spectrum characteristic shown in FIG. 17A, in the initial state (dry nitrogen gas N ₂ ), an absorption (absorbance) peak due to SP excitation is seen in the vicinity of 528 nm. It can be seen that the SP resonance changes due to moisture adsorption due to exposure of the sensing layer to the wet N ₂ ) gas, and the absorbance peak is shifted by about 20 nm to the longer wavelength side. Next, when dry nitrogen gas N ₂ was introduced for 10 minutes, the absorbance almost returned to the initial state.

According to the time-absorbance characteristics shown in FIG. 17B, in the initial state (dry nitrogen gas N ₂ ), the absorbance is 0.3 and the sensing layer is exposed to water vapor (wet N ₂ ) gas for 15 minutes. It can be seen that the SP resonance was changed by moisture adsorption due to exposure, and the absorbance decreased to 0.20. Next, when dry nitrogen gas N ₂ was introduced for 10 minutes, the absorbance almost returned to the initial value.

According to the time-oscillation frequency change characteristic shown in FIG. 17C, in the initial state (dry nitrogen gas N ₂ ), the oscillation frequency change ΔF is 0, and the change to the water vapor (wet N ₂ ) gas for 15 minutes. It can be seen that the SP resonance changes due to humidity adsorption due to exposure of the sensing layer, and the oscillation frequency change ΔF changes to −120 Hz. Next, when dry nitrogen gas N ₂ was introduced for 10 minutes, the oscillation frequency change ΔF almost returned to the initial value.

  Due to moisture absorption, the peak wavelength of the absorption spectrum shifted to the longer wavelength side by 20 nm. The frequency change of the QCM signal measured at the same time was −123 Hz, and the water molecule adsorption amount was estimated to be 1.55 μg.

(Details of measurement results of Example 3)
Water vapor (wetN ₂ ) had a humidity of 70%, and dry gas (dryN ₂ ) had a humidity of 15%. FIG. 18A shows a light absorption spectrum (wavelength-absorbance) characteristic. FIG. 18B shows time-absorbance characteristics. This is a characteristic with respect to the wavelength of white light λ = 752 nm. FIG. 18C shows time-frequency change characteristics.

According to the light absorption spectrum characteristic shown in FIG. 18A, in the initial state (dry nitrogen gas N ₂ ), an absorption (absorbance) peak due to SP excitation is seen in the vicinity of 752 nm. It can be seen that the SP resonance changes due to moisture adsorption due to exposure of the sensing layer to the wet N ₂ ) gas, and the absorbance peak is shifted to the long wavelength side by about 28 nm. Next, when dry nitrogen gas N ₂ was introduced for 10 minutes, the absorbance almost returned to the initial state.

According to the time-absorbance characteristics shown in FIG. 18B, in the initial state (dry nitrogen gas N ₂ ), the absorbance is 0.2 and the sensing layer is exposed to water vapor (wet N ₂ ) gas for 15 minutes. It can be seen that the SP resonance changes due to moisture adsorption due to exposure, and the absorbance decreases to 0.15. Next, when dry nitrogen gas N ₂ was introduced for 10 minutes, the absorbance almost returned to the initial value.

According to the time-oscillation frequency change characteristic shown in FIG. 18C, in the initial state (dry nitrogen gas N ₂ ), the oscillation frequency change ΔF is 0, and the change to the water vapor (wet N ₂ ) gas for 15 minutes. It can be seen that the SP resonance changes due to humidity adsorption due to exposure of the sensing layer, and the oscillation frequency change ΔF changes to −320 Hz. Next, when dry nitrogen gas N ₂ was introduced for 10 minutes, the oscillation frequency change ΔF almost returned to the initial value.

  Due to moisture absorption, the peak wavelength of the absorption spectrum shifted to the 28 nm short wavelength side. The frequency change of the QCM signal measured simultaneously was −328 Hz, and the amount of water molecules adsorbed was estimated to be 4.14 μg.

(Comparison of measurement results of three examples)
Examples 1, 2, and 3 differ in the thickness of the sensing layer. The film thickness of Example 1 was 60 nm, that of Example 2 was 177 nm, and that of Example 3 was 599 nm. The shift to the long wavelength side of the absorbance peak is 15 nm in Example 1, 20 nm in Example 2, and 28 nm in Example 3. Therefore, as the film thickness increases, the shift to the long wavelength side of the absorbance peak increases. It became long. Further, the oscillation frequency change ΔF due to the exposure of the sensing layer to water vapor (wet N ₂ ) gas is −65 Hz in Example 1, −120 Hz in Example 2, and −320 Hz in Example 3, and thus the film thickness is large. As the result, the oscillation frequency change ΔF becomes higher.

  In Embodiments 1 and 2, and Examples 1 to 3, an AT-cut quartz substrate was used as the quartz substrate. Hereinafter, the relationship between the plane orientation of the AT-cut quartz substrate and the orientation flat will be described in detail.

  In order to investigate the relationship between the crystal orientation of the quartz substrate and the light propagation direction, an X-ray cut surface inspection was performed. As an X-ray source, a CuKα target was used, and measurement was performed under conditions of 50 kV and 200 mA. The measurement resolution is 1/1000 °. The measurement lattice plane to be measured is (011). In an ideal AT-cut crystal, as shown in FIG. 19B, the angle between the surface normal and the Z axis is 51 ° 47 ′ ( The inclination angle of the surface is 38 ° 13 ′), the angle formed with the Z axis of the AT cut surface is 35 ° 15 ′, and the difference from the surface normal is 2 ° 58 ′. As for the measurement results of the cut surface inspection, all the quartz substrates were AT cuts, and the error of crystal orientation was within 0.3 °.

  It was also found that the quartz X-axis and the orientation direction of the orientation flat differ depending on the quartz substrate manufacturer. The orientation of the quartz made by MAXTEK in FIG. 20A was found to be arranged parallel to the X axis of the quartz and the side direction of the orientation flat. On the other hand, it was found that the orientation of the quartz manufactured by Tama Device Co. in FIGS. 20B and 20C was perpendicular to the X axis of the quartz and the side direction of the orientation flat. That is, the relationship between the orientation flat direction and the crystal X-axis direction may differ by 90 ° depending on the manufacturer.

  In the experiment of the present invention, an AT-cut quartz substrate manufactured by Tama Device Co., Ltd. is mainly used, and the crystal orientation of the quartz and the orientation flat are in the relationship of FIG. 20 (B) or (C).

  The propagation direction of light as the optical waveguide of the present invention should be understood in relation to such a crystal orientation, and should be used while paying attention to the correspondence relationship with the orientation flat direction of the substrate.

  19A and 19B show the relationship between the crystal direction and the cut surface (orientation flat and cut-out plate surface). FIG. X,. Y,. Z represents the coordinates on the cut surface cut out of the substrate. FIG. 19B shows crystal orientations (crystal axes) of quartz with X, Y, and Z. The angle θ1 is. The angle between the (011) plane normal line AX of the quartz substrate and the Z axis is shown. The angle θ2 is. The angle between Z and the Z axis is shown. The x-axis is perpendicular to the orientation flat surface, and. y is parallel to the orientation flat surface. In the present invention, the direction of the measurement light is determined according to the optical axis direction.

  It is preferable to arrange the optical path in the direction in which the surface normal created by the incident light and the outgoing light coincides with the optical axis in the quartz substrate. In order to obtain a clear SPR signal, it is necessary to select the light propagation direction so that the TE and TM polarized waves coincide with the optical axis of the quartz substrate in the propagation direction as an optical waveguide. Effective to get. That is, it is only necessary to select an orientation in which the major axis and the minor axis of the ellipse in the cross section of the refractive index ellipsoid on the vertical plane of the light propagation direction are perpendicular to the crystal substrate surface and horizontal or vice versa.

  (A), (B) and (C) in FIG. 20 also show the relationship between the crystal direction and the cut surface (orientation flat and cut-out plate surface), and three types of substrates (A) and (B) from different manufacturers. , (C) as an example, it is shown that there are a pattern (A) whose X-axis is parallel to the orientation flat, and a vertical pattern (B), (C). In this drawing, X, Y, and Z indicate crystal orientations (crystal axes) of quartz. X,. Y,. Z represents the coordinates on the cut surface cut out of the substrate.

  21 and 22 show the refractive index measurement results for a substrate having a pattern in which the X axis is perpendicular to the orientation flat.

  The refractive index was evaluated by measuring the critical angle with a prism made by GGG at a measurement wavelength (HeNe) of 632.8 nm using a prism coupler 2010 manufactured by Metricon. The relationship between the propagation direction and the refractive index ellipsoid in the quartz substrate of each company is shown together in FIG. The axis ratio of the ellipsoid is highlighted for easy understanding. 21 to 22 show the measurement results in the case of quartz manufactured by Tama Device Co., but in the case of quartz manufactured by MAXTEK Co., as described with reference to FIGS. It became a relationship. That is, in the crystal manufactured by Tama Device Co., when the light is guided in parallel with the orientation flat, the TE / TM polarization plane coincides with the optical axis (see FIG. 21B), but the polarization plane does not rotate, but is perpendicular to the orientation flat. When guided, the TE / TM polarization plane does not coincide with the optical axis (see FIG. 22B), so the polarization plane rotates. On the other hand, in the quartz made by MAXTEK, on the other hand, when the wave is guided in parallel with the orientation flat, the polarization plane of TE · TM does not coincide with the optical axis, so the polarization plane rotates. -Since the polarization plane of TM coincides with the optical axis, the polarization plane does not rotate. Therefore, in order to properly operate the sensor of the present invention, it is preferable that the Tama Device quartz crystal is guided in parallel with the orientation flat, and the MAXTEK quartz is preferably guided perpendicular to the orientation flat. .

  Since the quartz substrate used is AT cut, the refractive index ellipsoid is inclined with respect to the substrate surface. FIG. 21B and FIG. 22B are refractive index ellipses showing a cross section of the refractive index ellipsoid perpendicular to the direction of the optical path (parallel to the substrate in the light propagation direction). That is, the light propagation direction is a direction from the top to the bottom of the page. In such a display, the direction in which the refractive index ellipse is inclined with respect to the substrate surface and the axis of the refractive index ellipse may be perpendicular or parallel to the substrate surface. In FIG. 21B, the refractive index ellipse is not inclined, whereas in FIG. 22B, the refractive index ellipse is inclined. When the refractive index ellipse is tilted, as described with reference to FIGS. 4 to 6, the polarization plane may be rotated as light propagates. In the present invention, since the SPR generated only in a specific polarization plane is used, the rotation of the polarization plane varies depending on the optical path length, so that it is difficult to reproducibly produce the entire optical path length at the wavelength level. In order to obtain a good and reproducible SPR signal, it is preferable to select the light incident / exit direction and the light propagation direction so that the wavefront does not rotate.

  FIG. 22B is not preferable because a long axis and a short axis are inclined with respect to the substrate surface in the cross section of the ellipsoid in the ellipsoid pattern created by the measurement result of the refractive index. As shown in FIG. 21B, in the ellipsoidal pattern created by the refractive index measurement result, the major axis and the minor axis are perpendicular to or parallel to the substrate surface (or parallel and perpendicular). It is shown that it is preferable to set the propagation direction of light (determine the orientation of the measurement light and the reference light). For this reason, in the present application, since the crystal made by Tama Device Co., Ltd., whose X axis is perpendicular to the orientation flat is used, the measurement light and the reference light are propagated in a direction parallel to the orientation flat.

  Next, a result of measuring the reflection intensity using surface plasmon resonance by placing a metal thin film on the surface of a quartz substrate having a pattern in which the X axis is parallel to the orientation flat will be described as a reference example.

  In order to examine the SPR signal in a substrate having birefringence, such as a quartz substrate, the following experiment was attempted. SPR Measurement FIGS. 23 to 27 show the results of a single reflection SPR measurement using a conventional LaSFN9 prism. A gold thin film was deposited on one side of a quartz substrate manufactured by MAXTEK (AT cut, thickness 333 μm) to a thickness of 50 nm (a calibration curve was obtained in advance).

  A prism, a matching oil, a quartz substrate, and a gold thin film were arranged in this order, and the reflection intensity of p-polarized light was measured from the prism side using a HeNe laser having a wavelength of 632.8 nm as a light source and changing the incident angle and reflection angle. In FIGS. 23 to 26, the adjacent layer of the gold thin film is air. In FIG. 23, the measurement was performed with the quartz substrate placed so that the orientation flat was facing downward, and the surface formed by the incident light and the reflected light being a horizontal plane. In this arrangement, the polarization plane (horizontal) of the p-polarized light does not coincide with the optical axis of the crystal, so that it is predicted to be affected by birefringence. In the measurement result, as shown in FIG. 23, since the signal periodically varies with the angle, it is difficult to determine the absorption peak of SPR resonance. This signal variation is considered to be due to interference derived from the birefringence of the quartz substrate.

  FIG. 24 shows the measurement results in the same arrangement as in FIG. 23 except that the orientation flat of the quartz substrate is arranged upward. Also in FIG. 24, the p-polarization plane is horizontal and does not coincide with the optical axis of the quartz substrate. Since the signal fluctuates, it is difficult to determine the absorption peak of SPR resonance. This is considered to be due to interference derived from the birefringence of the quartz substrate.

  In FIG. 25, the quartz substrate is arranged so that the orientation flat is in the horizontal direction, and the light enters from the direction opposite to the orientation flat. A clear SPR signal was obtained as shown in FIG. In this arrangement, the p-polarization plane (horizontal) coincides with the direction of the optical axis of the quartz substrate, so that even if there is birefringence, the polarization plane does not rotate, so it is considered that a clear signal was observed. .

  In FIG. 26, the quartz substrate is arranged so that the orientation flat is in the horizontal direction, and is incident from the orientation flat direction. A clear SPR signal was obtained as shown in FIG. In this arrangement, as in FIG. 25, the p-polarization plane (horizontal) coincides with the optical axis direction of the quartz substrate, so that even if there is birefringence, the polarization plane does not rotate, so a clear signal is observed. It is thought that.

  In FIG. 27, the adjacent layer of the gold thin film, which was air in FIG. 26, was ethanol. Although the angle at which SPR is observed is shifted due to the difference in dielectric constant between air and ethanol, a clear signal is obtained. As described above, since the angle at which the reflected light intensity drops varies depending on the medium adjacent to the gold thin film, it can be determined that the signals observed in FIGS. 26 and 27 are based on SPR. Thus, when a metal thin film is formed on a quartz substrate and measured, in order to obtain an SPR signal clearly, in the single reflection, the surface normal created by the incident light and the outgoing light and the optical axis in the quartz substrate It was found that it is important to arrange the optical path in the direction that coincides with.

  When measuring with multiple reflections as in the present invention, for the same reason, in order to obtain a clear SPR signal, TE and TM polarized waves coincide with the optical axis of the quartz substrate in the propagation direction as an optical waveguide. It is effective to select the light propagation direction so as to obtain signal reproducibility.

  That is, it is only necessary to select an orientation in which the major axis and the minor axis of the ellipse in the cross section of the refractive index ellipsoid on the vertical plane of the light propagation direction are perpendicular to the crystal substrate surface and horizontal or vice versa.

  As described above, the relationship between the orientation of the incident light and the outgoing light and the substrate for clearly measuring the signal of the SPR measurement using the metal thin film on the substrate having birefringence such as the quartz substrate with high reproducibility is conventionally known. It has not been fully examined. In the present invention, as a result of intensive studies to construct a composite sensor of QCM, SPR and optical waveguide, the present invention has been achieved.

(Reference Example 1)
A single-reflection surface plasmon measurement optical system using a prism that is widely used, a quartz substrate made by MAXTEK having an X axis parallel to the orientation flat was used, and a metal thin film was placed on the surface of the quartz substrate. And the light parallel to the orientation flat was propagated. FIG. 23 is a measurement result when the orientation flat is faced down and the opposite surface of the quartz substrate is air, and is a characteristic diagram of angle and reflection intensity. From this measurement result, it can be seen that there are two peaks. FIG. 24 is a measurement result when the orientation flat is faced upward and the opposite surface of the quartz substrate is air, and is a characteristic diagram of angle and reflection intensity. It can be seen from this measurement result that there are two or more peaks. Thus, measurement in an orientation in which the original signal is difficult to discriminate by the interference pattern is not preferable from the viewpoint of reproducibility.

(Reference Example 2)
Next, using a quartz substrate manufactured by MAXTEK having a pattern in which the X axis is parallel to the orientation flat, a metal thin film was placed on the surface of the quartz substrate, and light perpendicular to the orientation flat was propagated. FIG. 25 shows the measurement results when the orientation flat is on the left and the opposite surface of the quartz substrate is air. From this measurement result, it can be seen that there is one peak. FIG. 26 shows the measurement results when the orientation flat is on the right side and the opposite surface of the quartz substrate is air. From this measurement result, it can be seen that there is one peak.

  Therefore, in the substrates having the pattern in which the crystal orientation X is parallel to the orientation flat from Examples 4 and 5, it is equivalent to propagating vertically compared to Example 4 corresponding to the propagation of light parallel to the orientation flat. It can be seen that a single peak with a clear peak position in Example 5 is obtained.

(Reference Example 3)
FIG. 27 shows the measurement result when the orientation flat is on the right side and the opposite surface of the quartz substrate is ethanol in the quartz substrate of Reference Example 2. It can be seen that the peak value of Reference Example 2 is based on surface plasmons.

  As an application example of the present invention, by selecting an adsorbent detection substance, detection and identification of an oxidizing gas such as nitrogen oxide, a basic gas such as ammonia, an organic solvent gas, a biological substance in a liquid, etc. Can be considered. Furthermore, it can be used for environmental monitoring and process management.

3 is a cross-sectional view of a substance adsorption detection sensor that is Embodiment 1. FIG. It is a top view of a substance adsorption detection sensor. It is a figure which shows the specific example of the dimension of a quartz substrate and two Ag electrodes. It is a figure which shows the incident place of the light to quartz. It is the characteristic which shows the wavelength (horizontal axis) and outgoing light intensity (vertical axis) with respect to s and p polarized light incidence when the incident place to the crystal is [1]. It is the characteristic which shows the wavelength (horizontal axis) and outgoing light intensity (vertical axis) with respect to s and p polarized light incidence when the incident place to the crystal is [2]. It is a block diagram of a substance adsorption detection system. It is a characteristic view which shows a measurement result when water vapor | steam is made into a measuring object in a substance adsorption detection system. It is a characteristic view which shows the repeated measurement result of water vapor | steam introduction. It is a characteristic view which shows a measurement result in the substance adsorption | suction detection system when ethanol vapor | steam was made into the measuring object. It is a characteristic view which shows the repeated measurement result of ethanol vapor | steam introduction | transduction. It is a characteristic view which shows a measurement result in the substance adsorption | suction detection system when acetone vapor | steam was made into the measuring object. It is a characteristic view which shows the repeated measurement result of acetone vapor | steam introduction | transduction. 6 is a top view of a substance adsorption detection sensor according to Embodiment 2. FIG. It is an absorbance spectrum characteristic view of Example 1, Example 2, and Example 3. It is a figure which shows the measurement result of Example 1. It is a figure which shows the measurement result of Example 2. It is a figure which shows the measurement result of Example 3. It is a figure for demonstrating the relationship between the surface orientation of an AT cut quartz substrate, and orientation flat. It is the figure which showed the relationship between a crystal direction and a cut surface (an orientation flat and a cut-out board surface). It is a figure which shows the refractive index measurement result in the board | substrate of a pattern whose X-axis is perpendicular | vertical to orientation flat. It is a figure which shows the refractive index measurement result in the board | substrate of a pattern whose X-axis is perpendicular | vertical to orientation flat. It is a measurement result characteristic view of reference example 1. It is another measurement result characteristic view of Reference Example 1. It is a measurement result characteristic figure of reference example 2. It is another measurement result characteristic view of Reference Example 2. It is a measurement result characteristic figure of reference example 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 .... Quartz substrate 2 .... Ag electrode 3 .... Ag electrode 4 .... Sensing layer 5 .... Base material 6 .... Quartz crystal resonator 10 ... Substance adsorption detection Sensor

Claims (2)

A quartz crystal unit is composed of a crystal part made of a single crystal crystal substrate and electrodes formed on both sides of the crystal part. The oscillation characteristics of the crystal unit and light guided by the crystal part as an optical waveguide In the substance adsorption detection method to be measured,
The optical waveguide is set so that one axis of a refractive index ellipse in a vertical section of the optical path of the optical waveguide is perpendicular to the quartz substrate,
One of the electrodes is also used as a metal thin film for surface plasmon resonance excitation, and reference light and measurement light are incident on the optical waveguide from the first end face of the crystal portion, and the measurement light is incident on the metal thin film in the optical waveguide. Exciting plasmon resonance to the reference light emitted from the optical waveguide to the second end face of the crystal portion and the intensity of the measurement light,
A sensitive material layer whose optical properties change due to substance adsorption is formed on one of the electrodes,
Changes in the optical characteristics due to the substance adsorbed on the sensitive material layer are detected by surface plasmons excited on one metal thin film of the electrode, and changes in the oscillation characteristics of the crystal resonator due to the adsorbed substance are detected. adsorption detection method comprising to Rukoto. A quartz crystal unit is composed of a crystal part made of a single crystal crystal substrate and electrodes formed on both sides of the crystal part. The oscillation characteristics of the crystal unit and light guided by the crystal part as an optical waveguide In the substance adsorption detection sensor to be measured,
The optical waveguide is set so that one axis of a refractive index ellipse in a vertical section of the optical path of the optical waveguide is perpendicular to the quartz substrate,
One of the electrodes is a metal thin film used for surface plasmon resonance excitation, and the crystal portion has a first end face as an incident end of the optical waveguide and a second end face as an exit end, and the first end face for reference light and measuring light emitted from said second end face entering shines on the optical waveguide from the metal thin film on an upper surface of the optical path of the measurement light are formed on the upper surface of the optical path the reference light Not formed,
The one formed on the electrode, material suction detecting sensor characterized that you have had a sensitive material layer whose optical characteristics are changed depending on the material adsorbed.

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