Ion sensor and ion detection system using the same

Abstract

To provide an ion sensor capable of detecting ions included in a liquid sample.SOLUTION: An ion sensor for detecting cations included in a liquid sample includes a photonic crystal having a dropped liquid sample. The photonic crystal includes: a resin having a plurality of holes having a diameter smaller than the wavelength of visible light and periodically arranged; and a plurality of metal oxide nano particles having a single nanometer size and dispersed in the resin. The resin includes an ionophore capable of selectively extracting the cations and dye deprotonated when extracting the cations by the ionophore; the reflection spectrum of the photonic crystal has a peak in the visible range; and a wavelength region including the peak of the reflection spectrum of the photonic crystal overlaps with a wavelength region including the peak of the absorption spectrum of the deprotonated dye.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to an ion sensor and an ion detection system using the same, and more particularly to an ion sensor that detects cations contained in a liquid sample and an ion detection system using the same. [Background technology]

[0002] In recent years, research and development of sensors that apply photonic crystals has been progressing. In these sensors, a liquid sample that may contain target substances such as DNA or antibodies is dropped onto a photonic crystal. Light is then irradiated onto the liquid sample, and the reflected light is detected by a photodetector. By analyzing the reflection spectrum obtained in this way, the target substance in the liquid sample can be detected.

[0003] Furthermore, Japanese Patent Laid-Open Publication No. 2005-146042 (Patent Document 1) discloses that the optical properties of a resin, such as the refractive index, can be adjusted by incorporating composite metal oxide nanoparticles consisting of Si and at least one metal element other than silicon (Si) into the resin (see, for example, paragraph

[0012] of Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-146042 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-241985 [Patent Document 3] International Publication No. 2010 / 064664 [Patent Document 4] International Publication No. 2016 / 035689 [Non-patent literature]

[0005] [Non-Patent Document 1] S. Aki, T. Endo, K. Sueyoshi, H. Hisamoto, Anal. Chem. 2014, 86, 11986-11991 [Non-patent document 2] S. Aki, K. Sueyoshi, H. Hisamoto, T. Endo, Anal. Sci. 2017, 33, 1247-1251. Summary of the Invention [Problem to be solved by the invention]

[0006] The use of resin as a substrate for photonic crystals is being considered. When a sensor using a photonic crystal containing resin detects a target substance in a liquid sample using the aforementioned detection principle, the detection accuracy of the target substance depends on the difference between the refractive index of the resin and the refractive index of the liquid sample. Here, this difference is also referred to as the "refractive index difference." The greater the refractive index difference, the higher the detection accuracy. However, the refractive index difference between common resins (such as vinyl chloride) being considered for use as photonic crystal substrates and the main component of a liquid sample (typically water) is relatively small. Therefore, when the target substance is a minute substance such as an ion or a taste substance, its detection is difficult.

[0007] Increasing the refractive index of a resin increases the difference in refractive index, improving the detection accuracy of the target substance. Therefore, it is conceivable to incorporate "metal oxide nanoparticles," which are nanoparticles made of metal oxides known to have a high refractive index, into the resin. However, even when metal oxide nanoparticles are mixed with a resin, the metal oxide nanoparticles are difficult to disperse in the resin. Therefore, it has been difficult to fabricate a photonic crystal using a resin in which metal oxide nanoparticles are uniformly dispersed as a substrate.

[0008] The present disclosure has been made to solve the above problems, and its object is to provide a photonic crystal element in which metal oxide nanoparticles are uniformly dispersed in a resin. Another object of the present disclosure is to provide an ion sensor capable of detecting ions contained in a liquid sample. Yet another object of the present disclosure is to provide a tasting substance sensor capable of detecting tasting substances contained in a liquid sample. [Means for solving the problem]

[0009] (1) A photonic crystal element according to one aspect of the present disclosure includes a resin containing a copolymer of vinyl chloride, vinyl acetate, and vinyl alcohol, and a plurality of holes periodically arranged, each hole having a diameter smaller than the wavelength of visible light, and a plurality of zirconium oxide nanoparticles dispersed in the resin.

[0010] (2) Preferably, each of the plurality of zirconium oxide nanoparticles has a size of a single nanometer.

[0011] (3) An ion sensor according to another aspect of the present disclosure detects cations contained in a liquid sample. The ion sensor includes a photonic crystal onto which the liquid sample is dropped. The photonic crystal includes a resin in which a plurality of holes, each with a diameter smaller than the wavelength of visible light, are periodically arranged, and a plurality of metal oxide nanoparticles dispersed in the resin. The resin includes an ionophore capable of selectively extracting cations, and a dye that is deprotonated when the cations are extracted by the ionophore. The reflection spectrum of the photonic crystal has a peak in the visible range. The wavelength range including the peak of the reflection spectrum of the photonic crystal overlaps with the wavelength range including the peak of the absorption spectrum of the dye in a deprotonated state.

[0012] (4) Preferably, each of the plurality of metal oxide nanoparticles is a zirconium oxide nanoparticle, and the resin includes a copolymer of vinyl chloride, vinyl acetate, and vinyl alcohol.

[0013] (5) Preferably, the cation is potassium ion, the ionophore is valinomycin, and the dye is KD-M11.

[0014] (6) An ion detection system according to yet another aspect of the present disclosure includes a holding member configured to hold the ion sensor, a light source that emits visible light for irradiating a liquid sample, a photodetector that detects reflected light from the liquid sample, and a detection device that detects cations based on the reflected light detected by the photodetector.

[0015] (7) A taste substance sensor according to yet another aspect of the present disclosure detects a taste substance contained in a liquid sample. The taste substance sensor includes a photonic crystal onto which the liquid sample is dropped. The photonic crystal includes a resin in which a plurality of holes, each having a diameter smaller than the wavelength of visible light, are periodically arranged, and a plurality of metal oxide nanoparticles dispersed in the resin. The resin includes lipids that selectively adsorb the taste substance. The reflection spectrum of the photonic crystal has a peak in the visible range.

[0016] (8) The taste substance is sucrose. The lipids are palmitic acid and TDAB (1,3,5-Tris(diphenylamino)benzene).

[0017] (9) The taste substance is sodium saccharin. The lipid is TDAB. (10) A taste substance detection system according to yet another aspect of the present disclosure includes a holding member configured to hold the taste substance sensor, a light source that emits visible light for irradiating a liquid sample, a photodetector that detects reflected light from the liquid sample, and a detection device that detects the taste substance based on the reflected light detected by the photodetector.

[0018] (11) A method for manufacturing a photonic crystal element according to yet another aspect of the present disclosure includes first to fifth steps. The first step is preparing a template made of a gas-permeable material and including a periodic arrangement of multiple pillars, each with a diameter smaller than the wavelength of visible light. The second step is preparing a liquid resin containing a copolymer of vinyl chloride, vinyl acetate, and vinyl alcohol, and multiple zirconium oxide nanoparticles. The third step is dropping the liquid resin onto a substrate. The fourth step is transferring the template to the liquid resin and evaporating the solvent of the liquid resin through the template to form a solidified resin. The fifth step is removing the template from the resin.

[0019] (12) Preferably, the step of preparing a mold (first step) includes a step of forming the mold from PDMS (polydimethyl siloxane). [Effects of the Invention]

[0020] According to the present disclosure, a photonic crystal element in which metal oxide nanoparticles are uniformly dispersed in a resin can be provided. Also, according to the present disclosure, an ion sensor capable of detecting ions contained in a liquid sample can be provided. Furthermore, according to the present disclosure, a taste substance sensor capable of detecting taste substances contained in a liquid sample can be provided. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a diagram schematically showing the overall configuration of an ion detection system according to an embodiment of the present invention. [Figure 2] FIG. 2 is an exploded perspective view showing the configuration of the ion sensor and the holding member in more detail. [Figure 3] FIG. 2 is an enlarged perspective view schematically showing an ion sensor. [Figure 4] FIG. 4 is a cross-sectional view of the ion sensor taken along line IV-IV shown in FIG. [Figure 5] FIG. 1 shows a scanning electron microscope image of a mold. [Figure 6] FIG. 10 shows an atomic force microscope image of a mold. [Figure 7] 10A and 10B are diagrams illustrating the cross-sectional shape of a pillar array formed on a mold. [Figure 8] FIG. 1 shows a scanning electron microscope image of a photonic crystal. [Figure 9] FIG. 1 shows an atomic force microscope image of a photonic crystal. [Figure 10] 1A and 1B are diagrams illustrating the cross-sectional shape of a hole array formed in a photonic crystal. [Figure 11] 1 is a conceptual diagram for explaining the principle of detecting a target substance based on a change in the reflection spectrum of a photonic crystal. FIG. [Figure 12] FIG. 1 is a conceptual diagram for explaining the principle of ion detection based on changes in the absorption spectrum of a dye. [Figure 13] FIG. 1 is a diagram illustrating a combination of a resin and metal oxide nanoparticles. [Figure 14] FIG. 14 is a diagram showing the state of each mixed liquid shown in FIG. 13. [Figure 15] FIG. 2 is a diagram showing the structural formula of a dye (NCODE) in a comparative example. [Figure 16] FIG. 2 is a diagram showing the structural formula of a dye (KD-M11) in the present embodiment. [Figure 17] FIG. 1 is a diagram showing the structural formula of an ionophore (valinomycin) in the present embodiment. [Figure 18] FIG. 10 is a diagram showing the reflection spectrum of a photonic crystal fabricated using the fifth mixed liquid. [Figure 19] FIG. 1 shows the absorption spectrum of NCODE. [Figure 20] FIG. 1 shows the absorption spectrum of KD-M11. [Figure 21] FIG. 2 is a diagram for explaining the compositions of photonic crystals in Comparative Examples 1 and 2 and the present embodiment. [Figure 22] FIG. 10 is a diagram summarizing the measurement results of the reflection spectrum of the ion sensor according to Comparative Example 1. [Figure 23]FIG. 10 is a diagram summarizing the measurement results of the reflection spectrum of the ion sensor according to Comparative Example 2. [Figure 24] FIG. 10 is a diagram summarizing measurement results of the reflection spectrum of the ion sensor according to the present embodiment. [Figure 25] 1 is a flowchart illustrating a method for manufacturing an ion sensor according to the present embodiment. [Figure 26] 3A to 3C are schematic process diagrams illustrating a method for manufacturing an ion sensor according to the present embodiment. [Figure 27] FIG. 1 shows the composition of a tastant sensor for detecting sucrose. [Figure 28] FIG. 1 shows the composition of a tastant sensor for detecting saccharin sodium. [Figure 29] FIG. 10 is a diagram showing the structural formulas of a taste substance, a lipid used for detecting the taste substance, and a plasticizer for a resin in this modified example. [Figure 30] FIG. 10 is a diagram showing the results of measuring the reflectance spectrum when sucrose solutions of different concentrations are dropped. [Figure 31] FIG. 31 shows the relationship between reflection intensity and sucrose concentration shown in FIG. 30. [Figure 32] FIG. 10 is a diagram showing the results of measuring the reflectance spectrum when saccharin sodium solutions of different concentrations are dropped. [Figure 33] FIG. 33 shows the relationship between the reflection intensity and saccharin sodium concentration shown in FIG. 32. [Figure 34] FIG. 10 is a diagram showing the results of creating a calibration curve for sucrose in this modified example. [Figure 35] FIG. 10 is a diagram showing the results of creating a calibration curve for sucrose in a comparative example. [Figure 36] FIG. 10 is a diagram showing the results of creating a calibration curve for saccharin sodium in this modified example. [Figure 37] FIG. 1 is a diagram showing the results of creating a calibration curve for saccharin sodium in a comparative example. [Figure 38] FIG. 10 is a diagram showing the measurement results when a saccharin sodium solution is dropped onto a sucrose taste substance sensor. [Figure 39] FIG. 10 is a diagram showing the measurement results when an aspartame solution is dropped onto a taste substance sensor for sucrose. [Figure 40] FIG. 10 is a diagram showing the measurement results when a sucrose solution is dropped onto a taste substance sensor for saccharin sodium. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0023] In the present disclosure and its embodiments, "nanometer order" means a range of 1 nm to 1,000 nm (=1 μm), and "single nanometer" means a range of 1 nm to 10 nm.

[0024] In the present disclosure and its embodiments, "metal oxide nanoparticles" refer to metal oxide particles having a size on the order of nanometers. The shape of the metal oxide particles includes, but is not limited to, a spherical shape, and may be an ellipsoidal shape, a rod shape, or the like. When the metal oxide particles are ellipsoidal, at least one of the lengths of the minor axis and the major axis of the ellipsoid may be on the order of nanometers. When the metal oxide particles are rod-shaped, at least one of the width and length of the rod may be on the order of nanometers.

[0025] In the present disclosure and its embodiments, "visible light" or light in the "visible range" refers to light having a wavelength range spanning at least a portion of 360 nm to 830 nm, and preferably light having a wavelength range spanning at least a portion of 400 nm to 700 nm. "White light" refers to light having a wavelength range spanning the entire visible range.

[0026] In the present disclosure and its embodiments, "the wavelength ranges including the peaks of two spectra overlap" means that at least a portion of the full width at half maximum of the first spectrum and at least a portion of the full width at half maximum of the second spectrum are common.

[0027] In the present disclosure and its embodiments, the term "hole" refers to a micropore with a diameter on the order of nanometers. The depth of the hole may be on the order of nanometers or may be deeper. The shape of the hole may be a cylinder or a truncated cone (tapered or inverted tapered). Furthermore, each hole may be a through hole or a blind hole.

[0028] [Embodiment Mode] <System configuration> FIG. 1 is a diagram showing a schematic diagram of the overall configuration of an ion detection system according to this embodiment. In the following description, the X and Y directions represent horizontal directions. The X and Y directions are perpendicular to each other. The Z direction represents the vertical direction. The direction of gravity is downward in the Z direction. Furthermore, upward in the Z direction may be abbreviated as "upward," and downward in the Z direction may be abbreviated as "downward."

[0029] 1, the ion detection system 100 includes a light source 2, a holding member 3, a photodetector 4, and a control device 5. An ion sensor 1 is placed on the holding member 3. A liquid sample SPL that may contain cations, which are substances to be detected, is dropped onto the ion sensor 1. The detailed configuration of the ion sensor 1 will be described later.

[0030] The light source 2 emits visible light to irradiate the liquid sample SPL on the ion sensor 1 in response to a command from the control device 5. The light irradiated from the light source 2 is also referred to as "irradiation light L1." In this embodiment, white light is emitted from the light source 2. As one example, a tungsten halogen lamp can be used as the light source 2. However, the type of light source 2 is not limited to this, and may be, for example, a xenon lamp or a white laser.

[0031] The light source 2 is fixed to a Z-axis stage (not shown). By adjusting this Z-axis stage, the distance between the light source 2 and the holding member 3 can be set appropriately.

[0032] The holding member 3 is configured to be able to hold the ion sensor 1. The detailed configuration of the holding member 3 will be described with reference to FIG.

[0033] When the liquid sample SPL is irradiated with the illumination light L1, a portion of the illumination light L1 is absorbed by the liquid sample SPL, and a portion of the light that is not absorbed is reflected by the ion sensor 1. The light from the ion sensor 1 is also referred to as "reflected light L2." The reflected light L2 is detected by the photodetector 4.

[0034] The photodetector 4 is a detector in which photoelectric conversion elements capable of detecting light in the wavelength range (visible range) of the reflected light L2 are arranged in an array. Specifically, the photodetector 4 includes a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal-Oxide-Semiconductor) image sensor. In response to a command from the control device 5, the photodetector 4 detects the reflected light L2 from the ion sensor 1 and outputs the detection result to the control device 5.

[0035] The control device 5 is a microcomputer including a processor 51 such as a CPU (Central Processing Unit), a memory 52 such as a ROM (Read Only Memory) and a RAM (Random Access Memory), and an input / output port (not shown). The control device 5 controls each device in the ion detection system 100 (the light source 2, the XY-axis stage 31 (see FIG. 2), the Z-axis stage, and the photodetector 4). The control device 5 also creates a reflection spectrum of the liquid sample SPL based on the detection results from the photodetector 4, and detects cations from the reflection spectrum. In other words, the control device 5 corresponds to the "detection device" according to the present disclosure.

[0036] 1 is merely an example for explaining the ion detection principle in this embodiment. The optical system of the ion detection system 100 is not limited to the configuration shown in Fig. 1 as long as it is possible to irradiate the ion sensor 1 with irradiation light L1 from the light source 2 and to capture reflected light L2 from the ion sensor 1 in the photodetector 4. For example, the optical system of the ion detection system 100 may be configured to further include optical components (not shown) such as mirrors, dichroic mirrors, lenses, prisms, and optical fibers.

[0037] 2 is an exploded perspective view showing in more detail the configurations of the ion sensor 1 and the holding member 3. Referring to Fig. 2, the ion sensor 1 includes a substrate 11 and a photonic crystal 12. The holding member 3 includes an XY axis stage 31, a silicon sheet 32, and a resin frame 33.

[0038] The substrate 11 is provided to ensure the mechanical strength of the ion sensor 1 and is, for example, a glass substrate (glass slide). Alternatively, a silicon substrate or a PET (polyethylene terephthalate) film may be used as the substrate 11. The shape of the substrate 11 is not particularly limited, but in this embodiment, it has a planar shape (rectangular parallelepiped shape) that is rectangular when viewed from above.

[0039] Photonic crystal 12 is formed (placed) on substrate 11. The outer shape of photonic crystal 12 is processed to be circular. The detailed structure of photonic crystal 12 will be explained with reference to FIGS.

[0040] An adjustment mechanism (not shown) is provided on the XY-axis stage 31. The adjustment mechanism is a drive mechanism such as a servo motor or a focusing handle, and adjusts the relative positional relationship between the irradiation position of the irradiation light L1 and the XY-axis stage 31 in response to a command from the control device 5.

[0041] The silicon sheet 32 ​​has a circular opening so as to expose the circularly processed photonic crystal 12. The silicon sheet 32 ​​is provided to improve adhesion between the ion sensor 1 (more specifically, the substrate 11) and the resin frame 33. Note that the shapes of the photonic crystal 12 and the opening of the silicon sheet 32 ​​are not limited to circles.

[0042] The resin frame 33 has a circular opening, similar to the silicon sheet 32. The resin frame 33 is provided to fix the ion sensor 1 onto the XY axis stage 31 with screws (not shown) in a state where the silicon sheet 32 ​​is sandwiched between the ion sensor 1 and the resin frame 33.

[0043] Fig. 3 is an enlarged perspective view schematically showing the ion sensor 1. Fig. 4 is a cross-sectional view of the ion sensor 1 taken along line IV-IV shown in Fig. 3. With reference to Figs. 3 and 4, the photonic crystal 12 is a two-dimensional photonic crystal extending in the horizontal direction (XY plane direction). A plurality of periodically arranged holes (vacant spaces) h are formed in the photonic crystal 12. The photonic crystal 12 also includes a resin 121 and metal oxide nanoparticles 122.

[0044] The refractive index of the photonic crystal 12 in the visible range is higher than the refractive index in the visible range of the main component (water in this example) of the liquid sample SPL dropped onto the ion sensor 1. Note that the magnitude relationships and numerical values ​​of the refractive indices described below are all in the visible range.

[0045] <Photonic crystal structure> It is conceivable to use precision processing techniques such as lithography or electron beam lithography to fabricate photonic crystals. However, these techniques require expensive exposure equipment. Therefore, in order to mass-produce photonic crystals, a number of exposure equipment corresponding to the production volume must be prepared, which may increase manufacturing costs. In this embodiment, to reduce manufacturing costs, photonic crystals are manufactured using nanoimprint lithography (NIL) technology. Hereinafter, nanoimprint lithography will also be abbreviated as "nanoimprint." In nanoimprinting, a mold, which is a template, is first prepared.

[0046] Fig. 5 is a scanning electron microscope (SEM) image of the mold. Fig. 6 is a view showing an atomic force microscope (AFM) image of the mold. From the images shown in Figs. 5 and 6, it can be seen that a pillar array, in which a plurality of pillars 7 are periodically arranged (more specifically, in a hexagonal close-packed structure), is formed on the mold 6.

[0047] Figure 7 is a diagram illustrating the cross-sectional shape of the pillar array formed in the mold 6. Cross-sectional views of the pillar array taken along lines VIIB-VIIB, VIIC-VIIC, and VIID-VIID shown in Figure 7A are shown in Figures 7B to 7D, respectively. Referring to Figures 7B to 7D, it can be seen that the diameter of each pillar 7 is approximately 210 nm and the height of each pillar 7 is approximately 170 nm.

[0048] Fig. 8 shows an SEM image of the photonic crystal 12. Fig. 8A shows a top view image of the photonic crystal 12 at a magnification of 10,000 times, and Fig. 8B shows a top view image of the photonic crystal 12 at a magnification of 50,000 times. Fig. 8C shows a cross-sectional image of the photonic crystal 12. Fig. 9 shows an AFM image of the photonic crystal 12. Figs. 8A to 8C and 9 confirm that although some of the locations where holes h should be formed are missing, overall a hole array corresponding to the pillar array of the mold 6 has been formed.

[0049] 10 is a diagram illustrating the cross-sectional shape of a hole array formed in photonic crystal 12. Cross-sectional views of the hole array taken along lines XB-XB, XC-XC, and XD-XD shown in FIG. 10A are shown in FIGS. 10B to 10D, respectively. It can be seen from FIGS. 10B to 10D that each of the multiple holes h has a tapered shape in which the diameter decreases from the top to the bottom of photonic crystal 12. It can also be seen that the diameter of each hole h is approximately 268 nm, and the depth of each hole h is approximately 140 nm.

[0050] <Detection principle of ion sensor> The photonic crystal 12 (resin 121) contains an ionophore and a dye as components for detecting ions (cations) that are the target substances (see FIG. 12). As will be described in detail later, an ionophore is a molecule (ion recognition molecule) that can recognize and extract specific ions. A dye is a molecule that changes its color (more specifically, the wavelength of light that it absorbs) when an ion is extracted by the ionophore. In the ion sensor 1 according to this embodiment, cations in the liquid sample SPL are optically detected by combining the change in the reflection spectrum of the photonic crystal 12 caused by the extraction of cations by the ionophore (see FIG. 11) and the change in the absorption spectrum of the dye at that time (see FIG. 12).

[0051] Figure 11 is a conceptual diagram for explaining the principle of detecting a target substance based on changes in the reflection spectrum of photonic crystal 12. For comparison, Figures 11A to 11C show a photonic crystal 8 that does not contain metal oxide nanoparticles. Figure 11D shows photonic crystal 12 according to this embodiment.

[0052] Generally, when light is incident on the boundary surface between two materials with different refractive indices, part of the incident light undergoes Fresnel reflection. When light is incident from a material with a high refractive index to a material with a low refractive index, free-end reflection occurs, in which the phase of the light does not change. Conversely, when light is incident from a material with a low refractive index to a material with a high refractive index, fixed-end reflection occurs, in which the phase of the light is shifted to the opposite phase.

[0053] 11A, the refractive index of the photonic crystal 8 is higher than that of the liquid sample SPL. Therefore, when light is irradiated onto the photonic crystal 8 onto which the liquid sample SPL has been dropped, part of the irradiated light undergoes fixed-end reflection at the interface between the liquid sample SPL and the photonic crystal 8. A part of the light that enters the inside of the photonic crystal 8 without undergoing fixed-end reflection undergoes free-end reflection at another interface. As a result of this reflection, the light reflected at the fixed end and the light reflected at the free end constructively interact with each other in the photonic crystal 8 at wavelengths that satisfy the Bragg condition (thin film interference). Therefore, when the reflection spectrum is measured, a peak appears at a specific wavelength.

[0054] 11B, when the target substance ANL is present near the interface between the photonic crystal 12 and the liquid sample SPL, the refractive index near the interface (on the liquid sample SPL side) changes due to the influence of the target substance ANL, compared to when the target substance ANL is not present near the interface (see FIG. 11A). This causes a change in the peak wavelength that satisfies the Bragg condition (peak shift) and a change in the peak intensity. Therefore, the target substance ANL can be detected by monitoring the peak change in the reflection spectrum.

[0055] More specifically, the peak wavelength of the reflection spectrum is determined by the refractive index n phC When the detection target substance ANL is not present near the interface between the photonic crystal 12 and the liquid sample SPL (see FIG. 11A), the peak of the reflection spectrum is determined by the difference in refractive index n PhC and the refractive index n of the main component of the liquid sample SPL (water in this example). SPL The difference between ΔnA(=n PhC -n SPL ) is determined according to the

[0056] On the other hand, when the detection target substance ANL is present near the boundary surface (see FIG. 11B), the peak of the reflection spectrum is at the refractive index n PhC and the average refractive index of the surrounding area, n ave The difference between ΔnB(=n PhC -n ave ), where the average refractive index n ave Conceptually, for example, n ave =n SPL ×X SPL +n ANL ×X ANL In other words, the average refractive index n ave is the refractive index n of the main component of the liquid sample SPL SPL The volume ratio X of the main component of the liquid sample SPL to the space near the boundary surface on the liquid sample SPL side is SPL and the refractive index n of the substance to be detected ANL The volume ratio of the detected substance ANL to the above space is X ANL It is calculated by adding the value obtained by multiplying by .

[0057] The larger the difference (=ΔnB-ΔnA) between the refractive index difference ΔnA when the target substance ANL is not present near the boundary surface and the refractive index difference ΔnB when the target substance ANL is present near the boundary surface, the larger the peak change in the reflection spectrum becomes. This makes it possible to detect the target substance ANL with high accuracy.

[0058] Conversely, when the size of the detection target substance ANL is small (see FIG. 11C), the ratio X of the volume that the detection target substance ANL occupies to the space near the boundary surface is smaller than when the size of the detection target substance ANL is large (see FIG. 11B). ANL The proportion of detected substance ANL is low. ANL As the average refractive index n ave Since the refractive index difference ΔnB(= nPhC -n ave ) becomes smaller. As a result, the difference in refractive index (= ΔnB - ΔnA) becomes smaller, and the peak change in the reflection spectrum becomes smaller. In this way, the smaller the size of the detection target substance ANL, the more difficult it is to detect the detection target substance ANL.

[0059] The refractive index of water, which is the main component of the liquid sample SPL, is approximately 1.3. When the main component of the photonic crystal 8 is resin 121 (for example, vinyl chloride), its refractive index is approximately 1.5. Therefore, the difference in refractive index ΔnA between the materials on either side of the boundary surface is 0.2. Even when the difference in refractive index ΔnA is small like this, if the target substance ANL is a polymer such as DNA or an antibody, it is possible to detect the target substance ANL according to the above-mentioned principle. However, when the target substance ANL is an ion (cation), its size is so small that no significant change in the peak of the reflection spectrum is obtained. Therefore, detecting ions is difficult.

[0060] Therefore, in this embodiment, as shown in FIG. 11D, metal oxide nanoparticles 122 are contained in addition to resin 121 as the base material of photonic crystal 12. Specific examples of metal oxides include zirconium oxide (ZrO2) and titanium (IV) oxide (TiO2). These metal oxides have a refractive index higher than 2.0. Therefore, when photonic crystal 12 contains metal oxide nanoparticles 122, the difference in refractive index ΔnA (= nPhC -n SPLAs a result, the difference in refractive index (= ΔnB - ΔnA) increases, which increases the peak change in the reflection spectrum, making it possible to detect the target substance ANL even if it is an ion.

[0061] Fig. 12 is a conceptual diagram illustrating the principle of ion detection based on changes in the absorption spectrum of a dye. As shown in Fig. 12, photonic crystal 12 contains resin 121, metal oxide nanoparticles 122, and a plasticizer (not shown) for resin 121. Ionophore 123, dye 124, and anion 125 are dissolved in this plasticizer.

[0062] The ionophore 123 is a lipid-soluble ion recognition molecule, which is valinomycin in this embodiment (see FIG. 17). The ionophore 123 recognizes the cation M, which is the detection target substance ANL in this embodiment. + selectively binds to cation M + By increasing the permeability of + is extracted into the photonic crystal 12.

[0063] The dye 124 is a fat-soluble cationic dye, which is KD-M11 in this embodiment (see FIG. 16). The dye 124 reacts with protons (hydrogen ions, H + In the liquid sample SPL, cations M + If cation M is present, + is extracted into the ionophore 123. At the same time, the dye 124 is deprotonated and the proton H + is released into the liquid sample SPL. When the dye 124 is deprotonated, the absorption spectrum of the dye 124 changes compared to when the dye 124 is protonated.

[0064] The anion 125 is a lipid anion, and in this embodiment, it is tetrakis[3,5-bis(trifluoromethyl)phenyl]borate sodium salt dihydrate (TFPB). The anion 125 is added to balance the charge in the photonic crystal 12 during the protonation / deprotonation of the dye 124.

[0065] In general, photonic crystals can be fabricated using only either resin (and its plasticizer) or metal oxide nanoparticles as the base material. However, if only resin is used, it is difficult to detect ions, which are minute substances, for the reasons explained in FIG. 11. On the other hand, if only metal oxide nanoparticles are used, the ionophore and dye are not supported on the metal oxide nanoparticles, and the detection principle explained in FIG. 12 does not hold. In this embodiment, resin 121 and metal oxide nanoparticles 122 are mixed. This increases the refractive index of the photonic crystal 12 by the metal oxide nanoparticles 122, enabling the detection of minute substances, and the ionophore 123 and dye 124 are dissolved in the resin 121 (plasticizer), thereby establishing the above-mentioned detection principle.

[0066] 11, it has been explained that the change in the peak of the reflection spectrum occurs due to a change in the refractive index on the surface of the photonic crystal 12 (on the liquid sample SPL side of the interface between the photonic crystal 12 and the liquid sample SPL). On the other hand, by incorporating an ionophore 123 into the photonic crystal 12 as shown in FIG. 12, a change in the refractive index also occurs inside the photonic crystal 12.

[0067] Cation M +When a liquid sample SPL containing cations M is dropped onto the ion sensor 1, if the wavelength at which a peak shift in the reflection spectrum occurs due to a change in the refractive index of the photonic crystal 12 and the wavelength at which a peak shift in the absorption spectrum occurs due to protonation / deprotonation of the dye 124 are close to each other (overlap), the intensity of the reflected light L2 obtained from the ion sensor 1 changes significantly. Therefore, by analyzing the reflection spectrum of the ion sensor 1, it is possible to determine the amount of cations M in the liquid sample SPL. + The spectrum measurement results of the ion sensor 1 will be described in detail from FIG.

[0068] <Combination of resin and metal oxide nanoparticles> Depending on the combination of resin 121 and (dispersion of) metal oxide nanoparticles 122, there is a possibility that metal oxide nanoparticles 122 may not be uniformly dispersed in resin 121 or that resin 121 may not dissolve. Therefore, as will be described below, prior to fabrication of photonic crystal 12, several combinations of resin 121 and metal oxide nanoparticles 122 were prepared, mixed, and each mixed solution was evaluated.

[0069] Fig. 13 is a diagram for explaining the combination of resin 121 and metal oxide nanoparticles 122. Fig. 13 shows the combination of materials and the weight ratio of those materials as the compositions of six types of mixed liquids (first to sixth mixed liquids).

[0070] The first mixture liquid contained a zirconium oxide (ZrO2) dispersion, polyvinyl chloride (PVC), and the plasticizer 2-nitrophenyl octyl ether (NPOE). The zirconium oxide dispersion was a methyl ethyl ketone (MEK) dispersion (SZR-K, manufactured by Sakai Chemical Industry Co., Ltd.) containing 30 wt% zirconium oxide nanoparticles. Hereinafter, the zirconium oxide nanoparticles will also be referred to as "ZrO2 nanoparticles." The particle diameter of each ZrO2 nanoparticle was 3 to 5 nm. The weight ratio of these materials was ZrO2 nanoparticles:PVC:NPOE:MEK = 6:4:2:3.

[0071] The second mixture was a liquid containing a rutile titanium dioxide (TiO2) dispersion, PVC, and NPOE. The rutile titanium dioxide dispersion was a methanol dispersion (SRD-M, manufactured by Sakai Chemical Industry Co., Ltd.) containing 15 wt% rutile titanium dioxide nanoparticles. Hereinafter, the rutile titanium dioxide nanoparticles will also be referred to as "TiO2 nanoparticles." The particle diameter of each TiO2 nanoparticle was 6 to 8 nm. The weight ratio of the materials contained in the second mixture was TiO2 nanoparticles:PVC:NPOE:methanol = 6:4:2:3.

[0072] The third mixture was a liquid containing a zirconium oxide dispersion, PVC, NPOE, and tetrahydrofuran (THF). The weight ratio of the materials contained in the third mixture was ZrO nanoparticles:PVC:NPOE:THF = 6:4:2:3.

[0073] The fourth mixture was a liquid containing a rutile titanium dioxide dispersion, PVC, NPOE, and THF. The weight ratio of the materials contained in the fourth mixture was TiO nanoparticles:PVC:NPOE:THF=6:4:2:3.

[0074] The fifth mixed solution was a liquid containing a zirconium oxide dispersion, a vinyl chloride-vinyl acetate-vinyl alcohol copolymer (PVC-VAC-VA: poly(vinyl chloride-co-vinyl acetate-co-vinyl alcohol)), NPOE, and MEK. PVC-VAC-VA is a copolymer (manufactured by Sigma-Aldrich) of vinyl chloride (VC), vinyl acetate (VAC), and vinyl alcohol (VA). The weight ratio of the materials contained in the fifth mixed solution was ZrO2 nanoparticles:PVC-VAC-VA:NPOE:MEK = 6:4:2:3.

[0075] The sixth mixture contained a rutile titanium dioxide dispersion, PVC-VAC-VA, NPOE, and methanol. The weight ratio of the materials in the fifth mixture was TiO nanoparticles:PVC-VAC-VA:NPOE:methanol = 6:4:2:3.

[0076] 14A and 14B show the state of each of the mixed solutions shown in FIG. 13. As shown in FIGS. 14A and 14B, PVC did not dissolve in the first and second mixed solutions. In other words, the resin 121 and the dispersion of metal oxide nanoparticles 122 were not sufficiently mixed. Therefore, it was found that the first and second mixed solutions were not suitable for producing photonic crystals 12.

[0077] Both the third and fourth mixed solutions contain THF, which is known to be capable of dissolving PVC. In the third mixed solution, the PVC dissolved, but the ZrO2 nanoparticles aggregated (see Figure 14C). Conversely, in the fourth mixed solution, the TiO2 particles did not aggregate, but the PVC did not dissolve sufficiently (see Figure 14D). Therefore, it was found that the third and fourth mixed solutions are also unsuitable for fabricating the photonic crystal 12.

[0078] The fifth and sixth mixed solutions were prepared by using PVC-VAC-VA instead of PCV. Observation of the fifth mixed solution confirmed that PVC-VAC-VA was fully dissolved and that ZrO2 nanoparticles were uniformly dispersed (see Figure 14E). On the other hand, in the sixth mixed solution containing TiO2 nanoparticles, PVC-VAC-VA did not dissolve (see Figure 14F).

[0079] From the above evaluation results, it was found that, among the first to sixth mixed solutions, only the fifth mixed solution can be suitably used for producing a photonic crystal.

[0080] <Spectral measurement results> Various dyes may be used. In this embodiment, a dye called KD-M11 is used, but the following explanation will be made in comparison with the case where a dye called NCODE is used. As mentioned above, valinomycin, which is known to have high selectivity for potassium ions, was used as the ionophore 123.

[0081] Figure 15 is a diagram showing the structural formula of NCODE, Figure 16 is a diagram showing the structural formula of KD-M11, and Figure 17 is a diagram showing the structural formula of valinomycin.

[0082] As explained in Figures 11 and 12, in order to make the peak change in the reflection spectrum of the ion sensor 1 noticeable, the wavelength range in which the peak change in the reflection spectrum occurs due to the change in refractive index of the photonic crystal 12 and the wavelength range in which the peak change in the absorption spectrum occurs due to the protonation / deprotonation of the dye 124 must be close to (overlap) each other.

[0083] Fig. 18 is a diagram showing the reflection spectrum of the photonic crystal fabricated using the fifth mixed liquid, in which the horizontal axis represents the wavelength of light and the vertical axis represents the reflection intensity.

[0084] The spectrum labeled "with ZrO2 nanoparticles" is the measurement result of the reflectance spectrum of a photonic crystal containing ZrO2 nanoparticles (but not containing ionophore 123 or dye 124) made using the fifth mixed solution. On the other hand, the spectrum labeled "without ZrO2 nanoparticles" is the measurement result of the reflectance spectrum of a photonic crystal made from PVC that does not contain ZrO2 nanoparticles (also not containing ionophore 123 or dye 124). No liquid sample SPL was dripped onto these photonic crystals.

[0085] No clear reflection peak was observed in the photonic crystal without ZrO2 nanoparticles. In contrast, a reflection peak located near 640 nm was confirmed in the photonic crystal with ZrO2 nanoparticles. This is thought to be because, as explained in Figure 11, the refractive index of the photonic crystal was significantly increased by incorporating ZrO2 nanoparticles into the photonic crystal substrate. The measurement results shown in Figure 18 indicate that it is now possible to measure the reflection spectrum even when using an aqueous solution as the liquid sample SPL.

[0086] Figure 19 shows the absorption spectrum of NCODE. Figure 20 shows the absorption spectrum of KD-M11. In Figures 19 and 20, the horizontal axis represents the wavelength of light, and the vertical axis on the left represents the absorption intensity. For comparison, the reflection spectrum of a photonic crystal containing ZrO2 nanoparticles (see Figure 18) is also shown (see the vertical axis on the right).

[0087] 19 and 20, the spectrum labeled "protonated" is the result of measuring the absorption spectrum when the dye 124 is in a protonated state. The protonation of the dye 124 is achieved, for example, by introducing 10 mM hydrogen chloride (HCl) into the dye 124. The spectrum labeled "deprotonated" is the result of measuring the absorption spectrum when the dye 124 is in a deprotonated state. The deprotonation of the dye 124 is achieved, for example, by introducing 10 mM potassium hydroxide (KOH) into the dye 124.

[0088] As explained in FIG. 12, the cation M + When a liquid sample SPL containing cation M is dropped onto the ion sensor 1, the dye 124 is protonated, and the ionophore 123 is charged with cation M. + The deprotonated state of the dye 124 corresponds to the state where the ionophore 123 is not extracted. + corresponds to the extracted state.

[0089] When dye 124 is NCODE, the peak wavelength of the absorption spectrum of protonated NCODE is not located in the visible range. The peak wavelength of the absorption spectrum of deprotonated NCODE is within the visible range, but is located at the edge (near 430 nm). Comparing the peak of the absorption spectrum of deprotonated NCODE with the peak of the reflection spectrum of a photonic crystal containing ZrO2 nanoparticles, there is almost no overlap between the two.

[0090] In contrast, when dye 124 is KD-M11, the peak wavelength of the absorption spectrum of protonated KD-M11 is located near 430 nm. The peak wavelength of the absorption spectrum of deprotonated KD-M11 is located near 610 nm. It can be seen that the wavelength range including the peak wavelength of the absorption spectrum of deprotonated KD-M11 (≒610 nm) and the wavelength range including the peak wavelength of the reflection spectrum of the photonic crystal containing ZrO2 nanoparticles (≒640 nm) do not completely coincide, but there is sufficient overlap.

[0091] In order to clarify the characteristics of the ion sensor 1 according to this embodiment, the results of measuring the reflection spectrum of the ion sensor 1 will be described along with the results of measuring the reflection spectrum of two types of ion sensors according to comparative examples.

[0092] FIG. 21 is a diagram illustrating the composition of the photonic crystal 12 in each of the three types of ion sensors. Referring to FIG. 21, the photonic crystal 12 constituting the ion sensor 1 according to the present embodiment contains KD-M11 (see FIG. 16) as the dye 124 and valinomycin (see FIG. 17) as the ionophore 123, as described in FIG. 12. In contrast, the photonic crystal constituting the ion sensor according to Comparative Example 1 contains KD-M11 but does not contain the ionophore 123. Meanwhile, the photonic crystal constituting the ion sensor according to Comparative Example 2 contains valinomycin but contains NCODE (see FIG. 15) as the dye 124 instead of KD-M11. The weight ratios or amounts of substances of these materials are as shown in FIG. 21. The configurations of the ion sensors according to Comparative Examples 1 and 2, other than those described above, are the same as the configuration of the ion sensor 1 according to the present embodiment.

[0093] Fig. 22 is a diagram summarizing the measurement results of the reflection spectrum of the ion sensor according to Comparative Example 1. Fig. 23 is a diagram summarizing the measurement results of the reflection spectrum of the ion sensor according to Comparative Example 2. Fig. 24 is a diagram summarizing the measurement results of the reflection spectrum of the ion sensor according to the present embodiment.

[0094] In Figures 22 to 24, there are six concentrations (1 × 10 -5 M, 1 x 10 -4 M, 1 x 10 -3 M, 1 x 10 -2 M, 1 x 10 -1 Potassium chloride (KCl) solutions (1M, 1M) were prepared as liquid samples SPL. The hydrogen ion concentrations of these solutions were adjusted to pH 6.

[0095] The horizontal axis in Figures 22 to 24 represents the concentration of the solution on a logarithmic scale. The vertical axis represents the normalized reflection intensity. The values ​​on the vertical axis are calculated as follows: The reflection spectra of six potassium chloride solutions with different concentrations are measured in order, and the peak intensity is determined for each of the six measured reflection spectra. The six peak intensities determined are designated I1 to I6, and the maximum peak intensity among the peak intensities I1 to I6 is designated Imax. The reflection intensity is normalized by dividing the peak intensities I1 to I6 by the maximum peak intensity Imax.

[0096] First, referring to Figure 22, Comparative Example 1, which does not contain ionophore 123, basically showed a tendency for the reflection intensity to increase as the potassium ion concentration in the liquid sample SPL increased. According to the detection principle explained in Figure 12, even if ionophore 123 was not present, the cation M + (potassium ions) are extracted into the photonic crystal, the cation M + The higher the concentration of cation M + It is thought that the amount of extracted cation M will also increase. Accordingly, the deprotonation of the dye 124 (KD-M11) will progress, and the absorption intensity of the dye 124 will increase, so the reflection intensity should decrease accordingly. However, the measurement results shown in FIG. 22 show that no decrease in reflection intensity occurs. Thus, from the measurement results of Comparative Example 1, it can be seen that if the ionophore 123 is not contained in the photonic crystal, the amount of extracted cation M + It can be said that this confirms that is not extracted into the photonic crystal.

[0097] 22, the higher the concentration of cation M+, the greater the reflection intensity. There are various possible reasons for this, but they will not be explained here.

[0098] 23, in Comparative Example 2, which contains a dye 124 (NCODE) different from that of the present embodiment, a tendency for the reflection intensity to decrease slightly as the potassium ion concentration increases was confirmed. In Comparative Example 2, because it contains ionophore 123 (valinomycin), the amount of potassium ions extracted increases as the potassium ion concentration increases, increasing the absorption intensity by NCODE and decreasing the reflection intensity.

[0099] However, as explained in Figure 19, there is almost no overlap in the wavelength range including the peak wavelength between the absorption spectrum of deprotonated NCODE and the reflection spectrum of the photonic crystal containing ZrO2 nanoparticles, so the decrease in reflection intensity is relatively small.

[0100] 24, in the present embodiment, it was confirmed that the reflection intensity tends to decrease as the potassium ion concentration increases, similar to Comparative Example 2. The reason for this is the same as that described above in Comparative Example 2.

[0101] Furthermore, in this embodiment, KD-M11 is contained as the dye 124 instead of NCODE. The wavelength range including the peak wavelength in the absorption spectrum of deprotonated KD-M11 and the wavelength range including the peak wavelength in the reflection spectrum of the photonic crystal including ZrO2 nanoparticles overlap well (see FIG. 20). Therefore, compared to Comparative Example 2, the absorption intensity by the dye 124 is higher, and the amount of decrease in reflection intensity is correspondingly larger.

[0102] In this embodiment, as a further control experiment, measurements were also carried out using a sodium chloride (NaCl) solution as the liquid sample SPL. The concentration and pH of the sodium chloride solution were the same as those of the potassium chloride solution described above. As shown in FIG. 24, a tendency was observed in which the reflection intensity increased as the sodium ion concentration increased. Comparing the measurement results for sodium ions with those for potassium ions confirms that the ion sensor 1 according to this embodiment functions as a sensor capable of selectively detecting potassium ions.

[0103] In the measurement results shown in Figure 24, the reflection intensity at 1M, which has the highest sodium ion concentration, is 1×10 -5 The reflection intensity is lower than that at M. This is presumably because when the sodium ion concentration becomes considerably high, even sodium ions are extracted by ionophore 123 (valinomycin).

[0104] <Ion sensor manufacturing flow> Fig. 25 is a flowchart for explaining a manufacturing method of the ion sensor 1 according to this embodiment. Fig. 26 is a schematic process diagram of the manufacturing method of the ion sensor 1 according to this embodiment. Generally, nanoimprinting is broadly divided into thermal nanoimprinting, optical nanoimprinting, and room temperature nanoimprinting, and this embodiment employs room temperature nanoimprinting. Known room temperature nanoimprinting methods include droplet coating and spin coating, and this embodiment employs droplet coating.

[0105] 25 and 26, a mold (casting die) 6 to be used for nanoimprinting is prepared in step (hereinafter, step will be abbreviated as "S") 1. Mold 6 is made of polydimethylsiloxane (PDMS), which is a liquid silicone rubber.

[0106] Specifically, the mold 6 can be fabricated by the following procedure. First, a hole array 9 is fabricated by electron beam lithography or dry etching. A mixture of PDMS prepolymer (SILPOT 184, manufactured by Dow Corning Toray Co., Ltd.) and a catalyst (SILPOT 184 CAT, manufactured by Dow Corning Toray Co., Ltd.) before curing is stirred and poured into a frame (not shown) surrounding the hole array 9. The mixture is then degassed for a predetermined time (e.g., one hour). The PDMS prepolymer and catalyst mixture is then further poured into the mold until a sufficient thickness is achieved (see FIG. 26A). The PDMS prepolymer and catalyst mixture is then baked together with the hole array 9 under predetermined conditions. For example, the PDMS is cured to a certain extent by heating at 70°C for one hour, and the hole array 9 is then released (see FIG. 26B). The PDMS is then cured by heating at 150°C for another hour. The baked PDMS is processed into a predetermined size (in this embodiment, a circle with a diameter of 13 mm).

[0107] In S2, a "fifth mixed solution" is prepared, which is a mixed solution containing resin 121, ZrO2 nanoparticles 122, and a plasticizer (containing ionophore 123, dye 124, anion 125, etc.). The composition of the fifth mixed solution has been described in detail in FIG. 13 or FIG. 21, and therefore will not be described again here.

[0108] In S3, the substrate 11 is washed. If the substrate 11 is a cover glass, for example, the substrate 11 is immersed in acetone and ultrasonically cleaned for a predetermined time (for example, 20 minutes). The substrate 11 is then washed with ethanol, and thereafter, the substrate 11 is further washed with distilled water. This allows impurities (such as organic matter) adhering to the substrate 11 to be removed.

[0109] In S4, the fifth mixed liquid prepared in S2 is dropped onto the substrate 11 (see FIG. 26C). The amount of the fifth mixed liquid dropped may be a very small amount (75 μL in this example).

[0110] In S5, a nanoimprinting apparatus (not shown) is used to press the mold 6 prepared in S1 onto the fifth liquid mixture from above, thereby transferring the shape of the mold 6 to the fifth liquid mixture (see FIG. 26D). Because PDMS is a soft material, applying excessive pressure may damage the mold 6. Therefore, the lower limit of the pressure range of the nanoimprinting apparatus (model EUN-4200, manufactured by Engineering Systems Co., Ltd.) can be used to apply as little pressure as possible. In this embodiment, the pressure applied to the mold 6 was set to 0.68 MPa, and the time for pressing the mold 6 was set to 20 minutes. PDMS is gas permeable. Therefore, while the mold 6 is being pressed, the solvent of the fifth liquid mixture (e.g., methyl ethyl ketone, which is the dispersion medium for ZrO2 nanoparticles) evaporates, causing the fifth liquid mixture to solidify.

[0111] In S6, the mold 6 is removed (see FIG. 26E), thereby completing the ion sensor 1 and completing the series of processes.

[0112] As described above, according to this embodiment, since the resin 121 contains PVC-VAC-VA, the ZrO2 nanoparticles can be uniformly dispersed in the resin 121. This makes it possible to fabricate a photonic crystal 12 with a high refractive index and in which ZrO2 nanoparticles are dispersed. Furthermore, each ZrO2 nanoparticle has a size on the order of a single nanometer (3 to 5 nm in this example), which is particularly small among nanoparticles. This makes it difficult for light scattering to occur even when the ZrO2 nanoparticles are contained in the resin 121, and whitening of the photonic crystal 12 can be suppressed.

[0113] Furthermore, according to this embodiment, KD-M11 is selected as the dye 124. The peaks of the reflection spectrum of the photonic crystal containing ZrO2 nanoparticles and the absorption spectrum of KD-M11 overlap well. This results in a significant change in the peak of the reflection spectrum, making it possible to realize an ion sensor 1 capable of detecting minute ions.

[0114] In this embodiment, an example in which zirconium oxide nanoparticles (ZrO nanoparticles) are used as a specific example of metal oxide nanoparticles contained in the ion sensor has been described, but other nanoparticles (titanium oxide nanoparticles, barium titanate nanoparticles, etc.) may also be used. When other metal oxide nanoparticles are used, a material capable of dispersing the nanoparticles is appropriately used.

[0115] [Variations] In the following modified examples, a configuration for detecting taste substances such as sucrose or saccharin sodium instead of ions (cations) will be described. The configuration of the taste substance sensor 1A (see FIGS. 2 and 3) differs from the configuration of the ion sensor 1 described in the embodiment in that it contains a lipid instead of an ionophore and that the inclusion of a dye is not essential. The other configurations of the taste substance sensor 1A are the same as those of the ion sensor 1, so detailed description will not be repeated. Furthermore, the configuration of the taste substance detection system 100A (see FIG. 1) is the same as that of the ion detection system 100, except that it includes the taste substance sensor 1A instead of the ion sensor 1.

[0116] Fig. 27 shows the composition of a tastant sensor 1A for detecting sucrose. Fig. 28 shows the composition of a tastant sensor 1A for detecting saccharin sodium. Fig. 29 shows the structural formulas of a tastant, a lipid used for detecting the tastant, and a plasticizer of the resin 121 in this modified example.

[0117] 27 to 29, palmitic acid (PA) and TDAB (1,3,5-tris(diphenylamino)benzene) can be used as lipids for selectively adsorbing sucrose and recognizing only sucrose. TDAB can be used as lipids for selectively adsorbing saccharin sodium and recognizing only saccharin sodium. Furthermore, dioctyl phenylphosphonate (DOPP) can be used as a plasticizer. The method for manufacturing the taste substance sensor 1A is the same as the method for manufacturing the ion sensor 1 described with reference to FIGS. 25 and 26. The resin 121 contains PVC. As described above, the photonic crystal 12 of the taste substance sensor 1A, unlike the photonic crystal 12 of the ion sensor 1, does not contain the dye KDM-11.

[0118] Next, we will explain the evaluation results of the optical properties of the taste substance sensor 1A. First, sucrose solutions and saccharin sodium solutions, each adjusted to different concentrations, were prepared. The following measurements were performed using these solutions. The solutions were dropped onto the taste substance sensor 1A. After dropping, the sensor was left for one minute, after which the solution was removed and the taste substance sensor 1A was dried. The reflection spectrum of the taste substance sensor 1A was then measured before and after dropping the solutions. Furthermore, a calibration curve was created based on the change in the reflection spectrum (change in the reflection peak intensity).

[0119] Fig. 30 shows the results of measuring the reflection spectrum when sucrose solutions of different concentrations are dropped. In Fig. 30 and Fig. 32 described below, the horizontal axis represents the wavelength of light, and the vertical axis represents the reflection intensity.

[0120] The concentrations of the sucrose solutions (sucrose concentrations) were 0 mM, 5 mM, 10 mM, 50 mM, 100 mM, 500 mM, and 1,000 mM. As shown in Figure 30, the peak intensity of the reflection spectrum decreased as the sucrose concentration increased. This is because the lipids in the taste substance sensor 1A selectively adsorbed or extracted sucrose, changing the refractive index within the taste substance sensor 1A.

[0121] The reflection spectrum marked "wash" in Figure 30 was obtained by washing the surface of the taste substance sensor 1A with ultrapure water after measurement with the 1,000 mM solution, and then measuring the reflection spectrum again. The reflection spectrum in this case roughly coincided with the reflection spectrum before the solution was added (marked "bare"), confirming that the reflection spectrum was restored by washing the surface.

[0122] FIG. 31 is a diagram showing the relationship between the reflection peak intensity shown in FIG. 30 and the sucrose concentration. In FIG. 31, the horizontal axis represents the sucrose concentration dropped onto the taste substance sensor 1A. The vertical axis represents the peak intensity of the reflection spectrum (hereinafter abbreviated as "reflection intensity"). FIG. 31 shows that the measurement results of the reflection intensity are plotted on the same line, in other words, the calibration curve shows good linearity.

[0123] Figure 32 shows the results of measuring the reflectance spectrum when saccharin sodium solutions of different concentrations were dropped. Referring to Figure 32, the concentrations of the saccharin sodium solutions (saccharin sodium concentrations) were 0 μM, 1 μM, 10 μM, 100 μM, 1,000 μM, and 10,000 μM. As with the sucrose solution, the peak intensity of the reflectance spectrum decreased with increasing saccharin sodium concentration. This mechanism is similar to the mechanism described above for the sucrose solution.

[0124] The reflectance spectrum marked with "wash" in Fig. 32 was obtained by washing the surface of the taste substance sensor 1A with a saturated aqueous sodium bicarbonate solution after measurement with a 10 μM solution, and then measuring the reflectance spectrum again. It was also confirmed that the reflectance spectrum recovered after surface washing for saccharin sodium.

[0125] Fig. 33 is a diagram showing the relationship between the reflection intensity shown in Fig. 32 and the saccharin sodium concentration. In Fig. 33, the horizontal axis represents the saccharin sodium concentration dropped onto the taste substance sensor 1A, and the vertical axis represents the reflection intensity. Referring to Fig. 33, it can be seen that the calibration curve also shows relatively good linearity for the saccharin sodium solution.

[0126] Fig. 34 shows the results of creating a calibration curve for sucrose in this modified example. Fig. 35 shows the results of creating a calibration curve for sucrose in a comparative example. Fig. 34 shows four calibration curves obtained from four samples (taste substance sensors 1A) prepared under the same conditions. On the other hand, Fig. 35 shows two calibration curves obtained from a taste substance sensor that uses cycloolefin polymer (COP) instead of PVC and uses the physical adsorption of sucrose to COP as its detection principle.

[0127] 34 and 35, in the comparative example, the linearity of the calibration curve (the linearity of the change in reflection intensity according to the sucrose concentration) is low, and the reflection intensity does not decrease unless the sucrose concentration is sufficiently high. In contrast, in this modified example, the reflection intensity decreases linearly with increasing sucrose concentration, and the linearity of the calibration curve is good. Furthermore, the variation in the calibration curves among the four samples is small.

[0128] Figure 36 shows the results of creating a calibration curve for saccharin sodium in this modified example. Figure 37 shows the results of creating a calibration curve for saccharin sodium in the comparative example. Similarly, Figures 36 and 37 show that, while an appropriate calibration curve could not be created in the comparative example, this modified example can create a calibration curve with good linearity and little variation.

[0129] As described above, the substances to be detected that can be detected by the sensor manufactured according to the manufacturing method described in the above embodiment are not limited to ions (cations), but may also be taste substances such as sucrose or saccharin sodium.

[0130] Furthermore, to confirm that the taste substances detectable by the taste substance sensor 1A are selective for the lipids added to the photonic crystal 12, measurements were carried out in which the combinations of the types of taste substances and the types of lipids were mismatched.

[0131] Figure 38 shows the measurement results when a saccharin sodium solution is dropped onto a sucrose tastant sensor. Figure 39 shows the measurement results when an aspartame solution is dropped onto a sucrose tastant sensor. Figure 40 shows the measurement results when a sucrose solution is dropped onto a saccharin sodium tastant sensor. In each of Figures 38 to 40, (A) shows the reflection spectrum, and (B) shows the concentration dependence of the reflection intensity.

[0132] When a saccharin sodium solution or aspartame solution was dropped onto the sucrose taste substance sensor, the reflectance spectrum did not change at all (see Figures 38 and 39). Furthermore, when a sucrose solution was dropped onto the saccharin sodium taste substance sensor, the reflectance spectrum hardly changed at all unless the sucrose concentration was high (500 mM or higher). These results indicate that the combination of the type of taste substance and the type of lipid is selective.

[0133] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not by the description of the above embodiments, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0134] 1 ion sensor, 1A taste substance sensor, 2 light source, 3 holding member, 31 XY axis stage, 32 silicon sheet, 33 resin frame, 4 photodetector, 5 control device, 51 processor, 52 memory, 6 mold, 7 pillar, 9 hole array, 11 substrate, 8, 12 photonic crystal, 121 resin, 122 metal oxide nanoparticles (ZrO2 nanoparticles), 123 ionophore, 124 dye, 125 anion, 100 ion detection system, 100A taste substance detection system.

Claims

1. An ion sensor for detecting cations contained in a liquid sample, a photonic crystal onto which the liquid sample is dropped, The photonic crystal is a resin in which a plurality of holes, each having a diameter smaller than the wavelength of visible light, are periodically arranged; a plurality of metal oxide nanoparticles each having a size of a single nanometer and dispersed in the resin without being periodically arranged; The resin is an ionophore capable of selectively extracting the cation; a dye that is deprotonated when the cation is extracted into the ionophore; the reflection spectrum of the photonic crystal has a peak in the visible range, An ion sensor, wherein a wavelength range including a peak in the reflection spectrum of the photonic crystal and a wavelength range including a peak in the absorption spectrum of the dye in a deprotonated state overlap.

2. each of the plurality of metal oxide nanoparticles is a zirconium oxide nanoparticle; 2. The ion sensor according to claim 1, wherein the resin contains a copolymer of vinyl chloride, vinyl acetate, and vinyl alcohol.

3. the cation is a potassium ion, the ionophore is valinomycin; 3. The ion sensor according to claim 1, wherein the dye is KD-M11.

4. a holding member configured to hold the ion sensor according to any one of claims 1 to 3; a light source that emits the visible light for irradiating the liquid sample; a photodetector for detecting reflected light from the liquid sample; a detection device that detects the cations based on the reflected light detected by the photodetector.

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