JP4926865B2 - Surface plasmon sensor - Google Patents

Description

  The present invention relates to a surface plasmon sensor that detects the refractive index of a liquid or a gas including a detection target using surface plasmon resonance.

  In recent years, many surface plasmon sensors using surface plasmon resonance have been developed. The surface plasmon sensor is used to detect the refractive index of a liquid or gas containing a detection target, and is widely used for measuring the concentration of a solution, detecting proteins and polymers, and the like. In addition, the surface plasmon sensor follows the time change of the refractive index of the liquid or gas containing the detection target, so that the detection process of the detection target to the adsorption layer that adsorbs the detection target of the metal film, the time change of the reaction, etc. Can also be detected.

  Here, a specific configuration of the surface plasmon sensor will be described using a surface plasmon sensor for measuring the concentration of the solution as an example. In the surface plasmon sensor, a metal film is formed on a dielectric substrate, and a detection target, for example, a predetermined molecule can be adsorbed on the surface of the metal film opposite to the side on which the dielectric substrate is formed. An adsorption layer is formed, and the molecule is adsorbed to the adsorption layer by bringing the solution containing the molecule into contact with the adsorption layer. The surface plasmon sensor detects the refractive index of the solution by irradiating the surface of the metal film opposite to the surface on which the adsorption layer is formed with a light beam emitted from a light source. Furthermore, the surface plasmon sensor also detects the refractive index of the solvent that does not contain the molecule as well as the refractive index of the solution, and from the refractive index change between the refractive index of the solvent and the refractive index of the solution, Determine the concentration of the solution.

  The surface plasmon sensor uses surface plasmon resonance to detect the refractive index. Surface plasmon resonance means that when a light beam is incident on a metal film on a dielectric substrate with an appropriate polarization direction and incident angle, the wave number of the light beam in a direction parallel to the metal film, the wave number of the surface plasmon, If they match, it is a phenomenon that causes resonance. The surface plasmon is a dense wave in which free electrons on the metal surface vibrate in a direction parallel to the metal surface.

  That is, in the surface plasmon sensor, when the light beam is irradiated onto the metal film, the light beam is incident on the metal film at an appropriate incident angle and polarization direction. Converted to surface plasmon. Therefore, the reflectance of the light beam with respect to the metal film becomes small because energy is used for the amount converted to surface plasmon.

  When the light beam is incident on the metal film with an appropriate incident angle and polarization direction, the relationship between the incident angle and the reflectance is expressed as a graph with the horizontal axis representing the incident angle and the vertical axis representing the reflectance. It can be seen that decreases at a certain incident angle. The portion where the reflectance is reduced is called dip. In the following description, the minimum value of the reflectance in the dip is defined as reflectance Rmin, and the incident angle at this time is defined as an incident angle θmin.

  That is, the appropriate incident angle is an incident angle θmin at which most of the light beam is converted to surface plasmon on the metal film. In addition, the appropriate polarization direction refers to a plane including the normal line of the interface formed between the dielectric substrate and the metal film and the optical axis of the light beam as an incident plane, with respect to the incident plane. Parallel polarization directions (p-polarized light). Note that the surface plasmon resonance does not occur when the polarization direction of the light beam is a polarization direction (s-polarized light) perpendicular to the incident surface.

  The surface plasmon sensor can calculate the refractive index of the solution from the relationship between the incident angle θmin calculated in advance and the refractive index of the solution by obtaining the incident angle θmin using surface plasmon resonance. .

  Non-Patent Document 1 describes that the thickness of the metal film and the incident angle θmin depend on the refractive index of the medium in contact with the metal film. Therefore, the relationship between the incident angle and the reflectance varies depending on the refractive index of the solvent or solution in contact with the metal film. Therefore, the surface plasmon sensor can detect a refractive index change between when the solvent not containing the molecule is brought into contact with the metal film and when the solution containing the molecule is brought into contact with the metal film. .

  The surface plasmon sensor can calculate the concentration of the solution from the relationship between the refractive index calculated in advance and the concentration of the solution by using the refractive index change.

  In general, the film thickness of the metal film of the surface plasmon sensor is the light when a liquid or gas not including the detection target is brought into contact with the metal film in order to detect an accurate refractive index of the liquid or gas including the detection target. The reflectance Rmin of the beam with respect to the metal film is selected to be the smallest. In the following description, the thickness of the metal film having the smallest reflectance Rmin is referred to as the thickness d.

  However, in the conventional surface plasmon sensor, when detecting the refractive index of a liquid or gas containing a detection target with absorption, even if the thickness of the metal film is set to the film thickness d, the light absorption characteristics of the detection target are The value of the incident angle θmin changes with the change. As a result, the conventional surface plasmon sensor has a problem that the correct refractive index of the liquid or gas including the detection target cannot be calculated.

  In order to detect an accurate refractive index of a liquid or gas including a detection target having absorption, the relationship between the incident angle θmin and the refractive index with respect to the extinction coefficient is previously determined for the liquid or gas including the detection target having a predetermined concentration. It is necessary to calculate or measure.

  However, although the relationship between the incident angle θmin and the refractive index is almost linear, the relationship between the extinction coefficient and the incident angle θmin is not linear, so the incident angle θmin for a fine change in the extinction coefficient is calculated or measured in advance. There is a need. Therefore, the calculation for calculating the refractive index, extinction coefficient, and concentration of the liquid or gas including the detection target from the incident angle θmin becomes very complicated.

Therefore, Patent Document 1 proposes the following two methods as means for solving the above problems. The first method is a method in which the wavelength of the light source is set to the absorption maximum wavelength of the detection target and the refractive index change caused by the light absorption change is measured. In the second method, the refractive index is obtained from the incident angle θmin, and the extinction coefficient is obtained from the change in reflectance.
JP 2001-242072 A (publication date: September 7, 2001) Surface Plasmons on smooth and rough surfaces and on gratings, Heinz Raether, Springer-Verlag, 1988 p.118-p.123

  However, the first method and the second method described in Patent Document 1 have the following problems, respectively.

  First, the first method uses the wavelength of the light source as the maximum absorption wavelength of the detection target, but is effective only when the wavelength of the light source is near the maximum absorption wavelength of the detection target, and the wavelength of the light source is the maximum absorption wavelength of the detection target. It cannot be applied if it is significantly different. Therefore, in the first method, it is necessary to always match the wavelength of the light source with the absorption maximum wavelength of the detection target. However, since the wavelength of the light source is limited and the wavelength cannot be set freely, there is a problem that the first method is not practical.

  In the second method, the refractive index is obtained from the incident angle θmin and the extinction coefficient is obtained from the reflection intensity. However, since the incident angle θmin also depends on the extinction coefficient, an accurate refractive index cannot be detected. . Further, as the extinction coefficient increases, the reflectance Rmin also increases, so that it is difficult to determine dip, and the S / N when detecting the incident angle θmin is deteriorated. As described above, in the second method, when detecting the refractive index of a liquid or gas containing a detection target having absorption, the accurate refractive index cannot be detected due to the influence of light absorption. , Detection accuracy will deteriorate.

  Furthermore, in the second method, in order to calculate the extinction coefficient, it is necessary to accurately obtain the reflection intensity, and both the p-polarized light and the s-polarized light are measured, and the transmittance for each polarization direction is determined for each. The incident angle must be corrected, and the operation becomes very complicated.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a surface plasmon sensor that can measure the refractive index of a detection target having absorption without being affected by light absorption with a simple configuration. Is to provide.

  In order to solve the above problems, the surface plasmon sensor of the present invention is formed on a light-transmitting dielectric substrate, and a light source is applied to a metal film in contact with a liquid or gas containing a detection target. A surface plasmon sensor that detects the refractive index of the liquid or the gas by irradiating the surface of the metal film opposite to the surface in contact with the liquid or the gas with the light beam emitted from the metal film. The thickness of the metal film is smaller than the thickness d at which the minimum reflectance of the light beam with respect to the metal film in contact with the liquid or the gas not including the detection target is minimized. It is said.

  In the conventional surface plasmon sensor, the thickness of the metal film is the thickness d. When the film thickness of the metal film is the film thickness d, the minimum value Rmin of the reflectance of the light beam with respect to the metal film when the extinction coefficient is 0, and the metal of the light beam at the reflectance Rmin The incident angle θmin with respect to the film is the minimum value. That is, the incident angle θmin and the reflectance Rmin are minimum values when the extinction coefficient is 0, and monotonously increase as the extinction coefficient increases. Therefore, in order to suppress the change in the incident angle θmin and the reflectance Rmin within a predetermined range, there arises a problem that only the detection target of the extinction coefficient in a narrow range can be measured.

  Therefore, in the surface plasmon sensor of the present invention, the incident angle θmin and the reflectance Rmin are minimized with a predetermined extinction coefficient value by making the thickness of the metal film smaller than the thickness d. Can do. That is, the incident angle θmin and the reflectance Rmin decrease once when the extinction coefficient is 0 to a predetermined value, and increase after the predetermined value.

  Therefore, in the surface plasmon sensor of the present invention, the change in the incident angle θmin and the reflectance Rmin at an extinction coefficient within a predetermined range as compared with the case where the thickness of the metal film is the thickness d. Can be halved. Therefore, even when a detection target with absorption is used, the incident angle θmin hardly depends on the extinction coefficient. Therefore, it is possible to accurately detect the refractive index of the detection target having absorption without being affected by light absorption with a simple configuration in which the metal film thickness of the conventional apparatus is simply reduced.

  Furthermore, since the surface plasmon sensor according to the present invention can suppress the fluctuation of the reflectance Rmin accompanying the increase of the extinction coefficient, it is possible to suppress the deterioration of S / N when the incident angle θmin is detected. In addition, since the relationship between the incident angle θmin and the refractive index and the relationship between the refractive index and the concentration are linear, not only the refractive index of the liquid or the gas but also the concentration is obtained from the incident angle by a very simple calculation. be able to.

  In the surface plasmon sensor of the present invention, the metal film is preferably made of gold.

  The liquid or gas containing the detection target is in direct contact with the metal film. Therefore, it is desirable that the metal film is made of a stable metal that does not cause a chemical reaction with the liquid or the gas. Gold is a very stable metal, has high durability because it does not rust, and excites surface plasmons efficiently. Therefore, by using gold as the metal film of the surface plasmon sensor of the present invention, a chemical reaction is not caused by the liquid or the gas including the detection target, and the refractive index of the liquid or the gas is detected with high resolution. Further, deterioration with time due to oxidation of the metal film can be prevented.

  In the surface plasmon sensor of the present invention, the wavelength of the light source may be about 600 nm to about 1550 nm.

  In order to excite surface plasmons on the metal film, the wavelength of the light beam emitted from the light source is important. As described above, the metal film is most preferably made of gold. However, in order to excite surface plasmons on the metal film made of gold, a light beam having a wavelength of about 600 nm to about 1550 nm is used. It is desirable to irradiate the metal film. By irradiating the metal film composed of gold with a light beam having a wavelength of about 600 nm to about 1550 nm from the light source, the excitation efficiency of surface plasmon is increased, and the liquid or gas containing the detection target with high resolution Can be detected.

  In the surface plasmon sensor of the present invention, the difference between the thickness of the metal film and the thickness d may be about 20 nm or less.

  When the film thickness of the metal film is the film thickness d, in order to suppress changes in the incident angle θmin and the reflectance Rmin within a predetermined range, only a detection object having a narrow extinction coefficient can be measured. A malfunction occurs.

  In addition, when the thickness of the metal film is set to a value that is significantly different from the thickness d, the extinction coefficient in a narrow range can be detected as in the case where the thickness of the metal film is set to the thickness d. There is a problem that only the target can be measured.

  Therefore, in the surface plasmon sensor of the present invention, the difference between the thickness of the metal film and the film thickness d is set to about 20 nm or less, so that the fluctuation of the incident angle θmin accompanying the increase in the extinction coefficient is reduced. It can be suppressed than in the case of. In addition, since the fluctuation of the reflectance Rmin can also be suppressed as compared with the case of the film thickness d, it is possible to suppress the deterioration of S / N when the incident angle θmin is detected.

  In the surface plasmon sensor of the present invention, the difference between the thickness of the metal film and the thickness d may be about 10 nm to about 15 nm.

  With the above configuration, the fluctuation of the incident angle θmin accompanying the increase in the extinction coefficient can be sufficiently reduced, for example, to about 1/10 of dip. Therefore, the range of the extinction coefficient of the detection target that can detect the accurate refractive index of the liquid or the gas including the detection target can be maximized. In addition, since the fluctuation of the reflectance Rmin in the range of the extinction coefficient can be suppressed to less than half compared with the case where the thickness of the metal film is the thickness d, the S / at the time of detecting the incident angle θmin is reduced. N deterioration can be suppressed.

  In the surface plasmon sensor of the present invention, the dielectric substrate may be configured to be detachable from the surface plasmon sensor.

  Since the dielectric substrate on which the metal film is formed is detachable from the surface plasmon sensor, it is possible to replace the metal film with the dielectric substrate according to the detection target. As a result, it is possible to detect a variety of detection targets using a single device. That is, the sensitivity, measurement range, and the like of the surface plasmon sensor can be changed by replacing with a dielectric substrate made of another material and having a metal film having another film thickness.

  Moreover, in the surface plasmon sensor of this invention, you may equip the metal film surface with the adsorption layer which adsorb | sucks a specific molecule | numerator.

  There is a possibility that a substance other than the detection target is mixed in the liquid or gas containing the detection target. In that case, when the refractive index of the liquid or the gas is detected by a surface plasmon sensor, the concentration containing the detection target and the substance is detected.

  Therefore, by adopting the above-described configuration of the present invention, it is possible to adsorb only a predetermined molecule, which is a detection target, and to know the concentration of only the molecule.

  As described above, the surface plasmon sensor of the present invention is formed on the dielectric substrate, and the light beam emitted from the light source is applied to the metal film in contact with the liquid or gas containing the detection target. A surface plasmon sensor that detects the refractive index of the liquid or the gas by irradiating the surface of the metal film opposite to the surface in contact with the liquid or the gas, wherein the film thickness of the metal film Is characterized in that the minimum value of the reflectance of the light beam with respect to the metal film in contact with the liquid or the gas not including the detection target is smaller than the film thickness d at which the minimum value is minimized.

  Therefore, in the surface plasmon sensor of the present invention, the incident angle θmin and the reflectance Rmin are minimized with a predetermined extinction coefficient value by making the thickness of the metal film smaller than the thickness d. Can do. That is, the incident angle θmin and the reflectance Rmin decrease once when the extinction coefficient is 0 to a predetermined value, and increase after the predetermined value.

  Therefore, in the surface plasmon sensor of the present invention, the change in the incident angle θmin and the reflectance Rmin at an extinction coefficient within a predetermined range as compared with the case where the thickness of the metal film is the thickness d. Can be halved. Therefore, even when a detection target with absorption is used, the incident angle θmin hardly depends on the extinction coefficient. Therefore, it is possible to accurately detect the refractive index of the detection target having absorption without being affected by light absorption with a simple configuration in which the metal film thickness of the conventional apparatus is simply reduced.

  Furthermore, since the surface plasmon sensor of the present invention can suppress the change in reflectance accompanying an increase in the extinction coefficient, it is possible to suppress the deterioration of S / N at the time of detecting the incident angle. In addition, since the relationship between the incident angle and the refractive index and the relationship between the refractive index and the concentration are linear, it is possible to obtain not only the refractive index of the liquid or the gas but also the concentration from the incident angle by a very simple calculation. Can do.

  An embodiment of the present invention will be described below with reference to FIGS.

  The surface plasmon sensor of the present invention is formed on a light-transmitting dielectric substrate, and a light beam emitted from a light source is applied to a metal film in contact with a liquid or gas containing a detection target. By irradiating the surface of the metal film opposite to the surface in contact with the liquid or the gas, the refractive index of the liquid or the gas is detected.

  In the present invention, the film thickness of the metal film is thinner than the film thickness d at which the minimum value of the reflectance of the light beam in the metal film in contact with the liquid or the gas not including the detection target is minimized. It is characterized by.

[Overall configuration of surface plasmon sensor]
First, an overall configuration of an embodiment of a surface plasmon sensor according to the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing an outline of the overall configuration of an embodiment of a surface plasmon sensor according to the present invention.

  As shown in FIG. 1, the surface plasmon sensor 1 includes a light source 2, a collimating lens 3, a condenser lens 4, a prism (dielectric substrate) 5, a metal film 6, a first lens 7, and a second lens. A lens 8, a photodetector 9, a light source drive circuit 10, a calculation circuit 11, and a monitor 12 are provided.

  The surface plasmon sensor 1 of the present embodiment detects the refractive index of a sample (liquid or gas containing a detection target) 14 and is suitably used for measuring the concentration of the sample 14, detecting proteins, polymers, and the like. . In addition, as the sample 14, the liquid or gas containing a detection target is mentioned.

  The light source 2 emits a light beam 13, and a semiconductor laser, a light emitting diode, or the like is preferably used. The light beam 13 emitted from the light source 2 is irradiated onto the metal film 6 to excite surface plasmons on the surface of the metal film 6. Here, when the light beam 13 includes a plurality of wavelengths, the excitation conditions of the surface plasmon at each wavelength are different. Therefore, the incident angle dependence of the reflected light reflected by the metal film 6 is different, and the analysis becomes complicated. Therefore, it is desirable that the wavelength region of the light source 2 be as narrow as possible.

  Further, the polarization direction of the light beam 13 emitted from the light source 2 is such that the normal line of the interface formed between the prism 5 and the metal film 6 and the surface including the optical axis of the light beam 13 are incident surfaces. Sometimes, a polarization direction parallel to the incident surface, that is, p-polarized light is desirable. The light beam 13 can excite surface plasmons on the surface of the metal film 6 by setting the polarization direction to p-polarized light. When the polarization direction of the light beam 13 is a polarization direction perpendicular to the incident surface, that is, s-polarized light, the light beam 13 cannot excite surface plasmons on the surface of the metal film 6.

  The collimating lens 3 converts the light beam 13 emitted from the light source 2 into parallel light. The shorter the focal length of the collimating lens 3 is, the higher the utilization efficiency of the light beam 13 emitted from the light source 2 is.

  The condensing lens 4 condenses the light beam 13 emitted from the light source 2 on the metal film 6. By converting the light beam 13 emitted from the light source 2 by the collimator lens 3 into parallel light, the condenser lens 4 can efficiently collect the light beam 13 on the metal film 6. Further, the condenser lens 4 can make the light beam 13 incident on the metal film 6 at various incident angles by adjusting the position.

  As the condensing lens 4, a lens such as a plano-convex lens that condenses all directions may be used, or a lens such as a cylindrical lens that condenses only in one direction may be used. When a lens that collects all directions is used as the condenser lens 4, the incident angle to the metal film 6 is complicated, but the irradiation area can be reduced. Therefore, the surface plasmon sensor 1 using a lens that collects all directions can obtain local information of the sample 14.

  Further, when a lens that collects light in only one direction is used as the condenser lens 4, the incident angle to the metal film 6 depends only on the direction of light collection because the non-condensing direction remains the original beam size. To do. Therefore, the surface plasmon sensor 1 using a lens that collects light in only one direction can easily analyze the sample 14 and can increase the irradiation area of the light beam 13, thereby obtaining overall information of the sample 14. Can do.

  The angle range of the incident angle on the metal film 6 is determined by the numerical aperture of the condenser lens 4. When the sample 14 is in contact with the metal film 6, surface plasmons are excited on the metal film 6. It is necessary to decide. Furthermore, it is also preferable to set the range of the incident angle to the metal film 6 so that all the light beams 13 are totally reflected. The collimating lens 3 and the condensing lens 4 are configured to collect light after collimated once, but a single finite lens may be used instead.

  The prism 5 is a translucent dielectric substrate, and passes the light beam 13 emitted from the light source 2 to irradiate the metal film 6 with the light beam 13 at an arbitrary incident angle. It excites surface plasmons. The material constituting the prism 5 is not particularly limited as long as it can transmit the wavelength of the light source 2 and can excite surface plasmons on the metal film 6, but glass, resin, or the like is preferably used.

  In order to efficiently excite surface plasmons on the surface of the metal film 6, it is desirable to irradiate the metal film 6 with the light beam 13 at an incident angle of about 45 degrees. However, it is difficult to make the light beam 13 enter the metal film 6 through the parallel substrate instead of the prism 5 at an incident angle of about 45 degrees. Therefore, the surface plasmon sensor 1 of the present embodiment uses the prism 5 to irradiate the metal film 6 with the light beam 13 at an incident angle of about 45 degrees.

  As the prism 5, a triangular prism is used in FIG. 1, but a trapezoidal, wedge-shaped, semi-cylindrical, hemispherical prism, or the like is also preferably used. For example, when a semi-cylindrical or hemispherical prism is used as the prism 5, when the light beam 13 is incident toward the center of the semi-cylindrical and hemisphere, the angle of incidence on the incident surface of the prism is almost a right angle. The reflectance at the incident surface is reduced, and the light utilization efficiency is increased.

  Further, when a semi-cylindrical prism is used as the prism 5, when the light beam 13 is incident toward the center of the semi-cylinder, the incident angle to the incident surface of the prism is equal to the incident angle to the metal film 6. Therefore, it is not necessary to convert the incident angle.

  In addition, when a triangular prism is used as the prism 5, the incident angle to the prism and the incident angle to the metal film 6 are different due to refraction at the incident surface, but it is cheaper than a semi-cylindrical prism. Generally used. The prism 5 is not limited to the above-described configuration, and may have another shape or a waveguide as long as it can enter the metal film 6 at an appropriate angle.

  The metal film 6 generates surface plasmons by the light beam 13 emitted from the light source 2. The metal film 6 may be directly formed on a predetermined surface of the prism 5, or may be formed on a dielectric substrate having a refractive index similar to that of the prism 5, and the metal film 6 of the dielectric substrate is formed on the dielectric substrate. The surface opposite to the formed side may be placed on a predetermined surface of the prism 5 with an index matching agent interposed therebetween. As the index matching agent, a commercially available liquid or gel may be used, or a UV curable resin may be used. However, if the dielectric substrate on which the metal film 6 is formed tilts, an error in incident angle occurs. Therefore, it is necessary to use an index matching agent that can stably fix the dielectric substrate on the prism 5. Further, in order to improve the adhesion with the dielectric substrate or the prism 5 and to improve the surface accuracy of the metal film 6, a base layer may be provided between the dielectric substrate or the prism 5 and the metal film 6. .

  In addition, by making the dielectric substrate on which the metal film 6 is formed detachable from the prism 5, it is possible to replace the metal film with the dielectric substrate according to the detection target. As a result, it is possible to detect various samples 14 using one apparatus. That is, the sensitivity, measurement range, etc. of the surface plasmon sensor 1 can be changed by replacing with a dielectric substrate made of another material and having a metal film 6 having another film thickness.

  Note that the predetermined one surface of the prism 5 is a surface including the base of the triangle when the prism 5 is the triangular prism shown in FIG. 1, and a semi-cylindrical or hemispherical when the prism 5 is a semi-cylindrical or hemispherical prism. It is a surface including the center of the mold, and is a surface on which the light beam 13 can be incident on the metal film 6 by the prism 5 at an incident angle of about 45 degrees.

  Further, an adsorption layer capable of adsorbing specific molecules on the surface of the metal film 6 may be provided to detect specific molecules in the sample 14. There is a possibility that a substance other than the detection target is mixed in the sample 14. In that case, when the refractive index of the sample 14 is detected by the surface plasmon sensor 1, the concentration containing the detection target and the substance is detected. Therefore, by providing the adsorption layer on the metal film 6, it is possible to adsorb only the detection target and know the concentration of only the detection target.

  The material constituting the metal film 6 may be any metal or alloy that can excite surface plasmons. For example, silver, copper, aluminum, platinum, gold, or the like is preferably used. The metal film 6 is preferably made of a stable metal that does not cause a chemical reaction by the sample 14 in order to directly contact the sample 14.

  Among the metals described above, gold is a very stable metal and has high durability because it does not rust. Further, it excites surface plasmons efficiently. Therefore, gold is most preferably used as the metal film of the surface plasmon sensor 1. By using gold as the metal film 6, it is possible to detect the refractive index with high resolution without causing a chemical reaction by the sample 14, and to prevent deterioration with time due to oxidation of the metal film. When the metal film 6 is made of gold, it is desirable to irradiate the metal film 6 with the light beam 13 having a wavelength of about 600 nm to about 1550 nm in order to excite surface plasmons on the metal film 6. By irradiating the metal film 6 made of gold with the light beam 13 having a wavelength of about 600 nm to about 1550 nm from the light source 2, the excitation efficiency of the surface plasmon is increased, and the refractive index of the sample 14 can be detected with high resolution. it can.

  Further, as shown in Non-Patent Document 1, the film thickness of the metal film 6 is mainly determined by the refractive index of the sample 14 depending on the refractive index of the prism 5, the metal film 6 and the sample 14, and the wavelength of the light source 2. The film thickness is determined to be suitable for detecting the rate. As described above, in the related art, the film thickness of the metal film 6 is set to the film thickness d that minimizes the minimum reflectance of the light beam 13 in the metal film 6 in contact with the sample 14 that does not include the detection target. Usually, it is about several tens of nm. However, the present invention is characterized in that a film thickness smaller than this film thickness d is used, and details thereof will be described later.

  The first lens 7 and the second lens 8 are for condensing the light beam 13 reflected at the interface formed between the prism 5 and the metal film 6 to the photodetector 9 and making it incident. The first lens 7 and the second lens 8 have a configuration in which the reflected light from the interface is once converted into parallel light and then condensed on the photodetector 9. However, the present invention is not limited to this, and is limited to one finite system. A lens may be used.

  The photodetector 9 detects the intensity of the reflected light reflected by the light beam 13 at the interface formed between the prism 5 and the metal film 6. As the photodetector 9, it is preferable to capture reflected light at a time by using a CCD or CMOS or an array detector. In particular, if a CCD or CMOS is used as the photodetector 9, it is possible to select which light beam of the light beam 13 is used for measurement.

  The light source driving circuit 10 drives the light source 2 and drives the light source 2 by receiving a voltage supplied from a power source (not shown) and causing a current to flow through the light source 2. In order to prevent the light source 2 from being destroyed, it is preferable that the light source driving circuit 10 is provided with an upper limit value for the current value flowing through the light source 2.

  The calculation circuit 11 calculates the refractive index of the sample 14 from the detection result of the photodetector 9. Specifically, the calculation circuit 11 calculates the incident angle θmin of the light beam 13 to the metal film 6 from the reflected light intensity of the light beam 13 detected by the photodetector 9. Then, the calculation circuit 11 calculates the refractive index corresponding to the calculated incident angle θmin from the relationship between the incident angle θmin and the refractive index input in advance. Here, when it is assumed that the sample 14 is of one type, the calculation circuit 11 further calculates the concentration corresponding to the calculated refractive index from the relationship between the refractive index and the concentration input in advance. You can also

  In general, the relationship between the incident angle θmin and the refractive index and the relationship between the refractive index and the concentration can be linearly approximated. Therefore, not only the refractive index of the sample 14 but also the concentration can be obtained from the incident angle θmin by a very simple calculation. Further, the calculation circuit 11 may include a storage unit that stores the detection result of the surface plasmon sensor 1. As the calculation circuit 11, a semiconductor chip such as an LSI or an IC, a computer that combines these, or the like is preferably used.

  The monitor 12 displays various results such as the measurement result stored in the calculation circuit 11, the true reflectance calculated from the measurement result, and the refractive index and concentration of the sample 14 determined from the reflectance. . As the monitor 12, for example, a CRT or a liquid crystal display is preferably used.

  Next, a method for detecting the refractive index of the sample 14 using the surface plasmon sensor 1 of the present embodiment will be described with reference to FIGS. FIG. 2 is a diagram showing an embodiment of a method for contacting the sample 14 with the metal film 6 of the surface plasmon sensor 1. FIG. 3 is a diagram showing another embodiment of a method for contacting the sample 14 with the metal film 6 of the surface plasmon sensor 1. The sample 14 is a target whose refractive index is detected by the surface plasmon sensor 1, and is a liquid or gas containing a predetermined molecule.

  First, the surface plasmon sensor 1 of the present embodiment brings the sample 14 into contact with the surface of the metal film 6 in order to detect the refractive index of the sample 14. For example, when a liquid is used as the sample 14, as shown in FIG. 2, the surface of the metal film 6 opposite to the side where the prism 5 is provided is brought into contact as a droplet. Further, for example, when liquid or gas is used as the sample 14, as shown in FIG. 3, the liquid or gas is caused to flow and contact the flow cell 15 provided on the surface of the metal film 6. The method of bringing the sample 14 into contact with the surface of the metal film 6 is not limited to the above-described method, and any configuration that allows the sample 14 to contact the surface of the metal film 6 may be used.

  Then, after bringing the sample 14 into contact with the surface of the metal film 6, the light beam 13 is emitted from the light source 2. Then, the light beam 13 is converted into parallel light by the collimator lens 3, and with respect to the interface formed between the prism 5 and the metal film 6 via the prism 5 at various incident angles by the condenser lens 4. The metal film 6 is irradiated with p-polarized light. The light beam 13 is reflected by the metal film 6, and the reflected light is condensed on the photodetector 9 via the first lens 7 and the second lens 8. Then, the incident angle dependence of the reflected light intensity of the reflected light collected on the photodetector 9 is measured and displayed on the monitor 12.

  Further, the calculation circuit 11 calculates the incident angle θmin from the reflected light intensity of the light beam 13 detected by the photodetector 9. Then, the refractive index of the sample 14 corresponding to the calculated incident angle θmin is calculated from the relationship between the incident angle θmin and the refractive index input in advance. Further, the calculation circuit 11 can calculate the concentration of the sample 14 corresponding to the calculated refractive index by inputting the relationship between the refractive index and the concentration in advance.

[Selection of film thickness of metal film 6]
Next, a method for selecting the film thickness of the metal film 6 will be described with reference to FIGS. As described above, the thickness of the metal film 6 is selected according to the refractive index in the state that does not include the detection target of the prism 5, the metal film 6, and the sample 14, and the wavelength of the light source 2. can do. Below, a typical example is demonstrated about the value which each said element used for selection of the film thickness of the metal film 6 can take.

  As the refractive index of the prism 5, a refractive index of 1.46 of quartz generally used for a prism and a refractive index of 2.0 having a high refractive index are used. As a material for the prism, not only quartz but also glass is preferably used. However, the refractive index of general glass is about 1.5, which is almost the same as the case of quartz.

  The refractive index of the metal film 6 depends on the material constituting the metal film 6, and various materials can be considered as the material constituting the metal film 6 as described above. However, in the following description, Au is used as the material of the metal film 6.

  As the refractive index of the sample 14 that does not include the detection target, there are a case where the sample 14 is a liquid including the detection target and a case where the sample 14 is a gas including the detection target. Therefore, when the sample 14 is a liquid containing a detection target, it is assumed that the concentration is measured by dissolving the detection target in water, and the refractive index 1.33 of the solvent before dissolving the detection target, that is, water is used. Further, when the sample 14 is a gas containing a detection target, it is assumed that the concentration is assumed by melting the detection target in air or vacuum, and a refractive index of 1.0 before the detection target is dissolved is used.

  When the material constituting the metal film 6 is Au, the wavelength of the light source 2 is in the red to infrared range suitable for exciting surface plasmons on the metal film 6. Specifically, in the following description, wavelengths of 635 nm and 780 nm of a semiconductor laser and a wavelength of 1054 nm of a YAG laser are used.

  Hereinafter, selection of the thickness of the metal film 6 in the case where the above four elements are combined will be described with reference to the first to third embodiments. However, when the prism 5 is made of quartz and the sample 14 is made of liquid, the surface plasmon can hardly be excited in the metal film 6, so this configuration is excluded.

[First embodiment]
First, a first embodiment for selecting the film thickness of the metal film 6 will be described with reference to FIGS. In the present embodiment, as the above four elements, Au is used as the material of the metal film 6, the wavelengths of the light source 2 are 635 nm, 780 nm, and 1054 nm, the refractive index of the prism 5 is 2.0, and the sample 14 is detected. The selection of the film thickness of the metal film 6 in the case where 1.33 is selected as the refractive index in a state not including the target will be described.

  First, the relationship between the incident angle of the light beam 13 with respect to the metal film 6 and the reflectance at each wavelength of the light source 2 when the extinction coefficient is 0 for the above four elements will be described with reference to FIG. FIG. 4 shows the relationship between the incident angle and the reflectance of the light beam 13 having the respective wavelengths of 635 nm, 780 nm, and 1054 nm emitted from the light source 2 when the extinction coefficient is 0 for the above four elements. It is a graph to show. In the figure, the dotted line indicates the wavelength 635 nm of the light beam 13, the broken line indicates the wavelength 780 nm of the light beam, and the solid line indicates the wavelength 1054 nm of the light beam.

  Further, the thickness of the metal film 6 at each wavelength of the light beam 13 emitted from the light source 2 is such that the minimum value Rmin of the reflectance is close to 0, and the metal film 6 when the wavelength of the light beam 13 is 635 nm. When the wavelength of the light beam 13 is 780 nm, the thickness of the metal film 6 is 45 nm. When the wavelength of the light beam 13 is 1054 nm, the thickness of the metal film 6 is 35 nm.

  As shown in FIG. 4, the full width at half maximum of dip in which the reflectance at each wavelength of the light beam 13 falls is about 3.4 degrees when the wavelength of the light beam 13 is 635 nm, and about 0 when the wavelength of the light beam 13 is 780 nm. It can be seen that when the wavelength of the light beam 13 is 1054 nm, it is about 0.5 degree.

  Next, selection of the film thickness of the metal film 6 at each wavelength of the light source 2 when the extinction coefficient is increased from 0 in consideration of the light absorption of the sample 14 will be described.

[Wavelength 635nm]
First, when the wavelength of the light beam 13 is 635 nm, the relationship between the extinction coefficient of the sample 14, the incident angle θmin, and the reflectance Rmin when the thickness of the metal film 6 is 30 nm, 35 nm, and 50 nm is shown. This will be described with reference to FIG. 5 (a) and FIG. 5 (b). FIG. 5A is a graph showing the relationship between the extinction coefficient of the sample 14 and the incident angle θmin when the wavelength of the light beam is 635 nm, and FIG. 5B is the graph of FIG. 5B where the wavelength of the light beam is 635 nm. It is the graph which showed the relationship between the extinction coefficient of the sample 14, and reflectance Rmin in the case. A dotted line indicates a film thickness of 30 nm, a broken line indicates a film thickness of 35 nm, and a solid line indicates a film thickness of 50 nm.

  When the thickness of the metal film 6 is 50 nm, which is the thickness d of the wavelength 635 nm of the light beam 13, the incident angle increases as the extinction coefficient increases from 0 to 0.09 as shown in FIG. It can be seen that θmin increases by about 0.7 degrees. The increased value of the incident angle θmin is about 1/5 of the full width at half maximum (about 3.4 degrees) of the dip described above, and is a range that is detected as an error. This error in the incident angle θmin is detected as a refractive index of 1.344 in a state where the detection target of the sample 14 is not included. Further, the value of the reflectance Rmin also increases as the extinction coefficient increases, as shown in FIG. This is a reduction in S / N at the time of detecting the incident angle θmin.

  When the thickness of the metal film 6 is 35 nm, as shown in FIG. 5A, the incident angle θmin increases by about 0.4 degrees as the extinction coefficient increases from 0 to 0.09. This is about 1/10 of the full width at half maximum (about 3.4 degrees) of dip described above, and is an angle shift that cannot be detected. Further, as shown in FIG. 5B, the value of the reflectance Rmin is also suppressed to a fluctuation of about half compared with the case of 50 nm.

  Further, when the thickness of the metal film 6 is 30 nm, as shown in FIGS. 5A and 5B, the incident angle θmin and the reflectance Rmin are about the same as the case where the thickness d is 50 nm. It turns out that it is a change.

  From the above, when the wavelength of the light beam 13 is 635 nm, the change of the incident angle θmin is suppressed to about 1/10 of the full width at half maximum of dip when the thickness of the metal film 6 is 50 nm which is the film thickness d. It can be seen that there is a problem that only the sample 14 having an extinction coefficient in the range of 0 to 0.05 can be measured. However, the influence of the absorption of the sample 14 on the incident angle θmin can be reduced by setting the thickness of the metal film 6 to 35 nm, that is, a thickness thinner than the thickness d. However, if the thickness of the metal film 6 is reduced to 30 nm, the same problem as when the thickness of the metal film 6 is set to the film thickness d occurs.

  Therefore, when the wavelength of the light beam 13 is 635 nm, the thickness of the metal film 6 is reduced within the range of about 0 nm to about 20 nm with respect to the thickness d of the metal film 6, thereby providing the metal of the light beam 13. It can be seen that the incident angle θmin and the reflectance Rmin with respect to the film 6 are less influenced by changes in the extinction coefficient than when the thickness of the metal film 6 is set to the film thickness d.

[Wavelength 780nm]
Next, when the wavelength of the light beam 13 is 780 nm, the relationship between the extinction coefficient of the sample 14, the incident angle θmin, and the reflectance Rmin when the film thickness of the metal film 6 is 30 nm, 35 nm, and 45 nm. This will be described with reference to FIG. FIG. 6A is a graph showing the relationship between the extinction coefficient of the sample 14 and the incident angle θmin when the wavelength of the light beam is 780 nm, and FIG. 6B shows the relationship between the wavelength of the light beam of 780 nm. It is the graph which showed the relationship between the extinction coefficient of the sample 14, and reflectance Rmin in the case. In addition, when a dotted line has a film thickness of 30 nm, a broken line has a film thickness of 35 nm, and a solid line has a film thickness of 45 nm.

  When the thickness of the metal film 6 is 45 nm, which is the thickness d of the wavelength of the light beam 13, the incident angle increases as the extinction coefficient increases from 0 to 0.025 as shown in FIG. It can be seen that θmin increases by about 0.16 degrees. The increased value of the incident angle θmin is about 1/5 of the full width at half maximum (about 0.8 degrees) of the above-described dip, and is a range that is detected as an error. The error of the incident angle θmin is detected as a refractive index of 1.334 in a state that does not include the detection target of the sample 14. Further, the value of the reflectance Rmin also increases as the extinction coefficient increases as shown in FIG. This is a reduction in S / N at the time of detecting the incident angle θmin.

  When the thickness of the metal film 6 is 35 nm, as shown in FIG. 6A, the incident angle θmin increases by about 0.08 degrees as the extinction coefficient increases from 0 to 0.025. . This is about 1/10 of the full width at half maximum of dip (about 0.8 degrees) described above, and is an angle shift that cannot be detected. As shown in FIG. 5B, the value of the reflectance Rmin is also suppressed to a fluctuation of about half compared with the case of 45 nm.

  Further, when the thickness of the metal film 6 is 30 nm, as shown in FIGS. 6A and 6B, the incident angle θmin and the reflectance Rmin are about the same as the case where the thickness d is 45 nm. It turns out that it is a change.

  From the above, when the wavelength of the light beam 13 is 780 nm, in order to suppress the change in the incident angle θmin to about 1/10 of the full width at half maximum of dip when the thickness of the metal film 6 is 45 nm which is the film thickness d. Shows that there is a problem that only the sample 14 having an extinction coefficient in the range of 0 to 0.018 can be measured. However, the influence of the absorption of the sample 14 on the incident angle θmin can be reduced by setting the thickness of the metal film 6 to 35 nm, that is, a thickness thinner than the thickness d. However, if the thickness of the metal film 6 is reduced to 30 nm, the same problem as when the thickness of the metal film 6 is set to the film thickness d occurs.

  Therefore, when the wavelength of the light beam 13 is 780 nm, the thickness of the metal film 6 is reduced within the range of about 0 nm to about 15 nm with respect to the film thickness d of the metal film 6. It can be seen that the incident angle θmin and the reflectance Rmin with respect to the film 6 are less influenced by changes in the extinction coefficient than when the thickness of the metal film 6 is set to the film thickness d.

[Wavelength 1054nm]
Next, when the wavelength of the light beam 13 is 1054 nm, the extinction coefficient of the sample 14 when the film thickness of the metal film 6 is 22.5 nm, 25 nm, and 35 nm, the incident angle θmin, and the reflectance Rmin The relationship will be described with reference to FIG. FIG. 7A is a graph showing the relationship between the extinction coefficient of the sample 14 and the incident angle θmin when the wavelength of the light beam is 1054 nm, and FIG. 7B shows the relationship between the light beam wavelength of 1054 nm. It is the graph which showed the relationship between the extinction coefficient of the sample 14, and reflectance Rmin in the case. In addition, the case where the dotted line is a film thickness of 22.5 nm, the broken line is the film thickness of 25 nm, and the solid line is the film thickness of 35 nm is shown.

  When the film thickness of the metal film 6 is 35 nm, which is the film thickness d of the wavelength of the light beam 13, the incident angle increases as the extinction coefficient increases from 0 to 0.02, as shown in FIG. It can be seen that θmin increases by about 0.09 degrees. The increased value of the incident angle θmin is about 1/5 of the full width at half maximum (about 0.5 degrees) of the dip described above, and is a range that is detected as an error. The error of the incident angle θmin is detected as a refractive index of 1.332 that does not include the detection target of the sample 14. Also, the value of the reflectance Rmin increases as the extinction coefficient increases, as shown in FIG. 7B. This is a reduction in S / N at the time of detecting the incident angle θmin.

  When the thickness of the metal film 6 is 25 nm, the increment of the incident angle θmin when the extinction coefficient increases from 0 to 0.02 is about 0.05 degrees. This is an angle shift that is about 1/10 of the full width at half maximum of dip and cannot be detected. Further, the reflectance Rmin when the extinction coefficient is increased is also suppressed to a fluctuation of half or less compared to the case of 35 nm.

  When the film thickness of the metal film 6 is 22.5 nm, as shown in FIGS. 7A and 7B, the incident angle θmin and the reflectance Rmin are equivalent to the film thickness d of 35 nm. It turns out that it is a change of a grade.

  From the above, when the wavelength of the light beam 13 is 1054 nm, in order to suppress the change in the incident angle θmin to about 1/10 of the full width at half maximum of dip when the thickness of the metal film 6 is 35 nm which is the film thickness d. Shows that there is a problem that only the sample 14 having an extinction coefficient in the range of 0 to 0.012 can be measured. However, the influence of the absorption of the sample 14 on the incident angle θmin can be reduced by setting the thickness of the metal film 6 to 25 nm, that is, a thickness thinner than the thickness d. However, if the thickness of the metal film 6 is reduced to 22.5 nm, the same problem as when the thickness of the metal film 6 is set to the film thickness d occurs.

  Therefore, when the wavelength of the light beam 13 is 1054 nm, the thickness of the metal film 6 is reduced within the range of about 0 nm to about 12.5 nm with respect to the thickness d of the metal film 6. It can be seen that the incident angle θmin and the reflectance Rmin with respect to the metal film 6 are less affected by the change in the extinction coefficient than when the film thickness of the metal film 6 is set to the film thickness d.

[Second Embodiment]
Next, a second embodiment for selecting the film thickness of the metal film 6 will be described with reference to FIGS. In the present embodiment, as the above four elements, Au is used as the material of the metal film 6, the wavelengths of the light source 2 are 635 nm, 780 nm, and 1054 nm, the refractive index of the prism 5 is 2.0, and the sample 14 is detected. The selection of the film thickness of the metal film 6 in the case where 1.0 is selected as the refractive index in a state not including the target will be described.

  First, the relationship between the incident angle of the light beam 13 with respect to the metal film 6 and the reflectance at each wavelength of the light source 2 when the extinction coefficient is 0 for the above four elements will be described with reference to FIG. FIG. 8 shows the relationship between the incident angle and the reflectance of the light beam 13 having the respective wavelengths of 635 nm, 780 nm, and 1054 nm emitted from the light source 2 when the extinction coefficient is 0 for the above four elements. It is a graph to show. In the figure, the dotted line indicates the wavelength 635 nm of the light beam 13, the broken line indicates the wavelength 780 nm of the light beam, and the solid line indicates the wavelength 1054 nm of the light beam.

  Further, the thickness of the metal film 6 at each wavelength of the light beam 13 emitted from the light source 2 is such that the minimum value Rmin of the reflectance is close to 0, and the metal film 6 when the wavelength of the light beam 13 is 635 nm. When the wavelength of the light beam 13 is 780 nm, the thickness of the metal film 6 is 45 nm. When the wavelength of the light beam 13 is 1054 nm, the thickness of the metal film 6 is 40 nm.

  As shown in FIG. 8, the full width at half maximum of dip in which the reflectance at each wavelength of the light beam 13 falls is about 1.2 degrees when the wavelength of the light beam 13 is 635 nm, and about 0 when the wavelength of the light beam 13 is 780 nm. It can be seen that when the wavelength of the light beam 13 is 1054 nm, it is about 0.12 degrees.

  Next, selection of the film thickness of the metal film 6 at each wavelength of the light source 2 when the extinction coefficient is increased from 0 in consideration of the light absorption of the sample 14 will be described.

[Wavelength 635nm]
First, when the wavelength of the light beam 13 is 635 nm, the relationship between the extinction coefficient of the sample 14, the incident angle θmin, and the reflectance Rmin when the thickness of the metal film 6 is 33.5 nm, 40 nm, and 50 nm. Will be described with reference to FIGS. 9A and 9B. FIG. 9A is a graph showing the relationship between the extinction coefficient of the sample 14 and the incident angle θmin when the wavelength of the light beam is 635 nm, and FIG. 9B shows the relationship between the wavelength of the light beam of 635 nm. It is the graph which showed the relationship between the extinction coefficient of the sample 14, and reflectance Rmin in the case. The dotted line indicates the film thickness of 33.5 nm, the broken line indicates the film thickness of 40 nm, and the solid line indicates the film thickness of 50 nm.

  When the thickness of the metal film 6 is 50 nm, which is the thickness d of the wavelength 635 nm of the light beam 13, the incident angle increases as the extinction coefficient increases from 0 to 0.035 as shown in FIG. It can be seen that θmin increases by about 0.2 degrees. The increased value of the incident angle θmin is about 1/6 of the full width at half maximum (about 1.2 degrees) of the dip described above, and is a range that is detected as an error. The error of the incident angle θmin is detected with the refractive index of the sample 14 not including the detection target as 1.003. Also, the value of the reflectance Rmin increases as the extinction coefficient increases, as shown in FIG. 9B. This is a reduction in S / N at the time of detecting the incident angle θmin.

  When the thickness of the metal film 6 is 40 nm, as shown in FIG. 9A, the incident angle θmin increases by about 0.13 degrees as the extinction coefficient increases from 0 to 0.035. This is about 1/10 of the full width at half maximum (about 1.2 degrees) of dip described above, and is an angle shift that cannot be detected. Further, as shown in FIG. 9B, the value of the reflectance Rmin is also suppressed to a fluctuation of about half compared with the case of 50 nm.

  Further, when the thickness of the metal film 6 is 33.5 nm, as shown in FIGS. 9A and 9B, the incident angle θmin and the reflectance Rmin are the same as the case where the thickness d is 50 nm. It turns out that it is a change of a grade.

  From the above, when the wavelength of the light beam 13 is 635 nm, the change of the incident angle θmin is suppressed to about 1/10 of the full width at half maximum of dip when the thickness of the metal film 6 is 50 nm which is the film thickness d. Shows that there is a problem that only the sample 14 having an extinction coefficient in the range of 0 to 0.024 can be measured. However, the influence of the absorption of the sample 14 on the incident angle θmin can be reduced by setting the thickness of the metal film 6 to 40 nm, that is, a thickness thinner than the thickness d. However, if the thickness of the metal film 6 is reduced to 33.5 nm, the same problem as when the thickness of the metal film 6 is set to the film thickness d occurs.

  Therefore, when the wavelength of the light beam 13 is 635 nm, the film thickness of the metal film 6 is reduced within the range of about 0 nm to about 16.5 nm with respect to the film thickness d of the metal film 6. It can be seen that the incident angle θmin and the reflectance Rmin with respect to the metal film 6 are less affected by the change in the extinction coefficient than when the film thickness of the metal film 6 is set to the film thickness d.

[Wavelength 780nm]
Next, when the wavelength of the light beam 13 is 780 nm, the extinction coefficient of the sample 14, the incident angle θmin, and the reflectance Rmin when the film thickness of the metal film 6 is 26.5 nm, 30 nm, and 45 nm are given. The relationship will be described with reference to FIG. FIG. 10A is a graph showing the relationship between the extinction coefficient of the sample 14 and the incident angle θmin when the wavelength of the light beam is 780 nm, and FIG. 10B shows the relationship between the wavelength of the light beam of 780 nm. It is the graph which showed the relationship between the extinction coefficient of the sample 14, and reflectance Rmin in the case. Note that the dotted line indicates a film thickness of 26.5 nm, the broken line indicates a film thickness of 30 nm, and the solid line indicates a film thickness of 45 nm.

  When the thickness of the metal film 6 is 45 nm, which is the thickness d of the wavelength of the light beam 13, the incident angle increases as the extinction coefficient increases from 0 to 0.018 as shown in FIG. It can be seen that θmin increases by about 0.07 degrees. The increased value of the incident angle θmin is about 1/3 of the full width at half maximum (about 0.3 degrees) of the above-described dip, and is a range that is detected as an error. The error of the incident angle θmin is detected with the refractive index of the sample 14 not including the detection target as 1.002. Further, the value of the reflectance Rmin also increases as the extinction coefficient increases as shown in FIG. This is a reduction in S / N at the time of detecting the incident angle θmin.

  When the thickness of the metal film 6 is 30 nm, the incident angle θmin increases by about 0.04 degrees as the extinction coefficient increases from 0 to 0.018 as shown in FIG. . This is about 1/10 of the full width at half maximum of dip (about 0.3 degrees) described above, and is an angle shift that cannot be detected. As shown in FIG. 10B, the value of the reflectance Rmin is also suppressed to a fluctuation of about 1/3 compared to the case of 45 nm.

  Further, when the thickness of the metal film 6 is 26.5 nm, as shown in FIGS. 10A and 10B, the incident angle θmin and the reflectance Rmin are the same as when the film thickness d is 45 nm. It turns out that it is a change of a grade.

  From the above, when the wavelength of the light beam 13 is 780 nm, in order to suppress the change in the incident angle θmin to about 1/10 of the full width at half maximum of dip when the thickness of the metal film 6 is 45 nm which is the film thickness d. Indicates that there is a problem that only the sample 14 having an extinction coefficient in the range of 0 to 0.01 can be measured. However, the influence of the absorption of the sample 14 on the incident angle θmin can be reduced by setting the thickness of the metal film 6 to 30 nm, that is, a thickness thinner than the thickness d. However, if the thickness of the metal film 6 is reduced to 26.5 nm, the same problem as when the thickness of the metal film 6 is set to the film thickness d occurs.

  Therefore, when the wavelength of the light beam 13 is 780 nm, the film thickness of the metal film 6 is reduced within the range of about 0 nm to about 18.5 nm with respect to the film thickness d of the metal film 6. It can be seen that the incident angle θmin and the reflectance Rmin with respect to the metal film 6 are less affected by the change in the extinction coefficient than when the film thickness of the metal film 6 is set to the film thickness d.

[Wavelength 1054nm]
Next, when the wavelength of the light beam 13 is 1054 nm, the relationship between the extinction coefficient of the sample 14, the incident angle θmin, and the reflectance Rmin when the thickness of the metal film 6 is 22 nm, 25 nm, and 40 nm. This will be described with reference to FIG. FIG. 11A is a graph showing the relationship between the extinction coefficient of the sample 14 and the incident angle θmin when the wavelength of the light beam is 1054 nm. FIG. 11B shows the relationship between the light beam wavelength of 1054 nm. It is the graph which showed the relationship between the extinction coefficient of the sample 14, and reflectance Rmin in the case. In addition, when a dotted line has a film thickness of 22 nm, a broken line has a film thickness of 25 nm, and a solid line has a film thickness of 40 nm.

  When the thickness of the metal film 6 is 40 nm, which is the thickness d of the wavelength of the light beam 13, the incident angle increases as the extinction coefficient increases from 0 to 0.007 as shown in FIG. It can be seen that θmin increases by about 0.03 degrees. The increased value of the incident angle θmin is about ¼ of the full width at half maximum (about 0.12 degrees) of the dip described above, and is a range that is detected as an error. This error in the incident angle θmin is detected with the refractive index of the sample 14 not including the detection target as 1.001. Further, the value of the reflectance Rmin also increases as the extinction coefficient increases as shown in FIG. This is a reduction in S / N at the time of detecting the incident angle θmin.

  When the thickness of the metal film 6 is 25 nm, the increment of the incident angle θmin when the extinction coefficient increases from 0 to 0.007 is about 0.015 degrees. This is an angle shift that is about 1/10 of the full width at half maximum of dip and cannot be detected. Further, the reflectance Rmin when the extinction coefficient increases is also suppressed to a fluctuation of about 1/3 compared to the case of 35 nm.

  When the film thickness of the metal film 6 is 22 nm, as shown in FIGS. 11A and 11B, the incident angle θmin and the reflectance Rmin are about the same as those when the film thickness d is 40 nm. It turns out that it is a change.

  From the above, when the wavelength of the light beam 13 is 1054 nm, the change in the incident angle θmin is suppressed to about 1/10 of the full width at half maximum of dip when the thickness of the metal film 6 is set to 40 nm which is the film thickness d. Shows that there is a problem that only the sample 14 having an extinction coefficient in the range of 0 to 0.003 can be measured. However, the influence of the absorption of the sample 14 on the incident angle θmin can be reduced by setting the thickness of the metal film 6 to 25 nm, that is, a thickness thinner than the thickness d. However, if the thickness of the metal film 6 is reduced to 22 nm, the same problem as when the thickness of the metal film 6 is set to the thickness d is caused.

  Therefore, when the wavelength of the light beam 13 is 1054 nm, the thickness of the metal film 6 is reduced within the range of about 0 nm to about 18 nm with respect to the thickness d of the metal film 6. It can be seen that the incident angle θmin and the reflectance Rmin with respect to the film 6 are less influenced by changes in the extinction coefficient than when the thickness of the metal film 6 is set to the film thickness d.

[Third embodiment]
Next, a third embodiment for selecting the thickness of the metal film 6 will be described with reference to FIGS. In the present embodiment, as the above four elements, Au is used as the material of the metal film 6, three wavelengths of 635 nm, 780 nm, and 1054 nm are used as the wavelength of the light source 2, and 1.46 is detected as the refractive index of the prism 5. The selection of the film thickness of the metal film 6 in the case where 1.0 is selected as the refractive index in a state not including the target will be described.

  First, the relationship between the incident angle of the light beam 13 with respect to the metal film 6 and the reflectance at each wavelength of the light source 2 when the extinction coefficient is set to 0 with the above four elements will be described with reference to FIG. FIG. 12 shows the relationship between the incident angle and the reflectance of the light beam 13 having the wavelengths of 635 nm, 780 nm, and 1054 nm emitted from the light source 2 when the extinction coefficient is 0 for the above four elements. It is a graph to show. In the figure, the dotted line indicates the wavelength 635 nm of the light beam 13, the broken line indicates the wavelength 780 nm of the light beam, and the solid line indicates the wavelength 1054 nm of the light beam.

  Further, the thickness of the metal film 6 at each wavelength of the light beam 13 emitted from the light source 2 is such that the minimum value Rmin of the reflectance is close to 0, and the metal film 6 when the wavelength of the light beam 13 is 635 nm. When the wavelength of the light beam 13 is 780 nm, the thickness of the metal film 6 is 45 nm. When the wavelength of the light beam 13 is 1054 nm, the thickness of the metal film 6 is 40 nm.

  As shown in FIG. 12, the full width at half maximum of dip in which the reflectance at each wavelength of the light beam 13 falls is about 2.1 degrees when the wavelength of the light beam 13 is 635 nm and about 0 when the wavelength of the light beam 13 is 780 nm. It can be seen that when the wavelength of the light beam 13 is 1054 nm, it is about 0.18 degree.

  Next, selection of the film thickness of the metal film 6 at each wavelength of the light source 2 when the extinction coefficient is increased from 0 in consideration of the light absorption of the sample 14 will be described.

[Wavelength 635nm]
First, when the wavelength of the light beam 13 is 635 nm, the relationship between the extinction coefficient of the sample 14, the incident angle θmin, and the reflectance Rmin when the thickness of the metal film 6 is 33 nm, 40 nm, and 50 nm is shown. This will be described with reference to FIG. 13 (a) and FIG. 13 (b). FIG. 13A is a graph showing the relationship between the extinction coefficient of the sample 14 and the incident angle θmin when the wavelength of the light beam is 635 nm, and FIG. 13B shows the relationship between the wavelength of the light beam of 635 nm. It is the graph which showed the relationship between the extinction coefficient of the sample 14, and reflectance Rmin in the case. A dotted line indicates a film thickness of 33 nm, a broken line indicates a film thickness of 40 nm, and a solid line indicates a film thickness of 50 nm.

  When the thickness of the metal film 6 is 50 nm, which is the thickness d of the wavelength 635 nm of the light beam 13, the incident angle increases as the extinction coefficient increases from 0 to 0.032 as shown in FIG. It can be seen that θmin increases by about 0.33 degrees. The increased value of the incident angle θmin is about 1/6 of the full width at half maximum (about 2.1 degrees) of dip described above, and is a range that is detected as an error. The error of the incident angle θmin is detected with the refractive index of the sample 14 not including the detection target being 1.005. Further, the value of the reflectance Rmin also increases as the extinction coefficient increases, as shown in FIG. This is a reduction in S / N at the time of detecting the incident angle θmin.

  When the thickness of the metal film 6 is 40 nm, as shown in FIG. 13A, the incident angle θmin increases by about 0.2 degrees as the extinction coefficient increases from 0 to 0.032. This is about 1/10 of the full width at half maximum (about 2.1 degrees) of dip described above, and is an angle shift that cannot be detected. Further, as shown in FIG. 13B, the value of the reflectance Rmin is also suppressed to a fluctuation of about half compared with the case of 50 nm.

  When the film thickness of the metal film 6 is 33 nm, as shown in FIGS. 13A and 13B, the incident angle θmin and the reflectance Rmin are approximately the same as the case where the film thickness d is 50 nm. It turns out that it is a change.

  From the above, when the wavelength of the light beam 13 is 635 nm, the change of the incident angle θmin is suppressed to about 1/10 of the full width at half maximum of dip when the thickness of the metal film 6 is 50 nm which is the film thickness d. Shows that there is a problem that only the sample 14 having an extinction coefficient in the range of 0 to 0.024 can be measured. However, the influence of the absorption of the sample 14 on the incident angle θmin can be reduced by setting the thickness of the metal film 6 to 40 nm, that is, a thickness thinner than the thickness d. However, if the thickness of the metal film 6 is reduced to 33 nm, the same problem as when the thickness of the metal film 6 is set to the film thickness d is caused.

  Therefore, when the wavelength of the light beam 13 is 635 nm, the thickness of the metal film 6 is reduced within the range of about 0 nm to about 17 nm with respect to the thickness d of the metal film 6. It can be seen that the incident angle θmin and the reflectance Rmin with respect to the film 6 are less influenced by changes in the extinction coefficient than when the thickness of the metal film 6 is set to the film thickness d.

[Wavelength 780nm]
Next, when the wavelength of the light beam 13 is 780 nm, the relationship between the extinction coefficient of the sample 14, the incident angle θmin, and the reflectance Rmin when the thickness of the metal film 6 is 27 nm, 30 nm, and 45 nm. This will be described with reference to FIG. FIG. 14A is a graph showing the relationship between the extinction coefficient of the sample 14 and the incident angle θmin when the wavelength of the light beam is 780 nm, and FIG. 14B shows the relationship between the wavelength of the light beam of 780 nm. It is the graph which showed the relationship between the extinction coefficient of the sample 14, and reflectance Rmin in the case. In addition, the case where the dotted line is a film thickness of 27 nm, the broken line is the film thickness of 30 nm, and the solid line is the film thickness of 45 nm is shown.

  When the thickness of the metal film 6 is 45 nm, which is the thickness d of the wavelength of the light beam 13, the incident angle increases as the extinction coefficient increases from 0 to 0.015 as shown in FIG. It can be seen that θmin increases by about 0.08 degrees. The increased value of the incident angle θmin is about 1/5 of the full width at half maximum (about 0.4 degrees) of the dip described above, and is a range that is detected as an error. The error of the incident angle θmin is detected as a refractive index of 1.0015 in a state where the sample 14 does not include the detection target. Also, the value of the reflectance Rmin increases as the extinction coefficient increases, as shown in FIG. This is a reduction in S / N at the time of detecting the incident angle θmin.

  When the thickness of the metal film 6 is 30 nm, as shown in FIG. 14A, the incident angle θmin increases by about 0.04 degrees as the extinction coefficient increases from 0 to 0.015. . This is about 1/10 of the full width at half maximum of the dip (about 0.4 degrees) described above, and is an angle shift that cannot be detected. As shown in FIG. 14B, the value of the reflectance Rmin is also suppressed to a fluctuation of about half compared to the case of 45 nm.

  Further, when the film thickness of the metal film 6 is 27 nm, as shown in FIGS. 14A and 14B, the incident angle θmin and the reflectance Rmin are about the same as those in the case where the film thickness d is 45 nm. It turns out that it is a change.

  From the above, when the wavelength of the light beam 13 is 780 nm, in order to suppress the change in the incident angle θmin to about 1/10 of the full width at half maximum of dip when the thickness of the metal film 6 is 45 nm which is the film thickness d Shows that there is a problem that only the sample 14 having an extinction coefficient in the range of 0 to 0.008 can be measured. However, the influence of the absorption of the sample 14 on the incident angle θmin can be reduced by setting the thickness of the metal film 6 to 30 nm, that is, a thickness thinner than the thickness d. However, if the thickness of the metal film 6 is reduced to 27 nm, the same problem as when the thickness of the metal film 6 is set to the thickness d is caused.

  Therefore, when the wavelength of the light beam 13 is 780 nm, the thickness of the metal film 6 is reduced within the range of about 0 nm to about 18 nm with respect to the film thickness d of the metal film 6. It can be seen that the incident angle θmin and the reflectance Rmin with respect to the film 6 are less influenced by changes in the extinction coefficient than when the thickness of the metal film 6 is set to the film thickness d.

[Wavelength 1054nm]
Next, when the wavelength of the light beam 13 is 1054 nm, the relationship between the extinction coefficient of the sample 14, the incident angle θmin, and the reflectance Rmin when the thickness of the metal film 6 is 21 nm, 25 nm, and 40 nm. This will be described with reference to FIG. FIG. 15A is a graph showing the relationship between the extinction coefficient of the sample 14 and the incident angle θmin when the wavelength of the light beam is 1054 nm, and FIG. 15B shows the relationship between the wavelength of the light beam of 1054 nm. It is the graph which showed the relationship between the extinction coefficient of the sample 14, and reflectance Rmin in the case. In addition, the case where the dotted line is a film thickness of 21 nm, the broken line is the film thickness of 25 nm, and the solid line is the film thickness of 40 nm is shown.

  When the thickness of the metal film 6 is 40 nm, which is the thickness d of the wavelength of the light beam 13, the incident angle increases as the extinction coefficient increases from 0 to 0.007 as shown in FIG. It can be seen that θmin increases by about 0.05 degrees. The increased value of the incident angle θmin is about ¼ of the full width at half maximum (about 0.18 degrees) of dip described above, and is a range that is detected as an error. This error in the incident angle θmin is detected with the refractive index of the sample 14 not including the detection target as 1.001. Further, the value of the reflectance Rmin also increases as the extinction coefficient increases as shown in FIG. This is a reduction in S / N at the time of detecting the incident angle θmin.

  When the thickness of the metal film 6 is 25 nm, the increment of the incident angle θmin when the extinction coefficient increases from 0 to 0.007 is about 0.02 degrees. This is an angle shift that is about 1/10 of the full width at half maximum of dip and cannot be detected. Further, the reflectance Rmin when the extinction coefficient is increased is also suppressed to about half of the fluctuation compared to the case of 40 nm.

  Further, when the film thickness of the metal film 6 is 21 nm, as shown in FIGS. 15A and 15B, the incident angle θmin and the reflectance Rmin are about the same as those when the film thickness d is 40 nm. It turns out that it is a change.

  From the above, when the wavelength of the light beam 13 is 1054 nm, the change in the incident angle θmin is suppressed to about 1/10 of the full width at half maximum of dip when the thickness of the metal film 6 is set to 40 nm which is the film thickness d. Shows that there is a problem that only the sample 14 having an extinction coefficient in the range of 0 to 0.003 can be measured. However, the influence of the absorption of the sample 14 on the incident angle θmin can be reduced by setting the thickness of the metal film 6 to 25 nm, that is, a thickness thinner than the thickness d. However, if the thickness of the metal film 6 is reduced to 21 nm, the same problem as when the thickness of the metal film 6 is set to the film thickness d is caused.

  Therefore, when the wavelength of the light beam 13 is 1054 nm, the thickness of the metal film 6 is reduced within the range of about 0 nm to about 19 nm with respect to the thickness d of the metal film 6. It can be seen that the incident angle θmin and the reflectance Rmin with respect to the film 6 are less influenced by changes in the extinction coefficient than when the thickness of the metal film 6 is set to the film thickness d.

  As shown in the first to third embodiments, when the film thickness of the metal film 6 is the film thickness d, that is, the film thickness causing the surface plasmon resonance with the extinction coefficient being 0, When the extinction coefficient is 0, the incident angle θmin and the reflectance Rmin are minimum values. That is, the incident angle θmin and the reflectance Rmin are minimum values when the extinction coefficient is 0, and monotonously increase as the extinction coefficient increases. Therefore, in order to suppress changes in the incident angle θmin and the reflectance Rmin within a predetermined range, there arises a problem that only a detection target of an extinction coefficient in a narrow range can be measured.

  Therefore, in the surface plasmon sensor 1, by making the film thickness of the metal film 6 smaller than the film thickness d, the incident angle θmin and the reflectance Rmin can be minimized with a predetermined extinction coefficient value. That is, the incident angle θmin and the reflectance Rmin decrease once when the extinction coefficient is 0 to a predetermined value and increase after the predetermined value. Therefore, compared with the case where the film thickness of the metal film 6 is set to the film thickness d, the change of the incident angle θmin and the reflectance Rmin can be reduced to about half.

  At this time, the lower limit value of the film thickness of the metal film 6 is a film thickness at which the incident angle θmin is the same as the incident angle θmin when the film thickness of the metal film 6 is the film thickness d. That is, the effect of the present invention described above can be obtained by setting the film thickness of the metal film 6 within the range from the lower limit value to the film thickness d. Based on the results of the first to third embodiments in the method of selecting the thickness of the metal film 6, the thickness d, the recommended thickness, and the lower limit value of the metal film 6 are summarized in the following table. (Unit is nm)

  From Table 1 above, it can be seen that the effect of the present invention can be obtained if the thickness of the metal film 6 is in the range from the thickness 20 nm thinner than the thickness d to the thickness d. Thus, by making the difference between the film thickness d and the film thickness d of the metal film 6 approximately 20 nm or less, the variation in the incident angle θmin accompanying the increase in the extinction coefficient can be suppressed more than in the case of the film thickness d. it can. In addition, since the fluctuation of the reflectance Rmin can also be suppressed as compared with the case of the film thickness d, it is possible to suppress the deterioration of S / N when the incident angle θmin is detected.

  It can also be seen that the recommended value range can be obtained by making the metal film 6 thinner than the film thickness d in the range of 10 nm to 15 nm. Thereby, the fluctuation of the incident angle θmin accompanying the increase in the extinction coefficient can be sufficiently reduced, for example, to about 1/10 of dip. Therefore, it is possible to maximize the range of the extinction coefficient of the detection target in which the accurate refractive index of the sample 14 can be detected. In addition, since the fluctuation of the reflectance Rmin in the range of the extinction coefficient can be suppressed to less than half compared with the case where the film thickness of the metal film 6 is set to the film thickness d, the S / N at the time of detecting the incident angle θmin. Can be prevented.

  Therefore, by making the film thickness of the metal film 6 thinner than the film thickness d, the change in the incident angle θmin depends only on the refractive index of the sample 14 even when the sample 14 has absorption. Therefore, the calculation circuit 11 can calculate an accurate refractive index and further a density corresponding to the incident angle θmin from the relationship between the incident angle θmin inputted in advance and the refractive index of the sample 14.

  Here, the relationship among the incident angle θmin, the reflectance Rmin, and the refractive index will be described with reference to FIG. FIG. 16A uses Au as the material of the metal film 6, 2.0 as the refractive index of the prism 5, 1.33 as the refractive index when the sample 14 does not include the detection target, and an extinction coefficient of 0 16 is a graph in which the relationship between the incident angle θmin and the refractive index of the sample 14 is plotted. FIG. 16B shows Au as the material of the metal film 6, 2.0 as the refractive index of the prism 5, and the sample. 14 is a graph in which the relationship between the reflectance Rmin and the refractive index of the sample 14 is plotted when 1.33 is used as the refractive index in a state that does not include 14 detection targets and the extinction coefficient is 0.

  From the graph of FIG. 16A, it can be seen that the relationship between the incident angle θmin and the refractive index of the sample 14 is substantially linear. Further, even when other combinations are used as the material of the metal film 6, the refractive index of the prism 5, and the refractive index in a state not including the detection target of the sample 14, it is the same as the graph shown in FIG. Becomes linear. Therefore, the calculation circuit 11 calculates the refractive index of the sample 14 from the incident angle θmin by a very simple calculation by calculating the relationship between the incident angle θmin and the refractive index of the sample 14 in advance and performing linear approximation. Can be calculated. Further, since the relationship between the refractive index and the concentration of the sample 14 is almost linear, the concentration can be calculated by a simple calculation as in the relationship between the incident angle θmin and the refractive index.

  Moreover, it can be seen from the graph of FIG. 16B that the refractive index of the sample 14 does not depend on the reflectance Rmin. Therefore, the refractive index of the sample 14 can be calculated based only on the incident angle θmin.

  In order to further reduce the error in detecting the refractive index of the sample 14, it is desirable to select the thickness of the metal film 6 according to the range of the extinction coefficient of the sample 14. Specifically, when the extinction coefficient of the sample 14 is smaller than the range described in the first to third embodiments, the film thickness is made closer to the film thickness d.

  In the above description, if the change in the incident angle θmin is about 1/10 of the full width at half maximum of dip, it has been described that the angle shift is in a range that cannot be detected. However, the detection sensitivity of the surface plasmon sensor 1 is increased. Accordingly, it is desirable to make the thickness of the metal film 6 closer to the thickness d.

  In the first to third embodiments of the method for selecting the thickness of the metal film 6, Au is used as the material of the metal film 6, but the principle of the present invention is that the metal film 6 The present invention is not limited to the case where it is made of Au, and can be applied even when the metal film 6 is made of another material. Also, the prism 5 and the sample 14 are the same as the metal film 6, and the principle of the present invention can be applied even if the prism 5 and the sample 14 are made of materials other than those described above.

  Further, even when the liquid or gas itself that does not include the detection target, which is the sample 14, has absorption, the detection target is absorbed, and when the concentration of the liquid or gas including the detection target is increased, the sample 14 is turned off. If the attenuation coefficient increases, the principle of the present invention is the same.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  The present invention detects the refractive index of a liquid or gas containing a detection target, and is suitably used for measuring the concentration of the liquid or gas, detecting proteins or polymers, and the like.

It is a figure which shows the outline of the whole structure of one Embodiment of the surface plasmon sensor which concerns on this invention. It is a figure which shows one Example of the contact method of the sample with respect to the metal film of a surface plasmon sensor. It is a figure which shows another Example of the contact method of the sample with respect to the metal film of a surface plasmon sensor. When the metal film is made of Au, the refractive index of the prism is 2.0, the refractive index of the sample is 1.33, and the extinction coefficient is 0, the wavelengths emitted from the light source are 635 nm, 780 nm, It is a graph which shows the relationship between the incident angle with respect to the metal film of a 1054 nm light beam, and a reflectance. (A) is a graph showing the relationship between the extinction coefficient of the sample and the incident angle θmin when the wavelength of the light beam is 635 nm, and (b) is a graph of the sample when the wavelength of the light beam is 635 nm. It is the graph which showed the relationship between an extinction coefficient and reflectance Rmin. (A) is a graph showing the relationship between the extinction coefficient of the sample and the incident angle θmin when the wavelength of the light beam is 780 nm, and (b) is a graph of the sample when the wavelength of the light beam is 780 nm. It is the graph which showed the relationship between an extinction coefficient and reflectance Rmin. (A) is a graph showing the relationship between the extinction coefficient of the sample and the incident angle θmin when the wavelength of the light beam is 1054 nm, and (b) is a graph of the sample when the wavelength of the light beam is 1054 nm. It is the graph which showed the relationship between an extinction coefficient and reflectance Rmin. When the metal film material is Au, the prism refractive index is 2.0, the sample refractive index is 1.0, and the extinction coefficient is 0, the wavelengths emitted from the light source are 635 nm, 780 nm, It is a graph which shows the relationship between the incident angle with respect to the metal film of a 1054 nm light beam, and a reflectance. (A) is a graph showing the relationship between the extinction coefficient of the sample and the incident angle θmin when the wavelength of the light beam is 635 nm, and (b) is a graph of the sample when the wavelength of the light beam is 635 nm. It is the graph which showed the relationship between an extinction coefficient and reflectance Rmin. (A) is a graph showing the relationship between the extinction coefficient of the sample and the incident angle θmin when the wavelength of the light beam is 780 nm, and (b) is a graph of the sample when the wavelength of the light beam is 780 nm. It is the graph which showed the relationship between an extinction coefficient and reflectance Rmin. (A) is a graph showing the relationship between the extinction coefficient of the sample and the incident angle θmin when the wavelength of the light beam is 1054 nm, and (b) is a graph of the sample when the wavelength of the light beam is 1054 nm. It is the graph which showed the relationship between an extinction coefficient and reflectance Rmin. When the metal film is made of Au, the refractive index of the prism is 1.46, the refractive index of the sample is 1.0, and the extinction coefficient is 0, the wavelengths emitted from the light source are 635 nm, 780 nm, It is a graph which shows the relationship between the incident angle with respect to the metal film of a 1054 nm light beam, and a reflectance. (A) is a graph showing the relationship between the extinction coefficient of the sample and the incident angle θmin when the wavelength of the light beam is 635 nm, and (b) is a graph of the sample when the wavelength of the light beam is 635 nm. It is the graph which showed the relationship between an extinction coefficient and reflectance Rmin. (A) is a graph showing the relationship between the extinction coefficient of the sample and the incident angle θmin when the wavelength of the light beam is 780 nm, and (b) is a graph of the sample when the wavelength of the light beam is 780 nm. It is the graph which showed the relationship between an extinction coefficient and reflectance Rmin. (A) is a graph showing the relationship between the extinction coefficient of the sample and the incident angle θmin when the wavelength of the light beam is 1054 nm, and (b) is a graph of the sample when the wavelength of the light beam is 1054 nm. It is the graph which showed the relationship between an extinction coefficient and reflectance Rmin. (A) shows the incident angle θmin and the refractive index of the sample when Au is used as the material of the metal film, 2.0 is used as the refractive index of the prism, 1.33 is used as the refractive index of the sample, and the extinction coefficient is 0. (B) is a graph in which Au is used as the material of the metal film, 2.0 is used as the refractive index of the prism, 1.33 is used as the refractive index of the sample, and the extinction coefficient is 0. Is a graph plotting the relationship between the reflectance Rmin and the refractive index of the sample.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Surface plasmon sensor 2 Light source 3 Collimate lens 4 Condensing lens 5 Prism (dielectric substrate)
6 Metal film 7 First lens 8 Second lens 9 Light detector 10 Light source drive circuit 11 Calculation circuit 12 Monitor 13 Light beam 14 Sample (liquid or gas including detection target)
15 Flow cell

Claims (2)

A dielectric substrate having translucency;
A metal film formed on the dielectric substrate and made of gold in contact with a liquid or gas containing a detection target, wherein an adsorption layer that adsorbs a predetermined molecule is formed on the surface of the metal film;
A surface plasmon sensor for detecting a refractive index of the liquid or the gas, comprising: a light source that irradiates a light beam on a surface of the metal film opposite to a surface in contact with the liquid or the gas in the metal film. In
The dielectric substrate is detachable from the surface plasmon sensor,
The wavelength of the light beam is 1054 nm to 1550 nm,
The film thickness of the metal film is smaller than the film thickness d at which the minimum reflectance of the light beam with respect to the metal film in contact with the liquid or the gas not including the detection target is minimized, and further, the metal The surface plasmon sensor characterized in that the difference between the film thickness and the film thickness d is 10 nm to 15 nm.   The reflectance of the light beam decreases when the extinction coefficient of the liquid or gas including the detection target is in the range of 0 to a predetermined value, and the reflectance increases after the predetermined value, thereby absorbing light. The surface plasmon sensor according to claim 1, wherein a refractive index of a detection target is detected.

Images