Detection device

Abstract

To provide a detection device capable of simplifying the whole device while improving degree of freedom of optical design.SOLUTION: A detection device 1 using surface plasmon resonance comprises: a light source 2; a sensor part 3 including an optical prism 5 including a light incident surface 5a, a bottom surface 5b and a light emission surface 5c, and a thin metallic film 6 provided on the bottom surface 5b of the optical prism 5 and reflecting light emitted from the light source 2 and entering the light incident surface 5a toward the light emission surface 5c; and a detector 4 detecting light reflected on the thin metallic film 6 of the sensor part 3. The optical prism 5 is made of glass with a refractive index nd of 1.9 or more and 3.0 or less. An angle formed between the light incident surface 5a and the light emission surface 5c of the optical prism 5 is 140° or more and less than 180°. An optical axis X connecting the light source 2 and the detector 4 is substantially parallel to the bottom surface 5b of the optical prism 5.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a detection device that utilizes surface plasmon resonance. [Background technology]

[0002] Conventionally, detection devices utilizing surface plasmon resonance have been known. Because the resonance conditions of surface plasmons are sensitive to the presence or absence of a substance near the surface and the refractive index, detection devices utilizing surface plasmon resonance can be used as highly sensitive means for detecting substances. For example, detection devices utilizing surface plasmons can measure minute changes in the refractive index of a measurement object, and are therefore used in fields such as refractive index sensors, biosensors, and chemical sensors.

[0003] The following Patent Document 1 discloses a detection device equipped with a sensor unit having a prism and a flat plate provided below the prism and having a metal film attached to its bottom surface. Patent Document 1 describes that by utilizing surface plasmon resonance that occurs when light incident on the prism is totally reflected at the interface between the flat plate and the metal film, changes in the refractive index of a measurement object placed on the surface of the metal film can be measured, and intracellular protein interactions such as immune reactions can be measured. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-191053 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, a detection device using surface plasmons usually requires a mechanical mechanism that precisely controls the angle of incidence and the angle of reflection using a rotary stage or the like, and therefore there is a demand for simplification and miniaturization of the entire device. On the other hand, a detection device such as that described in Patent Document 1 has a problem in that it is difficult to increase the degree of freedom in optical design while simplifying the entire device.

[0006] An object of the present invention is to provide a detection device that can simplify the entire device while increasing the degree of freedom in optical design. [Means for solving the problem]

[0007] Hereinafter, various aspects of the detection device that solve the above problems will be described.

[0008] A detection device according to a first aspect of the present invention is a detection device that utilizes surface plasmon resonance, comprising: a light source; an optical prism having a light incident surface, a bottom surface, and a light exit surface; a sensor unit provided on the bottom surface of the optical prism and having a metal thin film that reflects light emitted from the light source and incident on the light incident surface toward the light exit surface; and a detector that detects the light reflected by the metal thin film of the sensor unit, wherein the optical prism is made of glass having a refractive index nd of 1.9 or more and 3.0 or less, an angle between the light incident surface and the light exit surface of the optical prism is 140° or more and less than 180°, and an optical axis connecting the light source and the detector is approximately parallel to the bottom surface of the optical prism. Note that the light incident surface refers to the surface on which light enters the optical prism from the outside, and the light exit surface refers to the surface on which light exits the optical prism to the outside.

[0009] In the detection device according to aspect 2, in accordance with aspect 1, it is preferable that the wavelength of the light emitted from the light source is not less than 600 nm and not more than 1500 nm.

[0010] In the detection device according to the third aspect, in the first or second aspect, it is preferable that the light emitted from the light source is incoherent light.

[0011] In the detection device according to aspect 4, in any one of aspects 1 to 3, it is preferable that the ratio of the height of the optical axis from the bottom surface of the optical prism is 0.4 or more.

[0012] In the detection device according to aspect 5, in any one of aspects 1 to 4, it is preferable that the beam diameter of the light emitted from the light source is 1 mm or more.

[0013] In the detection device according to Aspect 6, in any one of Aspects 1 to 5, the refractive index sensitivity is preferably 1000 nm / RIU or more and 30000 nm / RIU or less. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a detection device that can simplify the entire device while increasing the degree of freedom in optical design. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a detection device according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view showing a sensor unit constituting a detection device according to one embodiment of the present invention. [Figure 3] FIG. 3 is a schematic diagram illustrating the optical path when the refractive index nd of the glass constituting the optical prism is set to 2.0 in a detection device according to one embodiment of the present invention. [Figure 4] FIG. 4 is a diagram showing the relationship between the inner incident angle θ2 and reflectance when the wavelength of light emitted from the light source is 633 nm and the refractive index nd of the glass constituting the optical prism is 2.0 in a detection device according to one embodiment of the present invention. [Figure 5]FIG. 5 is a diagram showing the relationship between the outer incident angle θ1 and the inner incident angle θ2 when the refractive index nd of the glass constituting the optical prism is 2.0 and the apex angle α of the optical prism is 90° in a detection device according to one embodiment of the present invention. [Figure 6] FIG. 6 is a diagram showing the relationship between the outer incident angle θ1 and the inner incident angle θ2 when the refractive index nd of the glass constituting the optical prism is 2.0 and the apex angle α of the optical prism is 120° in a detection device according to one embodiment of the present invention. [Figure 7] FIG. 7 is a diagram showing the relationship between the outer incident angle θ1 and the inner incident angle θ2 when the refractive index nd of the glass constituting the optical prism is 2.0 and the apex angle α of the optical prism is 140° in a detection device according to one embodiment of the present invention. [Figure 8] FIG. 8 is a diagram showing the relationship between the apex angle α of the optical prism and the ratio of the height h of the optical axis from the bottom surface to the height H of the optical prism, and the white circles in the diagram indicate the optimal apex angle as a sensor for each refractive index nd. [Figure 9] FIG. 9 is a diagram showing the relationship between the wavelength of incident light and reflectance when the refractive index nd of the glass constituting the optical prism in a detection device according to one embodiment of the present invention is set to 2.0. In the diagram, the dashed line represents the case where the refractive index nd of the surrounding medium is 1.33, and the solid line represents the case where the refractive index nd of the surrounding medium is 1.34. [Figure 10] FIG. 10 is a diagram showing the relationship between the apex angle α and the refractive index sensitivity when the refractive index nd of the glass constituting the optical prism is set to 2.0 in a detection device according to one embodiment of the present invention. [Figure 11] FIG. 11 is a diagram showing the relationship between the wavelength of incident light and reflectance when the refractive index nd of the glass constituting the optical prism in a detection device according to one embodiment of the present invention is set to 1.9. In the diagram, the dashed line represents the case where the refractive index nd of the surrounding medium is 1.33, and the solid line represents the case where the refractive index nd of the surrounding medium is 1.34. [Figure 12]FIG. 12 is a diagram showing the relationship between the wavelength of incident light and reflectance when the refractive index nd of the glass constituting the optical prism in a detection device according to one embodiment of the present invention is set to 2.5. In the diagram, the dashed line represents the case where the refractive index nd of the surrounding medium is 1.33, and the solid line represents the case where the refractive index nd of the surrounding medium is 1.34. [Figure 13] FIG. 13 is a diagram showing the relationship between the wavelength of incident light and reflectance when the refractive index nd of the glass constituting the optical prism in a detection device according to one embodiment of the present invention is set to 3.0. In the diagram, the dashed line represents the case where the refractive index nd of the surrounding medium is 1.33, and the solid line represents the case where the refractive index nd of the surrounding medium is 1.34. [Figure 14] FIG. 14 is a diagram showing the relationship between the apex angle α and the refractive index sensitivity when the refractive index nd of the glass constituting the optical prism is set to 1.9 in a detection device according to one embodiment of the present invention. [Figure 15] FIG. 15 is a diagram showing the relationship between the apex angle α and the refractive index sensitivity when the refractive index nd of the glass constituting the optical prism is set to 2.5 in a detection device according to one embodiment of the present invention. [Figure 16] FIG. 16 is a diagram showing the relationship between the apex angle α and the refractive index sensitivity when the refractive index nd of the glass constituting the optical prism is set to 3.0 in a detection device according to one embodiment of the present invention. [Figure 17] FIG. 17 is a schematic diagram for explaining the optical path when the refractive index nd of the glass constituting the optical prism is set to 1.5 in the detection device of the comparative example. [Figure 18] FIG. 18 is a diagram showing the relationship between the inner incident angle θ2 and reflectance when the wavelength of light emitted from the light source is 633 nm and the refractive index nd of the glass constituting the optical prism is 1.5 in a detection device of the comparative example. [Figure 19] Figure 19 shows the relationship between the outer incident angle θ1 and the inner incident angle θ2 in a detection device of the comparative example when the refractive index nd of the glass constituting the optical prism is 1.5 and the apex angle α of the optical prism is 90°. [Figure 20]Figure 20 shows the relationship between the outer incident angle θ1 and the inner incident angle θ2 in a detection device of the comparative example when the refractive index nd of the glass constituting the optical prism is 1.5 and the apex angle α of the optical prism is 120°. [Figure 21] Figure 21 shows the relationship between the outer incident angle θ1 and the inner incident angle θ2 in a detection device of the comparative example when the refractive index nd of the glass constituting the optical prism is 1.5 and the apex angle α of the optical prism is 140°. [Figure 22] FIG. 22 is a diagram illustrating an example of the configuration of the refractive index sensor according to the first embodiment. [Figure 23] FIG. 23 is a diagram showing the relationship between the exposure time to an octadecanethiol solution and the resonance wavelength in Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0016] Preferred embodiments of the present invention will be described below. However, the following embodiments are merely examples, and the present invention is not limited to the following embodiments. In addition, in each drawing, components having substantially the same functions may be referred to by the same reference numerals.

[0017] [Detection device] Fig. 1 is a schematic diagram showing the configuration of a detection device according to one embodiment of the present invention, and Fig. 2 is a schematic cross-sectional view showing a sensor unit constituting the detection device according to one embodiment of the present invention.

[0018] 1, the detection device 1 includes a light source 2, a sensor unit 3, and a detector 4. The sensor unit 3 also includes an optical prism 5 and a metal thin film 6.

[0019] 2, the optical prism 5 has a light incident surface 5a, a bottom surface 5b, and a light exit surface 5c. In this embodiment, the optical prism 5 has a triangular prism shape, and the cross-sectional shape of the optical prism 5 is triangular. However, the shape of the optical prism 5 is not particularly limited, and the cross-sectional shape of the optical prism 5 may be a trapezoid, for example. The metal thin film 6 is provided on the bottom surface 5b of the optical prism 5.

[0020] Returning to FIG. 1 , in the detection device 1, light emitted from the light source 2 is collected by the optical lens 7 and enters the polarizing filter 8. The polarizing filter 8 separates the light into an s-polarized component and a p-polarized component, of which the p-polarized component (hereinafter sometimes simply referred to as light) is emitted toward the optical prism 5. The light that reaches the optical prism 5 is refracted at the light incident surface 5a and travels toward the bottom surface 5b. The light that reaches the bottom surface 5b is reflected by the metal thin film 6 and travels toward the light exit surface 5c. The light that reaches the light exit surface 5c is refracted at the light exit surface 5c, collected by the optical lens 9, and travels toward the detector 4. In this manner, in the detection device 1, light reaches the detector 4 and is detected.

[0021] The detection device 1 of this embodiment is configured so that light reaching the bottom surface 5b of the optical prism 5 is totally reflected by the metal thin film 6. In this detection device 1, surface plasmon resonance (propagating surface plasmon resonance) occurs at a specific incident resonance angle. At this time, the incident resonance angle changes due to changes in the refractive index of the detection target 10 and the adsorption and desorption of substances to and from the surface 6a of the metal thin film 6. By measuring or sensing these changes, it is possible to detect the refractive index nd of the detection target 10 and the substances contained therein, and to track changes in their state. Therefore, the detection device 1 can be used by placing the detection target 10 on the surface 6a of the metal thin film 6, and can be used in fields such as refractive index sensors, biosensors, and chemical sensors.

[0022] In the detection device 1 of this embodiment, the optical prism 5 is made of glass having a refractive index nd of 1.9 or more and 3.0 or less. Furthermore, in the detection device 1, the angle α between the light incident surface 5a and the light exit surface 5c of the optical prism 5 is 140° or more and less than 180°. As shown in FIG. 2 , in this embodiment, the cross-sectional shape of the optical prism 5 is triangular, and therefore the angle α between the light incident surface 5a and the light exit surface 5c corresponds to the apex angle of the triangle. However, if the cross-sectional shape of the optical prism 5 is trapezoidal, the angle α between the light incident surface 5a and the light exit surface 5c may be the angle between an imaginary line extending in the direction of the light incident surface 5a and an imaginary line extending in the direction of the light exit surface 5c. Furthermore, in the detection device 1, the optical axis X connecting the light source 2 and the detector 4 and the bottom surface 5b of the optical prism 5 are substantially parallel. In this embodiment, "substantially parallel" is used to mean not only perfect parallelism but also a case where there is an error of ±3.0°. However, it is desirable to design the optical axis X connecting the light source 2 and the detector 4 and the bottom surface 5b of the optical prism 5 to be perfect parallel.

[0023] The detection device 1 of this embodiment has the above overall configuration, and therefore can simplify the entire device while increasing the degree of freedom in optical design.

[0024] More specifically, in the detection device 1 of this embodiment, sensing using surface plasmon resonance can be performed simply by installing the sensor unit 3 between the light source 2 and the detector 4. Therefore, the detection device 1 does not require a mechanical mechanism for precisely controlling the angle of incidence or the angle of reflection using, for example, a rotating stage, and the entire device can be simplified and made smaller.

[0025] Furthermore, in the detection device 1 of this embodiment, the optical prism 5 is made of glass with a refractive index nd of 1.9 or more and 3.0 or less, so the height of the optical axis X connecting the light source 2 and the detector 4 relative to the bottom surface 5b can be made higher.

[0026] Fig. 3 is a schematic diagram illustrating the optical path when the refractive index nd of the glass constituting the optical prism is set to 2.0 in a detection device according to one embodiment of the present invention, and Fig. 17 is a schematic diagram illustrating the optical path when the refractive index nd of the glass constituting the optical prism is set to 1.5 in a detection device of a comparative example.

[0027] 3 and 17, when the refractive index nd of the optical prism 5 is 2.0, the height h of the optical axis X relative to the bottom surface 5b can be made higher than when the refractive index nd of the optical prism 105 is 1.5. As will be described later, when the refractive index nd of the optical prism 5 is 2.0, the inner incident angle θ2 that causes resonance is smaller than when the refractive index nd of the optical prism 105 is 1.5. Therefore, from this point of view, it is clear that when the refractive index nd of the optical prism 5 is 2.0, the height h of the optical axis X relative to the bottom surface 5b can be made higher than when the refractive index nd of the optical prism 105 is 1.5.

[0028] In this way, in the detection device 1 of this embodiment, by constructing the optical prism 5 from glass with a refractive index nd of 1.9 or more, the height h of the optical axis X relative to the bottom surface 5b can be made larger, and therefore, compared to the case where the optical axis X is positioned very close to the bottom surface as shown in FIG. 17, the degree of freedom in the optical design of the detection device 1 can be increased, for example, by increasing the beam diameter of the light emitted from the light source 2.

[0029] In this embodiment, the ratio (h / H) of the height h of the optical axis X from the bottom surface 5b to the height H of the optical prism 5 from the bottom surface 5b is preferably 0.4 or more, more preferably 0.5 or more, even more preferably 0.6 or more, and is preferably 0.95 or less. When the ratio (h / H) is within the above range, the degree of freedom in the optical design of the detection device 1 can be further increased.

[0030] Furthermore, in the detection device 1 of this embodiment, the angle α between the light incident surface 5a and the light exit surface 5c of the optical prism 5 is 140° or more and less than 180°, thereby increasing the refractive index sensitivity of the detection device 1. As will be described later, the larger the refractive index nd of the glass constituting the optical prism 5, the larger the angle α between the light incident surface 5a and the light exit surface 5c of the optical prism 5 can be.

[0031] The angle α between the light incident surface 5a and the light exit surface 5c of the optical prism 5 is preferably 140° or more and less than 180° when the refractive index nd of the glass constituting the optical prism 5 is 1.9 to 3.0, preferably 140° or more and 160° or less when the refractive index nd of the glass constituting the optical prism 5 is 2.0 to 2.7, and preferably 140° or more and 150° or less when the refractive index nd of the glass constituting the optical prism 5 is 2.0 to 2.5. In this case, the refractive index sensitivity of the detection device 1 can be further improved.

[0032] In this embodiment, the light emitted from the light source 2 may be, for example, visible light or near-infrared light. In particular, the wavelength of the light emitted from the light source 2 is preferably 600 nm or more and 1500 nm or less. For example, if the metal thin film 6 is made of Au, the wavelength of the light emitted from the light source 2 is more preferably 600 nm or more and 1200 nm or less. For example, if the metal thin film 6 is made of Ag, the wavelength of the light emitted from the light source 2 is more preferably 400 nm or more and 1800 nm or less. The light emitted from the light source 2 may be incoherent light. As described above, the detection device 1 of this embodiment can increase the height h of the optical axis X relative to the bottom surface 5b, thereby increasing the degree of freedom in optical design. Therefore, the detection device 1 can be suitably used in detection devices that use incoherent light.

[0033] Furthermore, the beam diameter of the light emitted from the light source 2 is not particularly limited, but can be, for example, 0.01 mm or more, preferably 1 mm or more, and preferably 10 mm or less. As described above, in the detection device 1 of this embodiment, the height h of the optical axis X relative to the bottom surface 5b can be made larger, which increases the degree of freedom in optical design, and therefore the device can be suitably used even when the beam diameter of the light emitted from the light source 2 is increased.

[0034] In this embodiment, the refractive index nd of the glass constituting the optical prism 5 is 1.9 or more and 3.0 or less. The refractive index nd of the glass constituting the optical prism 5 is preferably 2.0 or more, preferably 2.7 or less, and more preferably 2.5 or less. When the refractive index nd of the glass constituting the optical prism 5 is equal to or greater than the above-mentioned lower limit, the height h of the optical axis X relative to the bottom surface 5b can be increased, thereby increasing the degree of freedom in the optical design of the detection device 1. Furthermore, when the refractive index nd of the glass constituting the optical prism 5 is equal to or greater than the above-mentioned lower limit, the dip wavelength (described later) shifts to the longer wavelength side, thereby reducing the loss due to the metal thin film 6 and increasing the refractive index sensitivity of the detection device 1. Furthermore, when the refractive index nd of the glass constituting the optical prism 5 is within the above-mentioned range, the degree of freedom in the optical design of the detection device 1 can be increased while also increasing the refractive index sensitivity of the detection device 1.

[0035] The refractive index nd can be measured using the well-known V-block method. For example, a sample is cut to 30 mm x 30 mm x 5 mm, one end is polished at a right angle, and the polished surface is then polished to a mirror finish. The refractive index of the mirror-polished sample is measured using a precision refraction system KPR-2000 (Shimadzu Corporation) at the d line of a He lamp.

[0036] In this embodiment, the refractive index nC of the glass constituting the optical prism 5 is preferably 1.88 or more and 2.99 or less. The refractive index nC of the glass constituting the optical prism 5 is preferably 1.89 or more, and preferably 2.69 or less, more preferably 2.49 or less.

[0037] The glass constituting the optical prism 5 is not particularly limited as long as it has a refractive index nd of 1.9 or more and 3.0 or less and is transparent to light with a wavelength of 600 nm or more and 1500 nm or less. For example, glass containing at least one selected from TiO2, Ta2O5, Nb2O5, and La2O3 is preferred. For example, the glass constituting the optical prism 5 preferably contains, in mass %, 10% to 90% of TiO2 + Ta2O5 + Nb2O5 + La2O3.

[0038] The following describes the reasons for the preferred range of the glass composition of the glass that constitutes the optical prism 5. In the explanation of the range of each component, % refers to % by mass unless otherwise specified.

[0039] TiO2, Ta2O5, Nb2O5, and La2O3 are components that significantly increase the refractive index nd of the glass. The content of TiO2 + Ta2O5 + Nb2O5 + La2O3 (total amount of TiO2, Ta2O5, Nb2O5, and La2O3) is preferably 10% to 90%. Specifically, the lower limit of the content of TiO2 + Ta2O5 + Nb2O5 + La2O3 is preferably 10% or more, 20% or more, 30% or more, 40% or more, 50% or more, and particularly 60% or more, and the upper limit of the content of TiO2 + Ta2O5 + Nb2O5 + La2O3 is preferably 90% or less, and particularly 80% or less. The preferred contents of each of the components TiO2, Ta2O5, Nb2O5, and La2O3 are as follows:

[0040] The TiO2 content is preferably 0% to 60%. The lower limit of the TiO2 content is preferably 0% or more, 1% or more, 2% or more, 5% or more, and particularly preferably 10% or more, and the upper limit of the TiO2 content is preferably 60% or less, 50% or less, 40% or less, and particularly preferably 30% or less. If the TiO2 content is too high, the glass may be colored and devitrification resistance may be reduced.

[0041] The Ta2O5 content is preferably 0% to 60%. The lower limit of the Ta2O5 content is preferably 0% or more, 1% or more, 2% or more, 5% or more, and particularly preferably 10% or more, and the upper limit of the Ta2O5 content is preferably 60% or less, 50% or less, 40% or less, and particularly preferably 30% or less. If the Ta2O5 content is too high, devitrification resistance is likely to decrease.

[0042] The Nb2O5 content is preferably 0% to 60%. The lower limit of the Nb2O5 content is preferably 0% or more, 1% or more, 2% or more, 5% or more, and particularly preferably 10% or more, and the upper limit of the Nb2O5 content is preferably 60% or less, 50% or less, 40% or less, and particularly preferably 30% or less. If the Nb2O5 content is too high, the liquidus temperature will rise sharply, the liquidus viscosity will decrease, and mass productivity will tend to deteriorate. In addition, the internal transmittance will tend to decrease.

[0043] The La2O3 content is preferably 0% to 60%. The lower limit of the La2O3 content is preferably 0% or more, 1% or more, 2% or more, 5% or more, and particularly preferably 10% or more, and the upper limit of the La2O3 content is preferably 60% or less, 50% or less, 40% or less, and particularly preferably 30% or less. If the La2O3 content is too high, the liquidus viscosity decreases, which tends to deteriorate mass productivity.

[0044] Examples of materials that can be used for the metal thin film 6 include Ag, Au, and Cu. The thickness of the metal thin film 6 is preferably 30 nm or more, more preferably 45 nm or more, and is preferably 70 nm or less, more preferably 55 nm or less. When the thickness of the metal thin film 6 is within the above range, surface plasmons can be excited more easily.

[0045] As the detector 4, for example, a CCD camera, a photodiode, a photomultiplier tube, or a combination of a spectrometer, a CCD camera, a photodiode array, or the like can be used.

[0046] For example, a plastic polarizing film can be used as the polarizing filter 8. Note that the detecting device 1 does not necessarily need to be provided with the polarizing filter 8.

[0047] For example, objective lenses can be used as the optical lenses 7 and 9. Note that the detection device 1 does not necessarily need to include the optical lenses 7 and 9, or may include only one of the optical lenses 7 and 9.

[0048] The refractive index sensitivity of the detector 1 of this embodiment is preferably 1000 nm / RIU or more, more preferably 2000 nm / RIU or more, and preferably 30,000 nm / RIU or less, more preferably 20,000 nm / RIU or less. The refractive index sensitivity (Sn) of the detector 1 can be calculated by dividing the change in dip wavelength (Δλ) by the change in refractive index nd (Δnd) when the dip wavelength changes in accordance with a change in the refractive index nd of the object 10 to be detected (Sn=Δλ / Δnd). When the refractive index sensitivity of the detector 1 is within the above range, it can be suitably used in applications such as a refractive index sensor, biosensor, and chemical sensor.

[0049] The detection device 1 of this embodiment will be described in further detail below using a specific example. As shown in FIG. 2 , the angle between the direction of light incident on the light incident surface 5a of the optical prism 5 and the direction perpendicular to the bottom surface 5b is referred to as the outer incident angle θ1, and the angle between the direction of light incident on the metal thin film 6 and the direction perpendicular to the bottom surface 5b is referred to as the inner incident angle θ2. In the detection device 1 of this embodiment, it is desirable to arrange the optical axis X connecting the light source 2 and the detector 4 parallel to the bottom surface 5b of the optical prism 5, so the outer incident angle θ1 is designed to be 90°. Hereinafter, the angle α between the light incident surface 5a and the light exit surface 5c of the optical prism 5 will be referred to as the apex angle α. A 47-nm-thick Au film was used as the metal thin film 6. An aqueous solution with a refractive index nd = 1.33 was used as the detection target 10.

[0050] Figure 4 shows the relationship between the inner incident angle θ2 and reflectance when the wavelength of light emitted from the light source is 633 nm and the refractive index nd of the glass constituting the optical prism is 2.0 in a detection device according to one embodiment of the present invention. Note that HeNe laser light was used as the light with a wavelength of 633 nm. Figure 4 shows that surface plasmon resonance occurs when the inner incident angle θ2 is approximately 46°.

[0051] Figures 5 to 7 are diagrams showing the relationship between the outer incident angle θ1 and the inner incident angle θ2 when the refractive index nd of the glass constituting the optical prism is 2.0 in a detection device according to one embodiment of the present invention. Note that Figure 5 shows the results when the apex angle α is 90°, Figure 6 shows the results when the apex angle α is 120°, and Figure 7 shows the results when the apex angle α is 140°.

[0052] 5 and 6, when the apex angle α is 90° and 120°, the outer incident angle θ1 is less than 90° at the inner incident angle θ2=46° at which surface plasmon resonance occurs. On the other hand, as shown in Fig. 7, when the apex angle α is 140°, the outer incident angle θ1 is 90° at the inner incident angle θ2=46° at which surface plasmon resonance occurs.

[0053] Similarly, the inner incident angle θ2 at which surface plasmon resonance occurs was determined, and the apex angle α at which the outer incident angle θ1 is 90° was determined for cases where the refractive index nd of the glass constituting the optical prism 5 was 1.9, 2.5, and 3.0. The results confirmed that when nd = 1.9, the outer incident angle θ1 is 90° when the apex angle α is 140°; when nd = 2.5, the outer incident angle θ1 is 90° when the apex angle α is 150°; and when nd = 3.0, the outer incident angle θ1 is 90° when the apex angle α is 160°. From the above, it was confirmed that when the wavelength of light emitted from the light source is 633 nm, the outer incident angle θ1 can be designed to be 90° when the apex angle α is 140° or greater, and when the refractive index nd of the glass constituting the optical prism 5 is in the range of 1.9 to 3.0.

[0054] On the other hand, Fig. 18 shows the relationship between the inner incident angle θ2 and reflectance in a comparative detection device when the wavelength of light emitted from the light source is 633 nm and the refractive index nd of the glass constituting the optical prism is 1.5. Fig. 18 shows that surface plasmon resonance occurs when the inner incident angle θ2 is approximately 73°.

[0055] 19 to 21 are diagrams showing the relationship between the outer incident angle θ1 and the inner incident angle θ2 when the refractive index nd of the glass constituting the optical prism is 1.5 in a detection device of the comparative example. The detection device of the comparative example uses the optical prism 105 shown in FIG. 17. FIG. 19 shows the results when the apex angle α is 90°, FIG. 20 shows the results when the apex angle α is 120°, and FIG. 21 shows the results when the apex angle α is 140°.

[0056] 20 and 21, when the apex angle α is 120° and 140°, the outer incident angle θ1 does not exist at the inner incident angle θ2=73° at which surface plasmon resonance occurs. On the other hand, as shown in FIG. 19, when the apex angle α is 90°, the outer incident angle θ1 is 90° at the inner incident angle θ2=73° at which surface plasmon resonance occurs. Therefore, when the wavelength of light emitted from light source 2 is 633 nm, and the refractive index nd of the glass constituting optical prism 105 is 1.5, the outer incident angle θ1 can be designed to be 90° when the apex angle α is 90°. However, when the apex angle α is 120° or more, it is difficult to design the outer incident angle θ1 to be 90°.

[0057] Figure 8 shows the relationship between the apex angle α of the optical prism and the ratio of the height h of the optical axis from the bottom surface to the height H of the optical prism, with the white circles in the figure indicating the optimal apex angle for the sensor at each refractive index nd. Figure 8 shows results when the refractive index nd of the optical prism 5 is nd = 2.0, 2.5, and 3.0. It also shows results when the refractive index nd of the optical prism 105 is nd = 1.5. The points indicated by white circles on each graph indicate the apex angle α where the outer incident angle θ1 = 90°.

[0058] FIG. 8 shows that the ratio (h / H) of the height h of the optical axis X from the bottom surface 5b to the height H of the optical prism 5 from the bottom surface 5b increases as the refractive index nd of the optical prism 5 increases. In particular, when comparing the apex angle α at which the outer incident angle θ1 is 90°, the ratio (h / H) can be significantly increased by setting the refractive index nd to 1.9 or more and 3.0 or less, compared to when the refractive index nd is 1.5. Specifically, when the refractive index nd is 2.0 and the height H of the optical prism 5 from the bottom surface 5b is 10 mm, the height h of the optical axis X from the bottom surface 5b is 7.28 mm. On the other hand, when the refractive index nd is 1.5 and the height H of the optical prism 105 from the bottom surface 5b is 10 mm, the height h of the optical axis X from the bottom surface 5b is 2.37 mm, significantly limiting the beam diameter of the incident light. This makes it difficult to use coherent light for the light source 2.

[0059] Next, a specific example of refractive index sensitivity measurement by the detection device 1 will be described.

[0060] 9 is a graph showing the relationship between the wavelength of incident light and reflectance when the refractive index nd of the glass constituting the optical prism in a detection device according to one embodiment of the present invention is set to 2.0. In the graph, the dashed line represents the case where the refractive index nd of the surrounding medium is 1.33, and the solid line represents the case where the refractive index nd of the surrounding medium is 1.34. Note that FIG. 9 shows results when the apex angle α is 140° and the outer incident angle θ1 is 90°. FIG. 9 also shows results when an aqueous solution with a refractive index nd = 1.34 is used as the detection target 10 in addition to an aqueous solution with a refractive index nd = 1.33.

[0061] From FIG. 9, it can be seen that when the refractive index nd of the aqueous solution serving as the detection object 10 is 1.34, the dip wavelength at which surface plasmon resonance occurs is larger than when the refractive index nd of the aqueous solution is 1.33.

[0062] FIG. 10 shows the relationship between the apex angle α and the refractive index sensitivity when the refractive index nd of the glass constituting the optical prism is 2.0 in a detection device according to one embodiment of the present invention. The refractive index sensitivity is the amount of change in the resonant wavelength that occurs when the refractive index nd of the surrounding medium changes by 1; the higher the sensitivity, the better. The resonant wavelength is the wavelength at which the reflectance is smallest when white light is used as the light source, and at this wavelength, surface plasmon resonance is strong. Furthermore, as shown in FIG. 9, the refractive index sensitivity (Sn) was calculated by dividing the change in the refractive index nd of the aqueous solution (Δnd) by the change in the dip wavelength (Δλ) when the refractive index nd of the aqueous solution changes (Sn = Δλ / Δnd). From FIG. 10, it can be seen that when the apex angle α of the optical prism 5 is 140° or greater, the refractive index sensitivity increases as the apex angle α increases.

[0063] 11 to 13 are diagrams showing the relationship between the wavelength of incident light and reflectance in a detection device according to one embodiment of the present invention. In the diagrams, the dashed line represents the case where the refractive index nd of the surrounding medium is 1.33, and the solid line represents the case where the refractive index nd of the surrounding medium is 1.34. Note that FIG. 11 shows the results when the refractive index nd of the glass constituting the optical prism 5 is 1.9 and the apex angle α is 140°, FIG. 12 shows the results when the refractive index nd of the glass constituting the optical prism 5 is 2.5 and the apex angle α is 150°, and FIG. 13 shows the results when the refractive index nd of the glass constituting the optical prism 5 is 3.0 and the apex angle α is 160°. The other conditions are the same as those in FIG. 9.

[0064] 11 to 13, as in FIG. 9, it can be seen that when the refractive index nd of the aqueous solution, which is the detection target 10, is 1.34, the dip wavelength at which surface plasmon resonance occurs is larger than when the refractive index nd of the aqueous solution is 1.33.

[0065] Figures 14 to 16 are diagrams showing the relationship between the apex angle α and the refractive index sensitivity in a detection device according to one embodiment of the present invention. Fig. 14 shows the results when the refractive index nd of the glass constituting the optical prism 5 is set to 1.9, Fig. 15 shows the results when the refractive index nd of the glass constituting the optical prism 5 is set to 2.5, and Fig. 16 shows the results when the refractive index nd of the glass constituting the optical prism 5 is set to 3.0.

[0066] From Figure 14, it can be seen that when the refractive index nd of the glass constituting the optical prism 5 is 1.9, the refractive index sensitivity increases as the apex angle α increases when the apex angle α is 140° or greater. From Figure 15, it can be seen that when the refractive index nd of the glass constituting the optical prism 5 is 2.5, the refractive index sensitivity increases as the apex angle α increases when the apex angle α is 150° or greater. Furthermore, from Figure 16, it can be seen that when the refractive index nd of the glass constituting the optical prism 5 is 3.0, the refractive index sensitivity increases as the apex angle α increases when the apex angle α is 160° or greater.

[0067] The results are shown in Table 1 below. Note that the apex angle α in Table 1 indicates the apex angle when the resonance wavelength is near 600 nm. The surface plasmon resonance wavelength is shown as the result for the apex angle α in Table 1.

[0068] [Table 1]

[0069] The present invention will be described in more detail below with reference to specific examples. The present invention is not limited to the following examples, and can be practiced with appropriate modifications within the scope of the present invention.

[0070] Example 1 A refractive index sensor was fabricated using a glass prism with a refractive index nd of 2.0, a vertex angle α of 140°, and a height H of 10 mm. The glass prism was composed of glass containing, by mass, at least 10% of TiO2 + Ta2O5 + Nb2O5 + La2O3. The metal thin film on the bottom of the glass prism was made of Au (gold thin film), with a film thickness of 50 nm. A halogen lamp (Ocean Optics) was used as the light source, and white incident light was used. The incident light passed through an objective lens and a polarizing plate (polarizing filter). The light emitted from the glass prism was detected after passing through the objective lens. An optical spectrometer (USB-2000, Ocean Optics) was used as the detector. The fabricated refractive index sensor is shown in Figure 22. A mixed solvent of water and ethanol was used as the detection target. The refractive index nd of water is 1.33, and the refractive index nd of ethanol is 1.36. The refractive index nd of the mixed solvent was controlled by mixing water and ethanol. Five types of samples were prepared, with volumetric water-to-ethanol ratios of 1:0, 3:1, 1:1, 1:3, and 0:1, and the resonance wavelength was measured. Figure 10 shows that the refractive index sensitivity was 1000 nm / RIU, and this value was used to calculate the wavelength change. The results are shown in Table 2. As shown in Table 2, in this example, the experimental and simulated values ​​for the amount of change in resonance wavelength generally matched, confirming that the refractive index sensor functioned well.

[0071] [Table 2]

[0072] Example 2 Next, a chemical sensor for detecting substances was fabricated. The sensor configuration was the same as in Example 1. The detection target was a 0.01 mM octadecanethiol solution in ethanol. When octadecanethiol comes into contact with a thin gold film, a self-assembled monolayer grows on the surface of the gold film. This self-assembled monolayer optically behaves as a dielectric thin film. Figure 23 shows the relationship between elapsed time (exposure time) and resonance wavelength obtained using the fabricated chemical sensor. When the octadecanethiol solution was exposed to the surface of the thin gold film on the bottom of the glass prism, the resonance wavelength began to change. 900 seconds after the start of exposure, the monolayer formation was completed and the change ceased. The observed resonance wavelength change was 4 nm. Simulations showed that a 1 nm thickness of the dielectric film on the thin gold film shifts the resonance wavelength by 2 nm, so the observed 4 nm resonance wavelength change indicates that the thickness of the formed dielectric film was approximately 2 nm. This thickness closely matches the 1.8 nm length of the octadecanethiol molecule measured by ellipsometry (Reference 1).

[0073] [References] Reference 1: CD Bain, EB Troughton, Y.-T. Tao, J. Evall, GM Whitesides, and Ralph G. Nuzzo, “Formation of Monolayer Films by the Spontaneous assembly of Organic Thiols from Solution onto Gold”, J. Am. Chem. Soc. 111 (1989) 321-335 [Explanation of symbols]

[0074] 1...Detection device 2...Light source 3...Sensor section 4...Detector 5...Optical prism 5a...Light incidence surface 5b…Bottom surface 5c...Light exit surface 6...Metal thin film 6a…Surface 7,9...Optical lenses 8...Polarizing filter 10...Detection target

Claims

1. A detection device utilizing surface plasmon resonance, A light source and a sensor unit including an optical prism having a light incident surface, a bottom surface, and a light exit surface, and a metal thin film provided on the bottom surface of the optical prism, the metal thin film reflecting light emitted from the light source and incident on the light incident surface toward the light exit surface; a detector that detects light reflected by the metal thin film of the sensor unit, the optical prism is made of glass having a refractive index nd of 1.9 or more and 3.0 or less, In the optical prism, the angle between the light incident surface and the light exit surface is 140° or more and less than 180°, A detection device, wherein an optical axis connecting the light source and the detector is approximately parallel to the bottom surface of the optical prism.

2. 2. The detection device according to claim 1, wherein the wavelength of the light emitted from the light source is not less than 600 nm and not more than 1500 nm.

3. 3. The detection device according to claim 1, wherein the light emitted from the light source is incoherent light.

4. 3. The detection device according to claim 1, wherein a ratio of a height of the optical axis from the bottom surface of the optical prism to a height of the optical axis from the bottom surface of the optical prism is 0.4 or more.

5. 3. The detection device according to claim 1, wherein the beam diameter of the light emitted from the light source is 1 mm or more.

6. 3. The detection device according to claim 1, wherein the refractive index sensitivity is 1000 nm / RIU or more and 30000 nm / RIU or less.

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