JP2022055689A - Raman spectroscopy measuring device, raman spectroscopy measuring method and surface enhanced raman scattering device - Google Patents

Abstract

To provide a surface enhanced Raman scattering device which shows surface enhanced Raman scattering intensity with high intensity and uniform distribution to some extent.SOLUTION: A surface enhanced Raman scattering device 100 includes a light reflecting layer 120, a dielectric layer 130 disposed on the light reflecting layer 120, and a plurality of metallic nanostructures 140 disposed on the dielectric layer.SELECTED DRAWING: Figure 1

Description

The present invention relates to a Raman spectroscopic measuring device, a Raman spectroscopic measuring method and a surface-enhanced Raman scattering device.

In recent years, surface-enhanced Raman scattering spectroscopy using surface plasmon resonance (SPR), especially Localized Surface Plasmon Resonance (LSPR), is one of the techniques for measuring molecules under test with high sensitivity. Is attracting attention. Surface-Enhanced Raman Scattering (SERS) is a phenomenon in which when a molecule is adsorbed on the surface of a metal having a nanometer-scale uneven structure, the intensity of Raman scattered light emitted from the molecule increases significantly. Is. In surface-enhanced Raman spectroscopy (SERS), the Raman scattered light emitted from the measured molecule is irradiated with excitation light of a single wavelength such as laser light on the measured molecule adsorbed on the surface of the metal. Is spectrally detected to obtain a Raman spectrum. The molecule to be measured can be identified from this Raman spectrum.

As the surface-enhanced Raman scattering device used for surface-enhanced Raman scattering spectroscopy, a chip in which a plurality of metal nanostructures are arranged on a substrate is used. As such a surface-enhanced Raman scattering device, a chip in which a metal nanostructure having a characteristic shape is arranged on a substrate is disclosed with a focus on enhancing a local electric field in nanospace in order to increase sensitivity. (For example, Patent Document 1, Non-Patent Document 1 and Non-Patent Document 2).

International Publication No. 2006/073117

Christopher G. Khoury and Tuan Vo-Dinh, "Gold Nanostars For Surface-Enhanced Raman Scattering: Synthesis, characterization and Optimization", J. Phys. Chem. C, Vol. 112, No. 48, pp. 18849-18859. Adam D. McFarland, Matthew A. Young, Jon A. Dieringer, and Richard P. Van Duyne, "Wavelength-scanned surface-enhanced Raman excitation spectroscopy", J. Phys. Chem. B, Vol. 109, No. 22, pp. 11279-11285.

In the above-mentioned conventional surface-enhanced Raman scattering device, a structure for increasing the intensity of the nanometer-scale enhanced electric field (hot spot) is adopted for high sensitivity, but the structure is limited to several tens of nm. Only a part of the space that has been created becomes a hotspot. Therefore, the spatial distribution of hot spots is not uniform but scattered and non-uniform. Therefore, when the concentration of the molecule to be measured in the sample is low, the probability that the molecule to be measured is adsorbed on the hot spot is reduced, so that there is a problem that the quantitativeness and reproducibility of the measurement result are low. On the other hand, in order to solve this problem, if the distribution of the electric field enhancement in the surface-enhanced Raman scattering device is made uniform, the electric field enhancement becomes smaller, so that the detection sensitivity of the measurement result is lowered. Occurs.

From the above, a surface-enhanced Raman scattering device that exhibits high intensity and spatially uniform surface-enhanced Raman scattering intensity to some extent and is capable of performing Raman spectroscopic measurement with high quantitativeness and reproducibility is desired.

Therefore, an object of the present invention is to provide a surface-enhanced Raman scattering device exhibiting a surface-enhanced Raman scattering intensity having high intensity and a uniform distribution to some extent. It is also an object of the present invention to provide a Raman spectroscopic measuring device and a Raman spectroscopic measuring method using the surface-enhanced Raman scattering device.

The Raman spectroscopic measuring apparatus according to the present invention includes a surface-enhanced Raman scattering device, a light source that irradiates the surface-enhanced Raman scattering device with excitation light, and a spectroscope that disperses Raman-scattered light from the surface-enhanced Raman scattering device. The surface-enhanced Raman scattering device includes a detector for detecting Raman scattered light dispersed by the spectroscope, a light reflecting layer, a dielectric layer arranged on the light reflecting layer, and the dielectric. It has a plurality of metal nanostructures arranged on the body layer.

The Raman spectroscopic measurement method according to the present invention includes a step of irradiating a surface-enhanced Raman scattering device with excitation light and detecting Raman scattered light from the surface-enhanced Raman scattering device, and the surface-enhanced Raman scattering device is light. It has a reflective layer, a dielectric layer arranged on the light reflecting layer, and a plurality of metal nanostructures arranged on the dielectric layer.

The surface-enhanced Raman scattering device according to the present invention has a light reflecting layer, a dielectric layer arranged on the light reflecting layer, and a plurality of metal nanostructures arranged on the dielectric layer.

According to the present invention, it is possible to provide a surface-enhanced Raman scattering device exhibiting a surface-enhanced Raman scattering intensity having high intensity and a uniform distribution to some extent. Further, according to the present invention, Raman spectroscopic measurement with high quantitativeness and reproducibility can be performed.

FIG. 1 is a schematic cross-sectional view showing an example of the configuration of the surface-enhanced Raman scattering device according to the present invention. FIG. 2 is a graph showing the relationship between the thickness of the gold thin film and the Q value. 3A to 3C are schematic cross-sectional views showing an example of a method for manufacturing a surface-enhanced Raman scattering device according to the present invention. FIG. 4 is a schematic diagram showing the configuration of the Raman spectroscopic measuring device according to the present invention. FIG. 5 is a scanning electron microscope image showing the state of the surface of the surface-enhanced Raman scattering device produced in Experiment 1. 6A and 6B are graphs showing the absorption spectra of the surface-enhanced Raman scattering device prepared in Experiment 1. 7A to 7C are diagrams showing the intensity distribution of Raman scattered light in Experiment 1, and FIGS. 7D to 7F are graphs showing the intensity distribution of Raman scattered light in Experiment 1. 8A and 8B are diagrams showing the intensity distribution of Raman scattered light in Experiment 1, and FIGS. 8C and 8D are graphs showing the intensity distribution of Raman scattered light in Experiment 1. 9A and 9B are schematic cross-sectional views showing the configuration of the surface-enhanced Raman scattering device produced in Experiment 2. FIG. 10 is a graph showing the relationship between the embedding depth of gold nanoparticles and the Raman spectrum.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Surface-enhanced Raman scattering device)
FIG. 1 is a schematic cross-sectional view showing the configuration of a surface-enhanced Raman scattering device 100 according to an embodiment of the present invention. As shown in FIG. 1, the surface-enhanced Raman scattering device 100 has a support substrate 110, a light reflecting layer 120, a dielectric layer 130, and a plurality of metal nanostructures 140. Hereinafter, each component will be described.

The support substrate 110 supports the light reflecting layer 120 and the dielectric layer 130. The support substrate 110 is not an essential component from the viewpoint of the function of the surface-enhanced Raman scattering device 100, but from the viewpoint of maintaining the structure of the surface-enhanced Raman scattering device 100, the surface-enhanced Raman scattering device 100 is the support substrate 110. It is preferable to have. The material and shape of the support substrate 110 are not particularly limited. From the viewpoint of maintaining the structure of the surface-enhanced Raman scattering device 100, the support substrate 110 preferably has a certain degree of mechanical strength. Examples of the support substrate 110 include a glass plate, a ceramic plate, a metal plate, and a resin plate.

The light reflection layer 120 is arranged on the support substrate 110 and reflects the excitation light. The configuration of the light reflecting layer 120 is not particularly limited as long as it can exhibit the above functions, and may be appropriately selected depending on the wavelength of the excitation light. For example, the light reflecting layer 120 is a layer made of metal (metal thin film), a dielectric multilayer film, or the like. Further, the metal plate may be provided with the functions of both the light reflecting layer 120 and the support substrate 110. When the light reflecting layer 120 is made of metal, the type of metal is not particularly limited. Examples of metals constituting the light reflecting layer 120 include gold, silver, copper, titanium and aluminum. The thickness of the light reflecting layer 120 is not particularly limited as long as it can exhibit the above function, and is, for example, in the range of 10 to 10,000 nm. When the metal plate has the functions of both the light reflecting layer 120 and the support substrate 110, the metal plate (light reflecting layer 120) naturally has a thickness of 10,000 nm or more.

The dielectric layer 130 is a layer (dielectric thin film) made of a dielectric arranged on the light reflecting layer 120. As will be described later, in the surface-enhanced Raman scattering device 100 according to the present embodiment, the light reflection layer 120 and the dielectric layer 130 function as Fabry-Perot resonators when irradiated with excitation light. Therefore, it is preferable that the front surface and the back surface of the dielectric layer 130 are parallel to each other. The type of dielectric constituting the dielectric layer 130 is not particularly limited as long as it can function as a Fabry-Perot resonator. From the viewpoint of functioning as a Fabry-Perot resonator, it is preferable that the dielectric has a high refractive index. Specifically, the refractive index at the resonance wavelength of the Fabry-Perot resonator is preferably 1.4 or more, and more preferably 2.0 or more for more efficient light confinement. Examples of the dielectric constituting the dielectric layer 130 include titanium oxide, strontium titanate, gallium nitride, zirconium oxide and nickel oxide. The thickness of the dielectric layer 130 is also not particularly limited as long as it can function as a Fabry-Perot resonator when irradiated with excitation light. For example, the thickness of the dielectric layer 130 is about 20 to 1000 nm. By adjusting the thickness of the dielectric layer 130, the resonance wavelength of the Fabry-Perot resonator can be changed. In the surface-enhanced Raman scattering device 100 according to the present embodiment, the thickness of the dielectric layer 130 may be 20 nm or more, 50 nm or more, or 100 nm or more.

From the viewpoint of improving the detection sensitivity, the light reflection layer 120 and the dielectric layer 130 may be configured so that the Q value (Quality factor, co-promotion frequency f ₀ / full width at half maximum Δf) of the Fabry-Perot resonator is large. preferable. For example, FIG. 2 is a graph showing the relationship between the thickness of the gold thin film (light reflecting layer 120) and the Q value. From this result, it can be seen that the thickness of the gold thin film (light reflecting layer 120) is preferably large to some extent (for example, 40 nm or more) from the viewpoint of increasing the Q value. It is considered that this is because if the gold thin film (light reflecting layer 120) is too thin, the excitation light is partially transmitted. From the viewpoint of increasing the Q value, it is preferable that the interface between the light reflecting layer 120 and the dielectric layer 130 and the interface between the dielectric layer 130 and the outside are smooth. That is, it is preferable that the roughness of the front surface and the back surface of the dielectric layer 130 is small. Further, it is preferable that the difference in refractive index between the media is large. That is, it is preferable that the refractive index of the dielectric constituting the dielectric layer 130 is high. Further, it is preferable that the absorption of the excitation light by the dielectric layer 130 is small.

The plurality of metal nanostructures 140 generate localized surface plasmon resonance when irradiated with excitation light. The plurality of metal nanostructures 140 may be arranged on the surface of the dielectric layer 130 so that a part thereof is embedded in the dielectric layer 130, but from the viewpoint of increasing the surface-enhanced Raman scattering intensity, the dielectric is dielectric. It is preferably arranged on the dielectric layer 130 so as not to be substantially buried in the body layer 130 (see FIG. 10). This is because when the metal nanostructure 140 is partially buried in the dielectric layer 130, the hot spots existing in the lower part of the metal nanostructure 140 are buried in the dielectric layer 130, which has the effect of enhancing the electric field. It is thought that this is because it is reduced. Here, "substantially not buried in the dielectric layer 130" means a portion of the metal nanostructure 140 located on the light reflecting layer 120 side of the surface of the dielectric layer 130 around it (dielectric layer). It means that the ratio of the portion (the part buried in 130) is 10% or less. The ratio of the portion buried in the dielectric layer 130 is preferably 5% or less, more preferably 3% or less, and particularly preferably 0%. When the proportion of the portion buried in the dielectric layer 130 is 0%, the entire metal nanostructure 140 exists on the surface of the dielectric layer 130. The surface of each metal nanostructure 140 that is not in contact with the dielectric layer 130 is exposed to the outside. Molecules to be measured are adsorbed on this surface.

The shape, size and spacing of the metal nanostructures 140 are not particularly limited as long as they can generate localized surface plasmon resonance when irradiated with light. By adjusting the shape, size or spacing of the metal nanostructures 140, the resonance wavelength of the localized surface plasmon resonance can be changed from the visible region to the near infrared region. Therefore, the shape, size and spacing of the metal nanostructures 140 can be appropriately selected so that localized surface plasmon resonance occurs at the wavelength of the excitation light. For example, the shape of the metal nanostructure 140 includes a substantially spherical shape, a substantially spherical crown shape (including a substantially hemispherical shape), a rod shape, a disc shape, and a cone shape. The maximum length of the metal nanostructure 140 is about 5 to 1000 nm. The spacing between the metal nanostructures 140 is about 3 to 1000 nm. As described above, a part of the surface of the plurality of metal nanostructures 140 is exposed to the outside.

As described above, in the surface-enhanced Raman scattering device 100 according to the present embodiment, the plurality of metal nanostructures 140 generate localized surface plasmon resonance when irradiated with excitation light, and the light reflecting layer 120 and the light reflecting layer 120 and the light reflecting layer 120. The dielectric layer 130 functions as a Fabry-Perot resonator when irradiated with excitation light. Further, the surface-enhanced Raman scattering device 100 according to the present embodiment is configured such that the resonance wavelength of the Fabry-Perot resonator is within the range of the peak wavelength of the localized surface plasmon resonance ± the half width of the peak. .. In this way, when the resonance wavelength of the Fabry-Perot resonator is within the range of the peak wavelength of the localized surface plasmon resonance ± the half-value width of the peak, a strong coupling is formed between the localized surface plasmon and the Fabry-Perot resonator. As a result, a large number of hot spots can be formed on the surface of the surface-enhanced Raman scattering device 100 with a somewhat uniform distribution. From the viewpoint of increasing the degree of strong coupling, it is preferable that the resonance wavelength of the localized surface plasmon resonance and the resonance wavelength of the Fabry-Perot resonator match.

When a strong or super-strong bond occurs between the localized surface plasmon and the Fabry-Perot resonator as described above, the plasmon of each metal nanostructure 140 has a quantum coherent interaction via the Fabry-Perot resonator. Is induced, and it is considered that the plasmon oscillation spreads to all the metal nanostructures 140 and the phases are aligned. In order to maximize the interaction and make the electric field enhancement distribution uniform, it is preferable that the metal nanostructures 140 are present in the vicinity. Specifically, the occupancy rate (coverage rate) of the metal nanostructure 140 on the surface of the surface-enhanced Raman scattering device 100 (the surface of the region where the plurality of metal nanostructures 140 are arranged) is 20% or more. It is preferably, more preferably 35% or more, and even more preferably 50% or more.

The method for manufacturing the surface-enhanced Raman scattering device 100 according to the present embodiment is not particularly limited. For example, the surface-enhanced Raman scattering device 100 can be manufactured by the following procedure (see FIGS. 3A to 3C).

First, a metal layer as the light reflecting layer 120 is prepared (FIG. 3A). In the example shown in FIG. 3A, a metal layer as a light reflecting layer 120 is formed on the support substrate 110. The method for forming the metal layer is not particularly limited. Examples of metal layer forming methods include sputtering, vacuum deposition, electrical reduction and ion plating. Further, a metal plate may be prepared as the light reflecting layer 120 (and the support substrate 110).

Next, the dielectric layer 130 is formed on the surface of the metal layer (light reflecting layer 120) (FIG. 3B). The method for forming the dielectric layer 130 is not particularly limited. Examples of methods for forming the dielectric layer 130 include atomic layer deposition, pulsed laser deposition, sputtering, solvothermal, spray pyrolysis and molecular beam epitaxy. When the dielectric layer 130 is formed by the atomic layer deposition method, it is preferable to perform a pretreatment in order to form the dielectric layer 130 densely on the surface of the metal layer (light reflecting layer 120). Examples of the pretreatment include a surface treatment for adding a hydroxyl group to the surface of the metal layer (light reflecting layer 120) and a treatment for forming another layer (for example, a titanium thin film) on the surface of the metal layer (light reflecting layer 120). Is included. For example, a compound having a functional group containing S or N (for example, a thiol group) at one end and a hydroxyl group at the other end (for example, 2-mercaptoethanol) as a binding site to the metal layer (light reflecting layer 120). ) May be used for surface treatment. Further, when a titanium thin film is formed on the surface of the metal layer (light reflecting layer 120), the titanium thin film is naturally oxidized in the atmosphere, and a hydroxyl group is generated on the surface of the titanium thin film.

Finally, a plurality of metal nanostructures 140 are formed on the dielectric layer 130 (FIG. 3C). The method for forming the metal nanostructure 140 is not particularly limited. For example, by forming a metal layer on the dielectric layer 130 and then annealing the metal layer into particles, a plurality of substantially spherical crown-shaped metal nanostructures 140 can be formed at the same time. Further, a plurality of metal nanostructures 140 may be formed by using photolithography.

By the above procedure, the surface-enhanced Raman scattering device 100 can be manufactured.

(Raman spectroscopic measuring device and Raman spectroscopic measuring method)
FIG. 4 is a schematic diagram showing the configuration of the Raman spectroscopic measuring device 200 according to the embodiment of the present invention. As shown in FIG. 4, the Raman spectroscopic measuring device 200 includes the surface-enhanced Raman scattering device 100, a light source 220, an optical system 230, a spectroscope 240, and a detector 250. In the present embodiment, the Raman spectroscopic measuring device 200 has a device holder 210, and the surface-enhanced Raman scattering device 100 is installed in the device holder 210. Hereinafter, each component will be described.

The device holder 210 supports the surface-enhanced Raman scattering device 100 in a predetermined position. The configuration of the device holder 210 is not particularly limited. The device holder 210 may be a stage for mounting the surface-enhanced Raman scattering device 100, or may have a structure for holding the surface-enhanced Raman scattering device 100.

The light source 220 irradiates the surface-enhanced Raman scattering device 100 with excitation light 260. From the viewpoint of appropriately measuring the Raman shift, the excitation light 260 is preferably light having substantially a single wavelength. The wavelength of the excitation light 260 is not particularly limited and may be appropriately set according to the type of the molecule to be measured and the like. Further, from the viewpoint of increasing the intensity of Raman scattered light, the excitation light 260 is preferably light having high intensity. For example, laser light is used as the excitation light 260. The type of the light source 220 is not particularly limited as long as it can emit the excitation light 260 having a desired wavelength and intensity, and is, for example, a laser diode.

The optical system 230 guides the excitation light 260 emitted from the light source 220 to the surface-enhanced Raman scattering device 100, and guides the Raman scattered light 270 from the surface-enhanced Raman scattering device 100 to the spectroscope 240. The configuration of the optical system 230 is not particularly limited as long as the above functions can be realized. FIG. 4 shows a beam splitter 231 that transmits the excitation light 260 and reflects the Raman scattered light 270, and a lens (condensing lens) 232, but the configuration of the optical system 230 is not limited to this. For example, the optical system 230 may further include various filters such as an excitation light cut filter for removing Rayleigh scattered light, and various lenses such as a collimator lens.

The spectroscope 240 disperses Raman scattered light 270 from the surface-enhanced Raman scattering device 100. In order to obtain information on the molecule to be measured from the Raman scattered light 270, it is necessary to decompose the Raman scattered light 270 for each wave number. Therefore, the spectroscope 240 disperses the Raman scattered light 270. The configuration of the spectroscope 240 is not particularly limited. For example, the spectroscope 240 is a polychromator that includes a diffraction grating.

The detector 250 detects the Raman scattered light 270 dispersed by the spectroscope 240. The type of the detector 250 is not particularly limited as long as it can appropriately detect weak Raman scattered light, and can be appropriately selected according to the wavelength (wavenumber) range to be detected. For example, the detector is a cooled CCD.

As the Raman spectroscopic measuring device 200, a known Raman spectroscopic measuring device can be used for components other than the surface-enhanced Raman scattering device 100.

Next, Raman spectroscopic measurement (Raman spectroscopic measurement method according to an embodiment of the present invention) using the Raman spectroscopic measuring device 200 will be described.

First, a liquid sample containing a molecule to be measured is provided in a region where a plurality of metal nanostructures 140 of the surface-enhanced Raman scattering device 100 are arranged. Some of the molecules under test in the liquid sample are adsorbed on the metal nanostructures 140 of the surface-enhanced Raman scattering device 100. After this, the liquid sample is dried to remove the solvent. The surface-enhanced Raman scattering device 100 after drying is installed in the device holder 210.

Next, the surface-enhanced Raman scattering device 100 is irradiated with excitation light 260 from the light source 220. As a result, surface-enhanced Raman scattering occurs at the interface between the surface of the plurality of metal nanostructures 140 and the molecule to be measured, and the Raman scattered light derived from the molecule to be measured is enhanced and emitted up to, for example, ¹⁰⁸ times. As described above, in the surface-enhanced Raman scattering device 100 according to the present embodiment, the plurality of metal nanostructures 140 generate localized surface plasmon resonance when irradiated with excitation light, and the light reflecting layer 120 and the light reflecting layer 120 and the light reflecting layer 120. The dielectric layer 130 functions as a Fabry-Perot resonator when irradiated with excitation light. As a result, a large number of hot spots are formed with a somewhat uniform distribution on the surface of the surface-enhanced Raman scattering device 100. Therefore, high-intensity Raman scattered light is emitted from the region where the plurality of metal nanostructures 140 of the surface-enhanced Raman scattering device 100 are arranged, with the intensity distribution being uniform to some extent.

Then, the Raman scattered light emitted from the surface-enhanced Raman scattering device 100 is separated by the spectroscope 240, and the separated Raman scattered light is detected by the detector 250. A Raman spectrum can be obtained from the detection result of the detector 250. From this Raman spectrum, for example, the molecule to be measured can be identified.

By the above procedure, the molecule to be measured in the liquid sample can be analyzed.

In the above description, an example of drying a liquid sample on the surface-enhanced Raman scattering device 100 has been described, but it is of course possible to perform Raman spectroscopic measurement without drying the liquid sample. At this time, in order to prevent the concentration change due to the volatilization of the solvent, it is preferable to seal and measure the liquid sample provided on the surface-enhanced Raman scattering device 100.

(effect)
As described above, in the surface-enhanced Raman scattering device 100 according to the present embodiment, a large number of hot spots are generated by combining the electric field enhancing effect by the localized surface plasmon resonance and the light confinement effect by the Fabry-Perot resonator. It is realized that the distribution is uniform to some extent. Therefore, high-intensity Raman scattered light is emitted from the region where the plurality of metal nanostructures 140 of the surface-enhanced Raman scattering device 100 according to the present embodiment are arranged, with the intensity distribution being uniform to some extent. .. Therefore, the surface-enhanced Raman scattering device, the Raman spectroscopic measurement device, and the Raman spectroscopic measurement method according to the present embodiment can perform Raman spectroscopic measurement with high quantitativeness and reproducibility.

Further, in the surface-enhanced Raman scattering device 100 according to the present embodiment, when visible light is irradiated, an oxidation reaction proceeds on the surface of the device. Therefore, the surface-enhanced Raman scattering device 100 according to the present embodiment can be reused by oxidatively decomposing and removing the molecule to be measured and the like.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples.

[Experiment 1]
1. 1. Fabrication of Surface-enhanced Raman Scattering Device A gold thin film (light reflection layer) with a thickness of 100 nm was formed on a glass plate as a support substrate by sputtering. A titanium thin film having a thickness of 2 nm was formed by sputtering on the glass plate on which the gold thin film was formed. The titanium thin film naturally oxidizes in the atmosphere, and hydroxyl groups are generated on the surface of the titanium thin film. A titanium oxide (TiO ₂ ) thin film (dielectric layer) having a film thickness of 30 nm was formed on the titanium thin film using an atomic layer deposition apparatus. A gold thin film having a thickness of 3 nm is formed on the titanium oxide thin film by vacuum deposition and annealed at 300 ° C. for 2 hours to atomize the gold thin film into particles, and a plurality of substantially spherical crown-shaped gold nanoparticles (metal nanostructures). Formed. The average particle size of the gold nanoparticles was 16 nm. Virtually all gold nanoparticles were placed on the titanium oxide thin film without being partially embedded in the titanium oxide thin film. FIG. 5 is a scanning electron microscope image showing the state of the surface on which the gold nanoparticles of the prepared surface-enhanced Raman scattering device are arranged. By the above procedure, the surface-enhanced Raman scattering device according to the example was produced.

For comparison, the surface-enhanced Raman scattering device according to the comparative example was produced by the same procedure as above except that a gold thin film (light reflecting layer) was not formed. For comparison, a SERS substrate (J12853) manufactured by Hamamatsu Photonics Co., Ltd. and an Au nanorod array substrate (Wavelet) for SERS measurement by Nidec Co., Ltd. were prepared as commercially available surface-enhanced Raman scattering devices.

FIG. 6A is a graph showing the absorption spectrum of the surface-enhanced Raman scattering device according to the embodiment, and FIG. 6B shows the absorption spectrum of the surface-enhanced Raman scattering device according to the comparative example having no gold thin film (light reflecting layer). It is a graph which shows. The vertical axis is the absorption spectrum value (actual scale) calculated from the transmission spectrum value (T) and the reflection spectrum value (R). Further, in FIG. 5A, the wavelength of the excitation light used in the subsequent evaluation is shown by a broken line at 532 nm.

In the surface-enhanced Raman scattering device according to the above embodiment, 1/4 n (n) of a Fabry-Perot resonator composed of a gold thin film, a titanium oxide thin film and gold nanoparticles has a plasmon resonance wavelength of 650 nm of gold nanoparticles. The resonance wavelengths corresponding to the refractive index of titanium oxide) match. This means that the resonance wavelength of the Fabry-Perot cavity and the localized surface plasmon resonance wavelength of the gold nanoparticles overlap, and the phases of the two oscillators exchange energy with a constant relationship due to electromagnetic field interaction. It means that the state of being is formed. As a result, two new energy levels, bonding and antibonding, are generated, so that the absorption spectrum is bimodal, and its response range and intensity are greatly increased.

2. 2. Evaluation of Surface-enhanced Raman Scattering Devices For each surface-enhanced Raman scattering device, the surface-enhanced Raman scattering spectrum was measured using a microscopic Raman measuring device (see FIG. 4). The surface-enhanced Raman scattering device was immersed in a 1 μM crystal violet aqueous solution and then dried. After that, using a micro-Raman measuring device, excitation light with a wavelength of 532 nm (laser power: ~ 300 μW, irradiation time: 0.5 seconds) is focused and irradiated to the region where a plurality of metal nanostructures are arranged. A surface-enhanced Raman scattering spectrum of crystal violet molecules was obtained. Regardless of which surface-enhanced Raman scattering device was used, large peaks due to crystal violet molecules were observed at 1617 cm ^-1 and 1371 cm ^-1 in the Raman spectrum (see FIG. 10).

7A to 7C are diagrams showing the intensity distribution of Raman scattered light for 1617 cm ^-1 , and FIGS. 7D to 7F are graphs showing the intensity distribution of Raman scattered light for 1617 cm ^-1 . 7A and 7D show the results of the surface-enhanced Raman scattering device according to the embodiment, FIGS. 7B and 7E show the results of the commercially available surface-enhanced Raman scattering device (J12853), and FIGS. 7C and 7F are shown. The results of a commercially available surface-enhanced Raman scattering device (Wavelet) are shown. In FIGS. 7A to 7C, the intensity distribution in the range of 20 μm × 20 μm is shown in gray scale. In FIGS. 7D to 7, this range is divided into 625 sections, and the intensities of each section are plotted. In addition, FIGS. 7D to 7F also show the mean value (Mean), standard deviation (Standard Deviation), and coefficient of variation (CV) (%) of the intensity.

First, looking at the average value (Mean) of the intensity of each device, it can be seen that the device according to the embodiment can detect Raman scattered light caused by crystal violet molecules with a sensitivity equal to or higher than that of a commercially available device. Understand. Looking at the coefficient of variation (CV) of the intensity of each device, the device according to the embodiment has a uniform intensity distribution (the coefficient of variation is 1/5 or less) as compared with the commercially available device. Understand. From these facts, the device according to the example has a sensitivity equal to or higher than that of a commercially available device, and has high quantitativeness and reproducibility even when the concentration of the molecule to be measured in the sample is low. It turns out that can be measured.

8A and 8B are diagrams showing the intensity distribution of Raman scattered light for 1617 cm- ¹ , and FIGS. 8 and 8D are graphs showing the intensity distribution of Raman scattered light for 1617 cm ^-1 . 8A and 8C show the results of the surface-enhanced Raman scattering device according to the embodiment (same data as FIGS. 7A and 7D), and FIGS. 8B and 8D are comparatives without a gold thin film (light reflecting layer). The results of the surface-enhanced Raman scattering device according to the example are shown. In FIGS. 8A and 8B, the intensity distribution in the range of 20 μm × 20 μm is shown in gray scale. In FIGS. 8C and 8D, this range is divided into 625 compartments and the intensities of each compartment are plotted. In addition, FIGS. 8C and 8D also show the mean value (Mean), standard deviation (Standard Deviation) and coefficient of variation (CV) (%) of the intensity. It should be noted that the digits of the numerical values on the vertical axis are different between FIGS. 8C and 8D.

From FIGS. 8B and 8D, the device according to the comparative example having no gold thin film (light reflecting layer) uses only the electric field enhancing effect due to the localized surface plasmon resonance, and therefore cannot sufficiently enhance Raman scattered light. It can be seen (average value of intensity: 13.6). On the other hand, from FIGS. 8A and 8C, the device according to the embodiment having the gold thin film (light reflecting layer) has not only the electric field enhancing effect by the localized surface plasmon resonance but also the light confinement effect by the Fabry-Perot resonator. It can be seen that the Raman scattered light can be sufficiently enhanced because it is used (average intensity: 189). It can also be seen that by utilizing the optical confinement effect of the Fabry-Perot resonator, the intensity distribution becomes uniform (the coefficient of variation becomes 1/3 or less).

[Experiment 2]
1. 1. Fabrication of Surface-enhanced Raman Scattering Device A gold thin film (light reflecting layer) with a thickness of 100 nm was formed on a glass plate as a support substrate by sputtering. A titanium thin film having a thickness of 2 nm was formed by sputtering on the glass plate on which the gold thin film was formed. The titanium thin film naturally oxidizes in the atmosphere, and hydroxyl groups are generated on the surface of the titanium thin film. A titanium oxide (TiO ₂ ) thin film (dielectric layer) having a film thickness of 30 nm was formed on the titanium thin film using an atomic layer deposition apparatus. A gold thin film having a thickness of 3 nm is formed on the titanium oxide thin film by vacuum deposition and annealed at 300 ° C. for 2 hours to atomize the gold thin film into particles, and a plurality of substantially spherical crown-shaped gold nanoparticles (metal nanostructures). Formed. The average particle size of the gold nanoparticles was 16 nm. After that, a titanium oxide thin film (dielectric layer) having a predetermined thickness was formed again using an atomic layer deposition apparatus. At this time, by forming the titanium oxide thin film on the surface of the gold nanoparticles without performing the surface treatment for modifying the hydroxyl group, the plurality of gold nanoparticles are formed without forming the titanium oxide thin film on the plurality of gold nanoparticles. A titanium oxide thin film having a predetermined thickness was formed between the particles. As a result, substantially all the gold nanoparticles were partially buried in the titanium oxide thin film (partially exposed to the outside).

FIG. 9A shows the configuration of the surface-enhanced Raman scattering device when the titanium oxide thin film is not formed after the gold nanoparticles (metal nanostructure 140) are formed on the titanium oxide thin film (dielectric layer 130). It is a schematic diagram which shows. In this device, the depth of the embedded portion of the gold nanoparticles (metal nanostructures 140) is 0 nm.

FIG. 9B shows a surface-enhanced Raman in the case where gold nanoparticles (metal nanostructures 140) are formed on a titanium oxide thin film (dielectric layer 130a) and then a titanium oxide thin film (dielectric layer 130b) is further formed. It is a schematic diagram which shows the structure of a scattering device. In this experiment, the thickness of the above titanium oxide thin film (dielectric layer 130b) was set to 3 nm, 5 nm, 7 nm or 9 nm. Therefore, in this device, the depth of the embedded portion of the gold nanoparticles (metal nanostructures 140) is 3 nm, 5 nm, 7 nm or 9 nm. Even when the thickness of the titanium oxide thin film (dielectric layer 130b) was 9 nm, the upper part of the gold nanoparticles (metal nanostructure 140) was exposed to the outside.

2. 2. Evaluation of Surface-enhanced Raman Scattering Devices For each surface-enhanced Raman scattering device, the surface-enhanced Raman scattering spectrum was measured using a microscopic Raman measuring device (see FIG. 4). The surface-enhanced Raman scattering device was immersed in a 1 μM crystal violet aqueous solution and then dried. After that, using a micro-Raman measuring device, excitation light with a wavelength of 532 nm (laser power: 3.08 mW, irradiation time: 2 seconds) is focused and irradiated to the region where multiple metal nanostructures are arranged, and the crystal is crystallized. A surface-enhanced Raman scattering spectrum of violet molecules was obtained.

FIG. 10 is a graph showing the relationship between the embedding depth of gold nanoparticles and the Raman spectrum. From top to bottom, the spectrum of the device with an embedding depth of 0 nm (Inlaid 0 nm), the spectrum of the device with an embedding depth of 3 nm (Inlaid 3 nm), and the spectrum of the device with an embedding depth of 5 nm (Inlaid 5). Shows the spectrum of a device with an embedding depth of 7 nm (Inlaid 7 nm), the spectrum of a device with an embedding depth of 9 nm (Inlaid 9 nm), and the spectrum of a device with an embedding depth of 11 nm (Inlaid 11 nm). There is.

From this graph, it can be seen that as the embedding depth of the gold nanoparticles decreases, the peak intensity indicating the Raman shift increases. This is because when the metal nanoparticles are partially buried in the titanium oxide thin film, the strengthening field (hot spot) existing at the bottom of the metal nanoparticles is buried in the titanium oxide thin film, and the effect of electric field strengthening is reduced. It is thought that this is because it ends up. From this result, it can be seen that it is preferable not to embed the gold nanoparticles in the titanium oxide thin film in order to increase the strength of the electric field and increase the measurement sensitivity.

The surface-enhanced Raman scattering device, the Raman spectroscopic measurement device, and the Raman spectroscopic measurement method according to the present invention are useful for, for example, various analyzes because they can perform Raman spectroscopic measurement with high quantitativeness and reproducibility.

100 Surface-enhanced Raman Scattering Device 110 Support Substrate 120 Light Reflection Layer 130 Dielectric Layer 140 Metal Nanostructure 200 Raman Spectrometer 210 Device Holder 220 Light Source 230 Optical System 231 Beam Splitter 232 Lens 240 Spectrometer 250 Detector 260 Excitation Light 270 Raman scattered light

Claims (12)

Surface-enhanced Raman scattering device and
A light source that irradiates the surface-enhanced Raman scattering device with excitation light,
A spectroscope that disperses Raman scattered light from the surface-enhanced Raman scattering device, and
A detector that detects Raman scattered light dispersed by the spectroscope, and a detector.
Have,
The surface-enhanced Raman scattering device is
Light reflective layer and
The dielectric layer arranged on the light reflecting layer and
A plurality of metal nanostructures arranged on the dielectric layer, and
Have,
Raman spectroscopy measuring device. The plurality of metal nanostructures generate localized surface plasmon resonance when irradiated with the excitation light.
The light reflecting layer and the dielectric layer function as Fabry-Perot resonators when irradiated with the excitation light.
The Raman spectroscopic measuring apparatus according to claim 1. The Raman spectroscopic measuring apparatus according to claim 2, wherein the resonance wavelength of the Fabry-Perot resonator is within the range of the peak wavelength of the localized surface plasmon resonance ± the half width of the peak. The Raman spectroscopic measuring apparatus according to any one of claims 1 to 3, wherein the plurality of metal nanostructures are arranged on the dielectric layer so as not to be substantially embedded in the dielectric layer. It has a step of irradiating a surface-enhanced Raman scattering device with excitation light and detecting Raman scattered light from the surface-enhanced Raman scattering device.
The surface-enhanced Raman scattering device is
Light reflective layer and
The dielectric layer arranged on the light reflecting layer and
A plurality of metal nanostructures arranged on the dielectric layer, and
Have,
Raman spectroscopy measurement method. The plurality of metal nanostructures generate localized surface plasmon resonance when irradiated with the excitation light.
The light reflecting layer and the dielectric layer function as Fabry-Perot resonators when irradiated with the excitation light.
The Raman spectroscopic measurement method according to claim 5. The Raman spectroscopic measurement method according to claim 6, wherein the resonance wavelength of the Fabry-Perot resonator is within the range of the peak wavelength of the localized surface plasmon resonance ± the half width of the peak. The Raman spectroscopic measurement method according to any one of claims 5 to 7, wherein the plurality of metal nanostructures are arranged on the dielectric layer so as not to be substantially embedded in the dielectric layer. Light reflective layer and
The dielectric layer arranged on the light reflecting layer and
A plurality of metal nanostructures arranged on the dielectric layer, and
A surface-enhanced Raman scattering device with. The plurality of metal nanostructures generate localized surface plasmon resonance when irradiated with excitation light.
The light reflecting layer and the dielectric layer function as Fabry-Perot resonators when irradiated with the excitation light.
The surface-enhanced Raman scattering device according to claim 9. The surface-enhanced Raman scattering device according to claim 10, wherein the resonance wavelength of the Fabry-Perot resonator is within the range of the peak wavelength of the localized surface plasmon resonance ± the half width of the peak. The surface-enhanced Raman scattering device according to any one of claims 9 to 11, wherein the plurality of metal nanostructures are arranged on the dielectric layer so as not to be substantially embedded in the dielectric layer. ..

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