JP2015212625A - Analytical method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an analytical method by which a target substance can be detected with high sensitivity.SOLUTION: The analytical method of the present invention includes: a step (S1) of acquiring a first reflection spectrum having a first absorption region and a second absorption region while a target substance is not deposited on a sample analysis element; a step (S2) of acquiring a second reflection spectrum having a third absorption region and a fourth absorption region while the target substance is deposited on the sample analysis element; a step (S3) of calculating a difference between a wavelength at the minimum point in the first absorption region and a wavelength at the minimum point in the third absorption region, and a difference between a wavelength at the minimum point in the second absorption region and a wavelength at the minimum point in the fourth absorption region; and a step (S4) of detecting the target substance by using absorption regions where a larger difference in the above calculated differences is obtained. A propagated surface plasmon and a localized surface plasmon electromagnetically interact, while a resonance wavelength of the propagated surface plasmon is different from a resonance wavelength of the localized surface plasmon.

Description

  The present invention relates to an analysis method.

  In recent years, demand for medical diagnosis, food inspection, and the like has been increasing, and development of a small and high-speed sensing technology has been demanded. Various types of sensors, including electrochemical techniques, have been studied. However, surface plasmon resonance (SPR) is used because it can be integrated, is low-cost, and does not choose the measurement environment. There is growing interest in sensors.

For example, Non-Patent Document 1 includes localized surface plasmon (LSP) and propagation surface plasmon (PSP).
As an example of a sensor having a structure that realizes a hybrid mode that resonates both modes with Surface Plasmon (Surface Plasma), a sensor called GSPP (Gap type Surface Plasmon Polaron) has been proposed.

OPTICS LETTERS, VOL. 34, no. 3,2009,244-246

  Here, when the target substance adheres to the sensor (sample analysis element) as described above, the wavelength of the reflection spectrum changes. An analysis method for detecting a target substance by utilizing such a change in wavelength of the reflection spectrum is known. Such an analytical method is required to detect a target substance with high sensitivity.

  One of the objects according to some embodiments of the present invention is to provide an analysis method capable of detecting a target substance with high sensitivity.

The analysis method according to the present invention includes:
A method for analyzing a target substance using a sample analysis element,
In a state where the target substance is not attached to the sample analysis element, the sample analysis element is irradiated with light to detect reflected light from the sample analysis element, and a first absorption region and the first absorption region Obtaining a first reflection spectrum having a second absorption region on the longer wavelength side,
In a state where the target substance is attached to the sample analysis element, the sample analysis element is irradiated with light, reflected light from the sample analysis element is detected, and a third absorption corresponding to the first absorption region is detected. And a fourth absorption region corresponding to the second absorption region, and at least one of the third absorption region and the fourth absorption region is long in the first absorption region or the second absorption region. Obtaining a second reflection spectrum that is shifted to the wavelength side;
The difference between the wavelength of the minimum point of the first absorption region and the wavelength of the minimum point of the third absorption region, and the difference between the wavelength of the minimum point of the second absorption region and the wavelength of the minimum point of the fourth absorption region And a step of calculating
Detecting the target substance using an absorption region having a larger difference among the calculated differences;
Including
The sample analysis element is:
A metal layer,
A dielectric layer provided on the metal layer;
A plurality of metal particles provided on the dielectric layer;
Have
The plurality of metal particles have a periodic array capable of exciting propagating surface plasmons propagating through an interface between the metal layer and the dielectric layer,
The propagation type surface plasmon and the localized type surface plasmon excited by the metal particle interact electromagnetically,
The resonance wavelength of the propagation surface plasmon is different from the resonance wavelength of the localized surface plasmon.

  In such an analysis method, the minimum point of the absorption region of the reflection spectrum before and after deposition of the target substance when a sample analysis element having the same resonance wavelength of the propagation surface plasmon and the resonance wavelength of the localized surface plasmon is used. The difference between the wavelength of the local minimum point of the first absorption region and the wavelength of the local minimum point of the third absorption region, and the wavelength of the local minimum point of the second absorption region and the wavelength of the local minimum point of the fourth absorption region One of the differences can be increased. Thus, the analysis method according to the present embodiment can increase the wavelength difference (change amount) of the minimum point of the absorption region of the reflection spectrum before and after the target substance is attached, and the absorption region having a large wavelength change amount. Since the target substance can be detected using the target substance, the target substance can be detected with high sensitivity.

In the analysis method according to the present invention,
The propagation wavelength of the propagation surface plasmon is longer than the resonance wavelength of the localized surface plasmon,
In the step of detecting the target substance,
The target substance may be analyzed using the first absorption region and the third absorption region.

  Such an analysis method can detect the target substance with high sensitivity.

In the analysis method according to the present invention,
The propagation wavelength of the propagation surface plasmon is shorter than the resonance wavelength of the localized surface plasmon,
In the step of detecting the target substance,
The target substance may be analyzed using the second absorption region and the fourth absorption region.

  Such an analysis method can detect the target substance with high sensitivity.

Sectional drawing which shows typically the sample analysis element which concerns on this embodiment. The top view which shows typically the sample analysis element which concerns on this embodiment. The figure for demonstrating the relationship between the arrangement | sequence of a metal particle, a propagation type surface plasmon, and a localized type surface plasmon. The figure which shows typically the dispersion | distribution relationship of surface plasmon polariton. The figure for demonstrating that the resonance wavelength of a propagation type surface plasmon will change when a target substance adheres to a sample analysis element. The figure for demonstrating anti-crossing. The flowchart for demonstrating the analysis method which concerns on this embodiment. The figure for demonstrating the analysis method which concerns on this embodiment. The figure for demonstrating a reflection spectrum. The figure for demonstrating a reflection spectrum. The figure for demonstrating a reflection spectrum. The figure for demonstrating a reflection spectrum. The figure for demonstrating the model used in Experimental example 1. FIG. The graph which plotted the wavelength of the minimum point of two absorption regions in a reflection spectrum when changing the diameter of Au particle | grains in the range of 80 nm-150 nm. The figure for demonstrating the model used in Experimental example 2. FIG. The figure for demonstrating the model used in Experimental example 2. FIG. Reflection spectrum when the diameter of Au particles is 80 nm. Reflection spectrum when the diameter of Au particles is 104 nm. Reflection spectrum when the diameter of Au particles is 130 nm. Reflection spectrum in a region where the diameter of Au particles is 117 nm. Reflection spectrum in a region where the diameter of Au particles is 129 nm.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. The embodiments described below do not unduly limit the contents of the present invention described in the claims. In addition, not all of the configurations described below are essential constituent requirements of the present invention.

1. Sample Analysis Element First, a sample analysis element according to the present embodiment will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing a sample analysis element 100 according to this embodiment. FIG. 2 is a plan view schematically showing the sample analysis element 100 according to this embodiment. 1 is a cross-sectional view taken along the line II of FIG. 1 and 2 illustrate the X axis, the Y axis, and the Z axis as three axes orthogonal to each other.

  As shown in FIGS. 1 and 2, the sample analysis element 100 includes a metal layer 10, a dielectric layer 20, and metal particles 30.

1.1. Metal Layer The metal layer 10 is not particularly limited as long as it provides a metal surface that does not transmit light. For example, the metal layer 10 has a shape of a film, a plate, a layer, or a film. The metal layer 10 may be provided on the substrate 2 as shown in FIG. Although it does not specifically limit as the board | substrate 2, The thing which does not affect easily the propagation type surface plasmon (PSP) excited by the interface of the metal layer 10 and the dielectric material layer 20 is preferable. The substrate 2 is, for example, a glass substrate, a silicon substrate, or a resin substrate. The planar shape (the shape seen from the Z-axis direction) of the surface on which the metal layer 10 of the substrate 2 is provided is not particularly limited.

  The metal layer 10 is formed by a technique such as vapor deposition, sputtering, casting, or machining. The metal layer 10 may be provided on the entire surface of the substrate 2 or may be provided on a part of the surface of the substrate 2. The thickness (size in the Z-axis direction) of the metal layer 10 is not particularly limited as long as PSP is excited at the interface between the metal layer 10 and the dielectric layer 20, and is, for example, 10 nm to 1 mm, preferably 20 nm or more. It is 100 μm or less, more preferably 30 nm or more and 1 μm or less.

The metal layer 10 is a metal having an electric field in which an electric field given by excitation light and a polarization induced by the electric field oscillate in opposite phases, that is, when a specific electric field is given, The real part has a negative value (has a negative dielectric constant), and the imaginary part has a dielectric constant that is smaller than the absolute value of the dielectric constant of the real part. Examples of the metal having such a dielectric constant include gold, silver, aluminum, copper, platinum, or alloys thereof. When light in the visible light region is used as excitation light, the metal layer 10 preferably includes a layer made of gold, silver, or copper. The surface of the metal layer 10 (a plane parallel to the XY plane in the illustrated example) may or may not be a specific crystal plane. The metal layer 10 may be composed of a plurality of metal layers.

  The metal layer 10 has a function of exciting the PSP in the sample analysis element 100. Specifically, when light (excitation light) enters the metal layer 10, PSP is excited at the interface between the metal layer 10 and the dielectric layer 20 (near the interface). The PSP excited at the interface between the metal layer 10 and the dielectric layer 20 can electromagnetically interact (hybridize) with the localized surface plasmon (LSP) excited by the metal particles 30.

1.2. Dielectric Layer The dielectric layer 20 is provided on the metal layer 10. The dielectric layer 20 is provided in contact with the metal layer 10. The dielectric layer 20 has a film, layer, or film shape. The dielectric layer 20 can separate the metal layer 10 and the metal particles 30. The dielectric layer 20 can transmit excitation light.

  The dielectric layer 20 is formed by, for example, techniques such as vapor deposition, sputtering, CVD (Chemical Vapor Deposition), and various coatings. The dielectric layer 20 may be provided on the entire surface of the metal layer 10 or may be provided on a part of the surface of the metal layer 10.

The dielectric layer 20 only needs to have a positive dielectric constant. For example, silicon oxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), tantalum oxide (Ta ₂ O ₅ ), silicon nitride (Si ₃ N _4). ), Titanium oxide (TiO ₂ ), polymer such as PMMA (Polymethylmethacrylate), and ITO (Indium Tin Oxide). The dielectric layer 20 may be composed of a plurality of layers made of different materials. Specifically, the dielectric layer 20 may be a stacked body in which a silicon oxide layer is provided on an aluminum oxide layer. In this case, the aluminum oxide layer can function as an adhesion layer between the metal layer 10 and the silicon oxide layer.

  The thickness of the dielectric layer 20 is set so that the PSP excited at the interface between the metal layer 10 and the dielectric layer 20 can interact with the LSP excited by the metal particles 30. The thickness of the dielectric layer 20 is, for example, 10 nm to 1 μm, preferably 20 nm to 500 nm, and more preferably 30 nm to 100 nm.

1.3. Metal Particles The metal particles 30 are provided on the dielectric layer 20. In the illustrated example, the metal particles 30 are provided in contact with the dielectric layer 20. The shape of the metal particle 30 is not particularly limited. For example, the shape of the metal particle 30 is, for example, a cylinder, a prism, a sphere, a spheroid, an indefinite shape, or a combination thereof. In the illustrated example, the metal particle 30 has a cylindrical shape having a central axis in the thickness direction (Z-axis direction) of the dielectric layer 20.

  The thickness of the metal particle 30 is, for example, 1 nm to 100 nm, preferably 2 nm to 50 nm, more preferably 10 nm to 40 nm. The size of the metal particle 30 in the X-axis direction and the Y-axis direction (in the example shown, the diameter of the bottom surface of the cylinder) is 10 nm to 200 nm, preferably 30 nm to 180 nm, more preferably 80 nm to 150 nm. is there. The size of the metal particle 30 is smaller than the wavelength of incident light.

The material of the metal particles 30 is not particularly limited as long as the LSP can be excited by irradiation with excitation light, but is, for example, gold, silver, aluminum, copper, platinum, or an alloy thereof.

  The metal particles 30 can be formed by, for example, a patterning method after forming a thin film by sputtering, vapor deposition, or the like, a microcontact printing method, a nanoimprinting method, or the like. Alternatively, the metal particles 30 may be formed by a colloid chemical method.

  The metal particle 30 has a function of exciting the LSP in the sample analysis element 100. Specifically, by irradiating the metal particles 30 with excitation light, LSP can be excited in the metal particles 30 (around the metal particles 30).

  A plurality of metal particles 30 are provided. The plurality of metal particles 30 have a periodic arrangement that can excite PSP propagating through the interface between the metal layer 10 and the dielectric layer 20. In order to excite the PSP propagating through the interface between the metal layer 10 and the dielectric layer 20, the plurality of metal particles 30 are preferably arranged at a pitch about the wavelength of the excitation light in the polarization direction of the excitation light. . However, since the PSP dispersion curve changes depending on the material and thickness of the metal layer 10 and the dielectric layer 20, the plurality of metal particles 30 are not arranged at a pitch about the wavelength of the excitation light in the polarization direction of the excitation light. It may be possible.

  The arrangement of the plurality of metal particles 30 is not particularly limited as long as PSP propagating through the interface between the metal layer 10 and the dielectric layer 20 can be excited. In the illustrated example, the plurality of metal particles 30 are arranged in a matrix in the X-axis direction and the Y-axis direction. In other words, in the illustrated example, the plurality of metal particles 30 form a row in the X-axis direction, and the row is arranged in the Y-axis direction.

  The pitch in the X-axis direction of the plurality of metal particles 30 is not particularly limited as long as PSP propagating through the interface between the metal layer 10 and the dielectric layer 20 can be excited, and is 10 nm or more and 2 μm or less, preferably 20 nm. The thickness is 1 μm or more and more preferably 400 nm or more and 700 nm or less. The pitch in the X-axis direction is the distance between the centroids of adjacent metal particles 30 in the X-axis direction. If it does in this way, anti-crossing by the hybrid mode mentioned later can be raised and a target substance can be detected with high sensitivity.

  The pitch in the Y-axis direction of the plurality of metal particles 30 is not particularly limited as long as PSP propagating through the interface between the metal layer 10 and the dielectric layer 20 can be excited, and is 10 nm or more and 2 μm or less, preferably 20 nm. The thickness is 1 μm or more and more preferably 400 nm or more and 700 nm or less. Note that the pitch in the Y-axis direction is the distance between the centers of gravity of adjacent metal particles 30 in the Y-axis direction. The pitch in the X-axis direction of the plurality of metal particles 30 and the pitch in the Y-axis direction of the plurality of metal particles 30 may be different, but are the same in the illustrated example.

  The distribution, intensity, and the like of LSP excited by the metal particles 30 depend on the arrangement of the plurality of metal particles 30. Therefore, the LSP that electromagnetically interacts with the PSP excited by the metal layer 10 and the dielectric layer 20 considers not only the LSP excited by the single metal particle 30 but also the arrangement of the plurality of metal particles 30. In some cases, the LSP may be included.

Although not shown, an adhesion layer for improving the adhesion between the dielectric layer 20 and the metal particles 30 may be provided between the dielectric layer 20 and the metal particles 30. That is, the metal particle 30 may be provided on the dielectric layer 20 via the adhesion layer. Further, an adhesion layer for improving adhesion between the substrate 2 and the metal layer 10 may be provided between the substrate 2 and the metal layer 10. That is, the metal layer 10 may be provided on the substrate 2 through the adhesion layer. Thus, in this specification, for example, the expression “the member B is provided on the member A” refers to the case where the member B is provided in contact with the member A and the case where the member B is provided. And the case where the member B is provided via another member. The adhesion layer is, for example, a chromium layer or a titanium layer.

  The target substance 1 adheres (adsorbs) to the metal particles 30. The target substance 1 adheres to the metal particles 30 by bringing the sample analysis element 100 into contact with a gas sample containing the target substance 1. In the illustrated example, the target substance 1 is in contact with the metal particles 30 and the dielectric layer 20. The target substance 1 is a substance to be detected in the analysis using the sample analysis element 100. Examples of the target substance 1 include pyridine, acetic acid, acetone, methyl mercaptan, and toluene. For convenience, the target substance 1 is not shown in the example of FIG.

1.4. FIG. 3 shows the relationship between the arrangement of metal particles and the LSP (LSPR: Localized Surface).
It is a figure for demonstrating the relationship with Plasmon Resonance (PSPR) and PSP (PSPR: Propagating Surface Plasmon Resonance). In FIG. 3, (a) schematically shows the plane of the sample analysis element, (b) schematically shows the cross section along line BB of (a) of the sample analysis element, and (c ) Schematically shows a cross-sectional view taken along line CC of (a) of the sample analysis element.

  Here, the LSP generated around the metal particles (for example, the metal particles 30) includes a mode generated between adjacent metal particles (hereinafter referred to as “PPGM” (Particle-Particle Gap Mode)), and the metal particles. Two types of modes (hereinafter referred to as “PMGM” (Particle-Mirror Gap Mode)) occurring between metal layers (also having a mirror function) (for example, between metal particles 30 and metal layer 10). Is known to exist (see FIG. 3).

  Both of the two types of modes, PPGM and PMGM, are generated when excitation light is incident on the sample analysis element. Among these, PPGM LSP has higher strength as the metal particles approach (the distance between the metal particles is smaller). On the other hand, the LSP in the PMGM mode is not significantly affected by the arrangement of the metal particles and the polarization direction of the excitation light as in the PPGM LSP, and is irradiated between the metal particles and the metal layer (irradiation of the metal particles). (Down). As described above, the PSP is a plasmon that propagates through the interface between the metal layer and the light-transmitting layer. When the excitation light is incident on the metal layer, the interface between the metal layer and the light-transmitting layer is isotropic. Propagate to.

  FIG. 3 schematically shows a comparison between the hybrid structure used in the following experimental example and other structures (basic structure). The direction of polarization of the excitation light applied to the sample analysis element is indicated by an arrow in the figure. Note that the terms “basic structure” and “hybrid structure” are coined terms used to distinguish each of them in this specification, and their meanings will be described below.

  First, the basic structure is a structure in which metal particles are densely arranged on a light-transmitting layer, and the LSPR of PPGM and the LSPR of PMGM are excited by irradiation with excitation light. In this example, LSPR of PPGM is generated at both ends of the metal particles in the polarization direction of the excitation light. However, since the basic structure has a small anisotropy of the arrangement of the metal particles, the excitation light is not polarized light. Similarly, it is generated according to the electric field vector component of the excitation light. In the basic structure, as a result of the metal particles being densely arranged, the excitation light hardly reaches the metal layer, and therefore, little or no PSPR is generated. In the drawing, a schematic wavy line representing PSPR is omitted.

  The hybrid structure is a structure in which metal particles are arranged on a light-transmitting layer more sparsely than the basic structure, and the LSPR of PMGM is excited by irradiation with excitation light. In this example, the LSPR of PPGM is generated weakly as compared with the Basic structure because the metal particles are separated from each other, and is omitted in the drawing. In the hybrid structure, as a result of the metal particles being sparsely arranged, PSPR (dashed line in the figure) is generated.

  Note that FIG. 3 illustrates the case where polarized light is incident. However, in any structure, when non-polarized excitation light or circularly polarized light is incident, the component in the vibration direction of the electric field is included. In response, the SPR described above occurs.

  The overall SPR strength (electric field enhancement) in each structure is related to the sum (or product) of the SPRs generated in each. If the shape and size of the metal particles are the same in each structure, the contribution of PSPR to the strength of the total SPR increases in the order of Basic structure <Hybrid structure. In addition, the contribution of LSPR (PPGM and PMGM) to the strength of the total SPR is determined in the order of Hybrid structure <Basic structure from the viewpoint of metal particle density (HSD) when the shape and size of the metal particles are the same in each structure. It grows big. Further, when paying attention to LSPR of HSD and PPGM, the contribution degree of LSPR of PPGM to the strength of all SPRs increases in the order of Hybrid structure <Basic structure.

  The Hybrid structure has the strongest PSPR intensity and the largest contribution of the PSPR to the overall enhancement compared to the Basic structure. And although the intensity | strength of LSPR of PPGM is small and the density of a metal particle is also small, LSPR and PSPR of PMGM interact strongly electromagnetically (synergistic coupling | bonding).

  The Basic structure has the strongest strength of LSPR of PPGM, and the contribution of the LSPR of PPGM to the overall enhancement is the largest. And since the intensity | strength of PSPR is small, the electromagnetic interaction of LSPR of PPGM and PSPR does not generate | occur | produce. As shown in FIG. 6 to be described later, when metal particles are arranged densely, an absorption region due to PSPR does not occur. This can be seen from the fact that there is only one plot with an X-axis direction pitch of 300 nm as shown in FIG.

  Therefore, it can be said that the hybrid structure and the basic structure have different electric field enhancement mechanisms.

  In each structure, by changing the size of metal particles (for example, the diameter and thickness in plan view), the contribution of PSPR to the intensity of all SPR and the contribution of LSPR of PPGM to the intensity of all SPR Will change.

  The sample analysis element 100 according to the present embodiment has a hybrid structure, or a structure in which the period of the hybrid structure in the Y-axis direction is different. As shown in FIG. It has a periodic array that can excite PSP propagating through the interface with the dielectric layer 20. Then, the sample analysis element 100 is designed at the interface between the metal layer and the dielectric layer as shown in FIG. 3 by designing the thickness of the dielectric layer 20 so that the PSP and the LSP are electromagnetically coupled. The excited PSP and the LSP excited by the metal particles can be electromagnetically combined.

1.5. Resonance wavelength of propagation type surface plasmon and resonance wavelength of localized type surface plasmon In sample analysis element 100 concerning this embodiment, the resonance wavelength of propagation type surface plasmon (PSP) and the resonance wavelength of localization type surface plasmon (LSP) Is different. As shown in an experimental example to be described later, for example, the resonance wavelength of the LSP can be changed by changing the size (size in plan view) of the metal particles of the sample analysis element. Therefore, by changing the size of the metal particles 30 in plan view, the resonance wavelength of the PSP can be made longer than the resonance wavelength of the LSP or shorter than the resonance wavelength of the LSP in the sample analysis element 100. You can also. Hereinafter, the resonance wavelength of the PSP and the resonance wavelength of the LSP will be described in detail.

  First, propagation type surface plasmon (PSP) will be described. Normally, the dispersion relation of incident light (light line of n = 1) and the dispersion relation of PSP (dispersion relation of PSP propagating through the interface between Au and air) do not have an intersection, so that no PSP occurs. However, for example, when excited using incident light (diffracted light) that has passed through a diffraction grating having a grating interval Q, as shown in FIG. 4, the dispersion relation of PSP (the PSP propagating through the interface between Au and air) (Dispersion relationship) and the dispersion relationship (light line) of incident light (diffracted light) have an intersection, and the PSP at the wavelength of the intersection is excited. FIG. 4 is a diagram schematically showing a dispersion relation of surface plasmon polariton (SPP). Here, the SPP is a quantum of vibrations in which charge vibrations near the surface of the metal layer and electromagnetic waves are combined.

The wavelength at the intersection (see FIG. 4) is called the resonance wavelength of the PSP, and the resonance wavelength λ _PSP [nm] of the _PSP can be expressed by the following formula (1). The expression (1) shows the case where the excitation light (incident light) is perpendicularly incident (the case where the excitation light is incident in parallel to the vertical line on the upper surface of the dielectric layer).

λ _PSP (n = 1) <λ _PSP <λ _PSP (n ₂ ) (1)
here,
λ _PSP (n = 1) = [1240 × SQRT {ε ₁ (λ _in ) / (ε ₁ (λ _in ) +1)}] / (4π / X _p × 100) (2)
λ _PSP (n ₂ ) = [1240 × SQRT {ε ₁ (λ _in ) × ε ₂ / (ε ₁ (λ _in ) + ε ₂ )}] / (4π / X _p × 100) (3)

In Expressions (2) and (3), X _p [nm] is the pitch (period) of the metal particles in the polarization direction of the excitation light, and ε ₁ (ω) is the dielectric constant of the metal layer. Yes, ε ₂ (ε ₂ = n ₂ ² ) is the dielectric constant of the dielectric layer, and λ _in [nm] is the wavelength of the excitation light. Further, ω is an angular frequency of excitation light incident on the electric field enhancing element, and has a relationship of λ _in [nm] = 1240 / ω (eV).

The resonant wavelength of the PSP varies with the thickness of the dielectric layer. When the thickness of the dielectric layer having a dielectric constant ε ₂ is infinite, the PSP resonance wavelength is λ _PSP (n ₂ ). When the thickness of the dielectric layer is finite, the PSP resonance wavelength is expressed by the following equation (1): the resonance wavelength of PSP generated at the interface between the metal layer and air, the metal layer, and the dielectric layer having an infinite thickness. It takes a value between the resonance wavelength of PSP generated at the interface.

For example, in Experimental Example 1 described later, if the metal layer is an Au layer, the dielectric layer is a SiO ₂ layer (n ₂ = 1.46), X _p = 600 nm, and the wavelength λ _in is 630 nm, From the formula (1), 625 nm <λ _PSP <980 nm. From the result of FDTD (Finite Difference Time Domain) calculation, λ _PSP = 700 nm.

  Here, FIG. 5 is a diagram for explaining that the resonance wavelength of the PSP changes when the target substance adheres to the sample analysis element. As shown in FIG. 5, as the refractive index of the dielectric layer increases, the surface plasmon polariton (SPP) dispersion curve decreases and the energy of the SPP decreases at a certain wave number k. Therefore, the resonance wavelength of PSP becomes long.

  For example, as shown in FIG. 1, when the target substance 1 is adsorbed on the hot site (below the metal particles 30), the effective refractive index of the dielectric layer 20 in contact with the metal layer 10 increases, so the SPP dispersion curve decreases. , The resonance wavelength of the PSP becomes a long wavelength.

  Next, the resonance wavelength of LSP will be described. The LSP resonance wavelength (energy) of a metal sphere placed in a uniform surrounding medium is an energy ω that satisfies the following formula (4). Note that there is a relationship of λ = 1240 / ω.

ε ₁ (ω) = − 2ε ₀ (4)

In Equation (4), the dielectric constant of the metal is ε ₁ (ω), and the dielectric constant of the surrounding medium is ε ₀ .

  The resonance wavelength of LSP depends on the dielectric constant, shape, and surrounding dielectric constant of the metal particles. In the sample analysis element 100 according to the present embodiment, the interaction between the metal layer 10 and the metal particles 30 (PSP excited at the interface between the metal layer 10 and the dielectric layer 20, and the dielectric layer 20) Since there is an electromagnetic interaction with the LSP excited in the metal particle 30, the resonance wavelength of the LSP cannot be generally expressed by the equation (4).

  Therefore, as in an experimental example to be described later, the asymptotic line of the resonance wavelength of PSP and the asymptotic line of the resonance wavelength of LSP were obtained by changing the diameter of the metal particles (diameter in plan view). For example, the resonance wavelength of the PSP and the resonance wavelength of the LSP can be made different by designing the sample analysis element so as to avoid the diameter of the intersection of both asymptotes (the diameter of the metal particle). The asymptote of the resonance wavelength of the PSP and the asymptote of the resonance wavelength of the LSP can be obtained by changing parameters other than the diameter of the metal particle, and the value at the intersection of both asymptotes (the value of the changed parameter) By designing the sample analysis element so as to avoid (), the resonance wavelength of the PSP and the resonance wavelength of the LSP can be made different.

  In the sample analysis element 100 according to the present embodiment, an extremely large increase in electric field can be obtained by electromagnetically coupling a propagation surface plasmon (PSP) and a localized surface plasmon (LSP). it can.

FIG. 6 is a diagram for explaining anti-crossing by a hybrid, and shows a resonance wavelength when the pitch of the metal particles 30 in the X-axis direction is changed. The metal layer 10 is an Au layer, the dielectric layer 20 is a SiO ₂ layer, the thickness is 50 nm, the metal particles 30 are Au particles, the diameter is 100 nm, the height is 30 nm, the Y-axis direction pitch = the X-axis direction pitch, and FDTD The reflection spectrum was calculated by the (Finite Difference Time Domain) method to obtain the resonance wavelength.

The resonance wavelength of PSP in this structure (resonance wavelength of PSP propagating through the interface between the Au layer and the SiO ₂ layer) can be expressed by equation (1) and is predicted to be as shown by the broken line in FIG. The resonance wavelength of the LSP is a straight line substantially parallel to the horizontal axis.

  As shown in FIG. 6, when the resonance wavelength of the PSP approaches the resonance wavelength of the LSP, the absorption region caused by the LSP and the PSP splits (anti-crossing). In particular, when the wavelengths of LSP and PSP are equal, the effect of the hybrid mode is maximized.

  The sample analysis element according to the present invention uses points other than the point where the effect of the hybrid mode is maximized. That is, this is a case where the wavelengths of LSP and PSP are different.

  Since the dielectric constant of the surroundings changes when the substance is adsorbed (attached), the resonance wavelength of the LSP changes before and after the adsorption of the target substance. Thus, since the surrounding dielectric constant changes according to the adsorption amount and concentration of the target substance, the sample analysis element 100 can measure the adsorption amount and concentration of the target substance.

2. Analysis Method Next, an analysis method according to the present embodiment will be described with reference to the drawings. FIG. 7 is a flowchart for explaining the analysis method according to the present embodiment. FIG. 8 is a diagram for explaining the analysis method according to the present embodiment. 9 and 10 are diagrams for explaining a reflection spectrum acquired in the analysis method according to the present embodiment.

  The analysis method according to the present embodiment is a target substance analysis method using the sample analysis element according to the present invention. Below, the example using the sample analysis element 100 is demonstrated as a sample analysis element which concerns on this invention. 9 and 10 show an example in which the sample analysis element 100 in which the resonance wavelength of the PSP is longer than the resonance wavelength of the LSP.

  First, in a state where the target substance 1 is not attached to the sample analysis element 100, the sample analysis element 100 is irradiated with light, the reflected light from the sample analysis element 100 is detected, and the first reflection spectrum R1 is acquired ( S1).

  Specifically, as shown in FIG. 8, white light is emitted from the light source 110. The emitted white light reaches the sample analysis element 100 via the lens 3a, the half mirror 4, and the lens 3b, and is reflected by the sample analysis element 100. The light (reflected light) reflected by the sample analysis element 100 reaches the photodetector 120 via the lens 3b, the half mirror 4, and the lens 3c, and the photodetector 120 detects the reflected light. The photodetector 120 includes, for example, a spectroscope and a light receiving element, and the reflected light is received by the light receiving element via the spectroscope. The spectroscope is formed of, for example, an etalon using Fabry-Perot resonance. For example, a photodiode is used as the light receiving element. For example, a polarizer (not shown) may be disposed between the light source 110 and the lens 3a. For example, the reflectance spectra R1 and R2 shown in FIGS. 9 and 10 can be obtained by measuring the reflectance with a measurement system as shown in FIG. Note that the measurement system of the analysis method according to the present invention is not limited to the example shown in FIG.

As shown in FIG. 9, the first reflection spectrum R1 has a first absorption region P1 and a second absorption region P2 on the longer wavelength side than the first absorption region P1. The first absorption region P1 is an absorption region on the short wavelength side, and the second absorption region P2 is an absorption region on the long wavelength side. In the reflection spectrum, a drop in reflectivity indicates that SPR is occurring. When SPR is generated by irradiation with excitation light (incident light), absorption due to resonance occurs and the reflectance decreases. Therefore, the absorption region is a region where the reflectance of the reflection spectrum falls due to light absorption due to SPR resonance. The absorption region is, for example, a downward convex peak. As shown in FIG. 9, the reflection spectrum has two absorption regions (the first absorption region P1 and the second absorption region P2) because the PSP excited at the interface between the metal layer 10 and the dielectric layer 20, This is because the LSP excited by the metal particles 30 is electromagnetically combined and anti-crossing. That is, the first absorption region P1 and the second absorption region P2 are absorptions that are generated when the PSP and the LSP electromagnetically interact with each other. Similarly, a third absorption region P3 and a fourth absorption region P4, which will be described later, are absorptions that occur when PSP and LSP interact electromagnetically. As will be described later, the third absorption region P3 is a short wavelength side absorption region like the first absorption region P1, and the fourth absorption region P4 is a long wavelength side absorption region like the second absorption region P2. It is. Therefore, it can be said that the third absorption region P3 corresponds to the first absorption region P1, and the fourth absorption region P4 corresponds to the second absorption region P2. In the example shown in FIG. 9, the first absorption region P1 is an absorption region in which the contribution of LSP is larger than that of PSP, and the second absorption region P2
Is an absorption region where the contribution of PSP is greater than that of LSP. In the example shown in FIG. 9, the half width of the second absorption region P2 is smaller than the half width of the first absorption region P1.

  Here, the absorption region of the reflection spectrum according to the present invention will be described using the first absorption region P1. The absorption region of the reflection spectrum is a portion having a point (minimum point T1) at which the reflectance is minimized, and being lowered from the straight line L1 due to electromagnetic interaction between PSP and LSP. The straight line L1 is a local maximum point closest to the local minimum point T1 (a point where the reflectance is maximum) A from the local minimum point T1 to the short wavelength side, and a local maximum point closest to the local minimum point T1 from the local minimum point T1 to the long wavelength side. (Point where the reflectance is maximized) B. The difference between the reflectance at the minimum point T1 and the reflectance at the intersection C between the straight line L2 and the straight line L1 passing through the minimum point T1 and parallel to the vertical axis is, for example, 0.05 or more. When the local maximum point A is not present on the short wavelength side of the local minimum point T1, the straight line L1 is a maximum point (a point at which the reflectivity is maximum) A ′ on the short wavelength side of the local minimum point T1 and the local maximum point B. Is a line connecting When the local maximum point B is not present on the long wavelength side of the local minimum point T1, the straight line L1 has the local maximum point A and the maximum point on the long wavelength side of the local minimum point T1 (the point at which the reflectance becomes maximum) B '. Is a line connecting Further, when the local maximum points A and B are not provided, the straight line L1 is a line connecting the maximum point A ′ and the maximum store B ′. The same applies to the absorption regions P2, P3, and P4.

  Next, in a state where the target substance 1 is attached to the sample analysis element 100, the sample analysis element 100 is irradiated with light, the reflected light from the sample analysis element 100 is detected, and the second reflection spectrum R2 is acquired. (S2).

  Specifically, a gas sample containing the target substance 1 is brought into contact with the sample analysis element 100, and the target substance 1 is attached (adsorbed) to the metal particles 30 of the sample analysis element 100. Then, similarly to the step (S1), a white light source is emitted from the light source 110, and the reflected light reflected by the sample analysis element 100 is detected by the photodetector 120. Thereby, 2nd reflection spectrum R2 shown in FIG. 10 is acquirable. In FIG. 10, the first reflection spectrum R1 is also illustrated, and the first reflection spectrum R1 is indicated by a solid line and the second reflection spectrum R2 is indicated by a broken line.

  The second reflection spectrum R2 has a third absorption region P3 corresponding to the first absorption region P1 and a fourth absorption region P4 corresponding to the second absorption region P2. At least one of the third absorption region P3 and the fourth absorption region P4 is obtained by shifting the first absorption region P1 or the second absorption region P2 to the long wavelength side. In the example shown in FIG. 10, the second reflection spectrum R2 corresponds to the first absorption region P1, and corresponds to the third absorption region P3 and the second absorption region P2 in which the first absorption region P1 is shifted to the long wavelength side. The second absorption region P2 has a fourth absorption region P4 shifted to the long wavelength side. For example, the third absorption region P3 is an absorption region in which the first absorption region P1 is shifted to the long wavelength side due to the target substance 1 adhering to the sample analysis element 100, and the fourth absorption region P4 The second absorption region P2 is an absorption region shifted to the long wavelength side by adhering to the sample analysis element 100. The third absorption region P3 is an absorption region on the short wavelength side, and the fourth absorption region P4 is an absorption region on the long wavelength side. In the example illustrated in FIG. 10, the third absorption region P3 is an absorption region where the contribution of LSP is greater than that of PSP, and the fourth absorption region P4 is an absorption region where the contribution of PSP is greater than that of LSP. In the example shown in FIG. 10, the half width of the fourth absorption region P4 is smaller than the half width of the third absorption region P3.

  Note that if the third absorption region P3 is shifted to the longer wavelength side than the first absorption region P1, the fourth absorption region P4 may not be shifted with respect to the second absorption region P2. That is, the difference between the wavelength of the minimum point of the second absorption region P2 and the wavelength of the minimum point of the fourth absorption region P4 may be zero. Further, if the fourth absorption region P4 is shifted to the longer wavelength side than the second absorption region P2, the third absorption region P3 may not be shifted with respect to the first absorption region P1. That is, the difference between the wavelength of the minimum point of the first absorption region P1 and the wavelength of the minimum point of the third absorption region P3 may be zero.

  Next, the difference Δλ1 between the wavelength of the minimum point T1 of the first absorption region P1 and the wavelength of the minimum point T3 of the third absorption region P3, the wavelength of the minimum point T2 of the second absorption region P2, and the fourth absorption region P4 A difference Δλ2 from the wavelength of the minimum point T4 is calculated (S3).

  Next, the target substance 1 is detected using the absorption region having the larger difference between the differences Δλ1 and Δλ2 calculated in the step (S3) (S4). The larger difference between the differences Δλ1 and Δλ2 is, for example, 1 nm or more, preferably 4 nm or more.

  In the example shown in FIG. 10, the resonance wavelength of PSP is longer than the resonance wavelength of LSP, and in step (S4), the target substance 1 is detected using the first absorption region P1 and the third absorption region P3. In the sample analysis element 100 in which the resonance wavelength of PSP is longer than the resonance wavelength of LSP, the difference Δλ1 is larger than the difference Δλ2, as shown in FIG. Thus, by detecting the target substance 1 and collating the difference Δλ1 with a previously obtained calibration curve, the adsorption amount and concentration of the target substance can be obtained.

  In the above example, the target substance analysis method using the sample analysis element in which the resonance wavelength of the PSP is longer than the resonance wavelength of the LSP has been described. Next, a method for analyzing a target substance using a sample analysis element in which the resonance wavelength of PSP is shorter than the resonance wavelength of LSP will be described. In the following, differences from the target substance analysis method using the sample analysis element in which the resonance wavelength of the PSP is longer than the resonance wavelength of the LSP will be described, and description of similar points will be omitted.

  FIG. 11 is a diagram for explaining a reflection spectrum acquired in the sample analysis element 100 in which the resonance wavelength of the PSP is shorter than the resonance wavelength of the LSP. In FIG. 11, the first reflection spectrum R1 is indicated by a solid line, and the second reflection spectrum R2 is indicated by a broken line.

  In the example shown in FIG. 11, the first absorption region P1 of the first reflection spectrum R1 is an absorption region where the contribution of PSP is larger than that of LSP, and the second absorption region P2 of the first reflection spectrum R1 is more than PSP. This is an absorption region where the contribution of LSP is large. In the example shown in FIG. 11, the half width of the first absorption region P1 is smaller than the half width of the second absorption region P2.

  In the example shown in FIG. 11, the third absorption region P3 of the second reflection spectrum R2 is an absorption region where the contribution of PSP is larger than that of LSP, and the fourth absorption region P4 of the second reflection spectrum R2 is more than PSP. This is an absorption region where the contribution of LSP is large. In the example shown in FIG. 11, the half width of the third absorption region P3 is smaller than the half width of the fourth absorption region P4.

  In the example shown in FIG. 11, the resonance wavelength of PSP is shorter than the resonance wavelength of LSP, and in step (S4), target substance 1 is analyzed using second absorption region P2 and fourth absorption region P4. In the sample analysis element 100 in which the resonance wavelength of the PSP is shorter than the resonance wavelength of the LSP, as shown in FIG. 11, the difference Δλ2 is larger than the difference Δλ1.

  The analysis method according to the present embodiment has the following features, for example.

In the analysis method according to the present embodiment, the difference Δλ1 between the wavelength of the minimum point T1 of the first absorption region P1 and the wavelength of the minimum point T3 of the third absorption region P3, and the wavelength of the minimum point T2 of the second absorption region P2 The target substance 1 is detected using the step of calculating the difference Δ2 with respect to the wavelength of the minimum point T4 of the fourth absorption region P4 and the absorption region having the larger difference between the calculated differences Δλ1 and Δλ2. In the sample analysis element 100 used in the present embodiment, the PSP propagating through the interface between the metal layer 10 and the dielectric layer 20 and the LSP excited by the metal particles 30 are electromagnetically coupled to each other. In effect, the resonance wavelength of the PSP and the resonance wavelength of the LSP are different. Therefore, in the analysis method according to the present embodiment, when the sample analysis element having the same resonance wavelength of the PSP and the resonance wavelength of the LSP is used, the wavelength of the minimum point of the absorption region of the reflection spectrum before and after attachment of the target substance is measured. One of the differences Δλ1 and Δλ2 can be made larger than the difference (change amount) Δλ (see FIG. 10). In the analysis method according to the present embodiment, at least one of the first absorption region P1 and the second absorption region P2, and at least one of the third absorption region P3 and the fourth absorption region P4 are the resonance wavelength of the PSP and the resonance wavelength of the LSP. LSP contributes more than the absorption region of the reflection spectrum when the same sample analysis element is used, and one of the differences Δλ1 and Δλ2 can be made larger than Δλ (see FIG. 10). As described above, the analysis method according to the present embodiment can increase the wavelength change amount of the minimum value of the absorption region of the reflection spectrum before and after the adhesion of the target substance, and uses an absorption region having a large wavelength change amount. Since the target substance 1 can be detected, the target substance 1 can be detected with high sensitivity.

  For example, if the concentration of the target substance is small, the wavelength of the minimum point in the absorption region of the reflection spectrum hardly changes before and after the target substance is attached, and it may be difficult to detect the target substance. However, since the analysis method according to the present embodiment can detect the target substance 1 using the absorption region where the amount of wavelength change is large as described above, even the target substance 1 having a low concentration can be detected. The concentration of the target substance 1 is, for example, 1 ppb or more and 1% or less.

  FIG. 12 illustrates a reflection spectrum before the target substance is attached and a reflection spectrum after the target substance is attached when a sample analysis element having the same PSP resonance wavelength and LSP resonance wavelength is used. FIG. In FIG. 12, the reflection spectrum before the target substance is attached is indicated by a solid line, and the reflection spectrum after the target substance is attached is indicated by a broken line.

3. Experimental Example An experimental example is shown below to describe the present invention more specifically. The present invention is not limited by the following experimental examples.

3.1. Experimental example 1
3.1.1. Model In Experimental Example 1, a far solution (reflection spectrum) was obtained by FDTD (Finite Difference Time Domain) simulation. FIG. 13 is a diagram for explaining the model M1 used in Experimental Example 1. As shown in FIG. 13, an Au layer is used as a metal layer, a SiO ₂ layer is provided as a dielectric layer on the Au layer, and cylindrical Au particles are provided as metal particles on the SiO ₂ layer to obtain a model M1. .

In the model M1, the thickness of the Au layer was 150 nm. The thickness of the SiO ₂ layer was 50 nm, and the refractive index of the SiO ₂ layer was 1.46. The diameter of the Au particles in plan view (hereinafter also simply referred to as “diameter”) was changed in the range of 80 nm to 150 nm, and the thickness of the Au particles was set to 30 nm. The Au particles were provided in a matrix in the X-axis direction and the Y-axis direction, and the pitch of the Au particles in the X-axis direction and the Y-axis direction was 600 nm. The Lorenz Drude model was used for the refractive index of Au. The incident light was linearly polarized light in the X-axis direction, and the light was incident vertically on the upper surface of the SiO ₂ layer. The refractive index n ₀ around the model M1 was set to 1.

  For the calculation, FDTD soft FullWAVE of Rsoft (currently Cybernet System Co., Ltd.) was used. The conditions for simulation of the reflection spectrum are a minimum mesh of 2 nm and a calculation time of 32 μm.

3.1.2. Calculation of reflection spectrum The reflection spectrum was calculated by changing the diameter of Au particles in the range of 80 nm to 150 nm. Two absorption regions (decrease in reflectivity) appeared in the reflection spectrum. FIG. 14 is a graph plotting the wavelengths of the minimum points (minimum points of reflectance) of two absorption regions in the reflection spectrum when the diameter of the Au particles is changed in the range of 80 nm to 150 nm.

As shown in FIG. 14, plots each asymptotic to two straight lines were obtained. A straight line having a constant wavelength even when the diameter of the Au particle changes indicates the resonance wavelength of the PSP. A straight line whose wavelength changes as the diameter of the Au particle changes indicates the resonance wavelength of the LSP. The diameter of the intersection IP of the straight line L _PSP indicating the resonance wavelength of the _PSP and the straight line _LLSP indicating the resonance wavelength of the _LSP is the wavelength of the minimum point of the absorption region on the short wavelength side and the wavelength of the minimum point of the absorption region on the long wavelength side It is the diameter when the difference between is the smallest. Therefore, in FIG. 14, a straight line asymptotic to the plot is drawn so that the diameter of the intersection point IP is 104 nm. When the resonance wavelength of the PSP and the resonance wavelength of the LSP approach each other, the PSP and the LSP are combined (hybrid), and the absorption region caused by the PSP and the LSP splits (anti-crossing) away from the straight line L _PSP and the straight line L _LSP. . When the resonance wavelength of the PSP is equal to the resonance wavelength of the LSP (at the intersection IP), the effect of the hybrid mode is maximized and the anti-crossing is maximized.

When the LSP and the PSP are not coupled (when they are not electromagnetically interacting), the absorption region of the LSP (the drop in the reflection spectrum based on the LSP absorption) is broad (the half-value width is large), and the PSP The absorption region (drop of reflection spectrum based on PSP absorption) is sharp (the half width is small). In FIG. 14, the absorption region that is asymptotic to the straight line L _LSP (the absorption region where the plot of the minimum point is asymptotic) is derived from the LSP (the contribution of the LSP is greater than the PSP). Therefore, when the resonance wavelength of the PSP is larger than the resonance wavelength of the LSP, the absorption region appearing on the short wavelength side becomes broad, and when the resonance wavelength of the PSP is smaller than the resonance wavelength of the LSP, the absorption appearing on the long wavelength side. The area becomes broad. Furthermore, in the absorption region that is asymptotic to the straight line L _LSP (an absorption region where the contribution of PSP is larger than that of LSP), as shown in Experimental Example 2, the amount of change in the wavelength of the minimum point of the absorption region before and after the target substance attachment is large. In the analysis method according to the present invention, the target substance is detected using an absorption region where the contribution of LSP is larger than that of PSP. In FIG. 14, a region including a plot corresponding to an absorption region in which the contribution of LSP is larger than that of PSP is indicated by hatching.

3.2. Experimental example 2
3.2.1. Model In Experimental Example 2, the far solution (reflection spectrum) was obtained by FDTD (Finite Difference Time Domain) simulation. In Experimental Example 2, the model M1 used in Experimental Example 1 and the model M2 shown in FIGS. 15 and 16 were used.

As shown in FIGS. 15 and 16, the model M2 is the same as the model M1 except that a dielectric is provided in contact with the Au particles and the SiO ₂ layer. The dielectric of the model M2 has a cylindrical shape, a diameter of 20 nm, a height of 10 nm, a refractive index of 1.1, and a surrounding refractive index of 1. The dielectric of the model M2 corresponds to the target substance. The reflection spectrum in the model M1 used in the experimental example 2 corresponds to the reflection spectrum in a state before the target substance adheres to the sample analysis element, and the reflection spectrum in the model M2 used in the experimental example 2 has the target substance in the sample analysis element. It corresponds to the reflection spectrum of the state after being attached. In Experimental Example 2, the diameter of the metal particles was changed to 80 nm, 104 nm, and 130 nm. Except for these, in Experimental Example 2, the reflection spectrum was calculated under the same conditions as in Experimental Example 1.

  15 and 16 are diagrams for explaining the model M2. FIG. 15 is a cross-sectional view taken along the line XV-XV of FIG. 16 schematically showing the model M2. FIG. It is a top view which shows typically.

3.2.2. Calculation of reflection spectrum FIG. 17 shows a reflection spectrum when the diameter of the Au particles is 80 nm. FIG. 18 shows Au
It is a reflection spectrum when the diameter of the particles is 104 nm. FIG. 19 is a reflection spectrum when the diameter of the Au particles is 130 nm. 17 to 19, the reflection spectrum in the model M1 (the reflection spectrum before the target substance adheres to the sample analysis element) is shown by a solid line, and the reflection spectrum in the model M2 (after the target substance has adhered to the sample analysis element) The reflection spectrum in this state is indicated by a broken line.

  As shown in FIGS. 17 to 19, in the sample analysis element having a Au particle diameter of 80 nm or 130 nm (a sample analysis element in which the resonance wavelength of PSP is different from the resonance wavelength of LSP), the sample analysis in which the diameter of Au particle is 104 nm It was found that a larger wavelength shift can be obtained before and after deposition of the target substance than the device (sample analysis device in which the resonance wavelength of PSP and the resonance wavelength of LSP are equal).

  In the sample analysis element in which the diameter of the Au particle is 80 nm, the resonance wavelength of the PSP is longer than the resonance wavelength of the LSP (see FIG. 14), so the absorption region on the short wavelength side has a larger contribution of the LSP than the PSP. As shown in FIG. 17, the wavelength shift is larger before and after the target substance is adhered than in the absorption region on the long wavelength side. Therefore, in the 80 nm sample analysis element, the target substance can be detected with high sensitivity using the absorption region on the short wavelength side.

  As shown in FIG. 18, the sample analysis element having a Au particle diameter of 104 nm has almost no wavelength shift before and after the target substance is attached.

  In the sample analysis element in which the diameter of the Au particle is 130 nm, the resonance wavelength of the PSP is shorter than the resonance wavelength of the LSP (see FIG. 14), so the absorption region on the long wavelength side contributes more to the PSP than the LSP. As shown in FIG. 19, the wavelength shift is larger before and after the target substance is attached than the absorption region on the short wavelength side. Therefore, the target substance can be detected with high sensitivity using the absorption region on the long wavelength side.

  As shown in FIG. 17 and FIG. 19, the sample analysis element with a diameter of 130 nm has a larger drop in reflectance than the sample analysis element with a diameter of 80 nm nm, and the absorption region can be easily recognized.

  Since the change in the wavelength of the LSP occurs due to a change in the dielectric constant around the Au particles, the absorption region where the contribution of the LSP is large is greatly shifted (the shift amount is large) when the amount of the target substance to be attached is very small. When the amount of adsorption is large (when the refractive index around the sample analysis element is high), the absorption region where the contribution of PSP is large is also shifted.

3.3. Experimental example 3
3.3.1. Sample analysis element A sample analysis element was prepared and the reflectance was measured. A glass substrate was used as a substrate, a Cr layer as an adhesion layer was formed on the substrate by a sputtering method, and an Au layer was formed as a metal layer on the Cr layer by a sputtering method. The thickness of the Cr layer was 5 nm or less, and the thickness of the Au layer was 100 nm. Next, an Al ₂ O ₃ layer and an SiO ₂ layer were formed as a dielectric layer on the Au layer in this order by sputtering. The thickness of the Al ₂ O ₃ layer was 5 nm or less, and the thickness of the SiO ₂ layer was 50 nm.

Next, Au particles were formed as metal particles on the SiO ₂ layer. Specifically, a resist is applied on the SiO ₂ layer, a circular pattern (pattern part) is patterned by EBL (Electron Beam Lithography), and then an Au layer is formed by a vacuum deposition method. The Au layer was lifted off to form Au particles. The Au particles were formed in a matrix in the X-axis direction and the Y-axis direction, and the pitch of the Au particles in the X-axis direction and the Y-axis direction was 600 nm. The thickness of the Au particles was 30 nm.

In this experimental example, a plurality of Au particles having different diameters were formed. Specifically, Au particles having a diameter of 117 nm were formed in a matrix in the first region on the SiO ₂ layer, and Au particles having a diameter of 129 nm were formed in a matrix in the second region on the SiO ₂ layer. The size of each region in plan view is 100 μm × 100 μm.

3.3.2. Reflectance measurement After the sample analysis element formed as described above was sufficiently exposed to a pyridine saturated gas, the reflectance was measured by irradiating a white light source. The polarization direction of incident light was the X-axis direction.

  FIG. 20 is a reflection spectrum in a region where the diameter of Au particles is 117 nm. FIG. 21 is a reflection spectrum in a region where the diameter of Au particles is 129 nm.

  As shown in FIG. 20 and FIG. 21, three depressions (downward convex peaks) appeared in the wavelength range of 550 nm to 850 nm. Of the three depressions, the central depression D is caused by the measurement system (specifically, the objective lens of the measurement system), so the noted depression is the two depressions on both sides (short wavelength side). Absorption region on the long wavelength side).

  In the region where the diameter of the Au particle shown in FIG. 20 is 117 nm, the wavelength difference between the minimum points of the absorption region on the short wavelength side before and after the adsorption of the target substance is 2.31 nm. The wavelength difference between the minimum points in the absorption region was 0.96 nm. In the region where the diameter of the Au particles is 117 nm, the target substance is detected using the absorption region on the short wavelength side.

  In the region where the diameter of the Au particles shown in FIG. 21 is 129 nm, the wavelength difference between the minimum points of the absorption region on the short wavelength side before and after the adsorption of the target substance is 4.28 nm. The wavelength difference at the minimum point of the absorption region was 4.66 nm. In the region where the diameter of the Au particles is 129 nm, the target substance is detected using the absorption region on the long wavelength side.

  The above-described embodiments and modifications are merely examples, and the present invention is not limited to these. For example, it is possible to appropriately combine each embodiment and each modification.

  The present invention includes configurations that are substantially the same as the configurations described in the embodiments (for example, configurations that have the same functions, methods, and results, or configurations that have the same objects and effects). In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that exhibits the same operational effects as the configuration described in the embodiment or a configuration that can achieve the same object. Further, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

DESCRIPTION OF SYMBOLS 1 ... Target substance, 2 ... Substrate, 3a, 3b, 3c ... Lens, 4 ... Half mirror, 10 ... Metal layer, 20 ... Dielectric layer, 30 ... Metal particle, 100 ... Sample analysis element, 110 ... Light source, 120 ... Detector

Claims (3)

A method for analyzing a target substance using a sample analysis element,
In a state where the target substance is not attached to the sample analysis element, the sample analysis element is irradiated with light to detect reflected light from the sample analysis element, and a first absorption region and the first absorption region Obtaining a first reflection spectrum having a second absorption region on the longer wavelength side,
In a state where the target substance is attached to the sample analysis element, the sample analysis element is irradiated with light, reflected light from the sample analysis element is detected, and a third absorption corresponding to the first absorption region is detected. And a fourth absorption region corresponding to the second absorption region, and at least one of the third absorption region and the fourth absorption region is long in the first absorption region or the second absorption region. Obtaining a second reflection spectrum that is shifted to the wavelength side;
The difference between the wavelength of the minimum point of the first absorption region and the wavelength of the minimum point of the third absorption region, and the difference between the wavelength of the minimum point of the second absorption region and the wavelength of the minimum point of the fourth absorption region And a step of calculating
Detecting the target substance using an absorption region having a larger difference among the calculated differences;
Including
The sample analysis element is:
A metal layer,
A dielectric layer provided on the metal layer;
A plurality of metal particles provided on the dielectric layer;
Have
The plurality of metal particles have a periodic array capable of exciting propagating surface plasmons propagating through an interface between the metal layer and the dielectric layer,
The propagation type surface plasmon and the localized type surface plasmon excited by the metal particle interact electromagnetically,
An analysis method in which a resonance wavelength of the propagation surface plasmon is different from a resonance wavelength of the localized surface plasmon. In claim 1,
The propagation wavelength of the propagation surface plasmon is longer than the resonance wavelength of the localized surface plasmon,
In the step of detecting the target substance,
An analysis method, wherein the target substance is analyzed using the first absorption region and the third absorption region. In claim 1,
The propagation wavelength of the propagation surface plasmon is shorter than the resonance wavelength of the localized surface plasmon,
In the step of detecting the target substance,
An analysis method of analyzing the target substance using the second absorption region and the fourth absorption region.

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