Method for producing substrate with metal nanoparticle layer

Abstract

To provide a method for producing a low-cost SERS substrate having a metal nanoparticle layer strongly attached to the substrate.SOLUTION: A method for producing a substrate with a metal nanoparticle layer comprises a thin film formation step of forming, on a substrate, a thin film by making a solution containing a metal salt, a water-soluble polymer, and a catalyst into a thin film by a spin-coating method, and a reduction step of reducing the metal salt in the thin film obtained through the thin film formation step. The metal salt preferably includes at least one selected from the group consisting of silver nitrate and gold chloride. The water-soluble polymer preferably includes polyvinyl alcohol. The catalyst preferably includes platinum. The substrate is preferably a substrate used for surface-enhanced Raman scattering.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a substrate provided with a metal nanoparticle layer. [Background technology]

[0002] Surface-enhanced Raman scattering (SERS) is a method for easily detecting substances by amplifying weak Raman scattered light (which provides specific information about the substance) by a factor of 103 to 106. SERS is applicable to a wide range of fields because it can detect trace amounts of substances (at the single-molecule level) quickly and with high sensitivity. A SERS substrate with a metal nanoparticle layer is used in the SERS method.

[0003] Non-Patent Document 1 discloses a method for manufacturing a SERS substrate by electron beam lithography, Non-Patent Document 2 discloses a method for manufacturing a SERS substrate by metal vapor deposition, and Non-Patent Document 3 discloses a method for manufacturing a SERS substrate by wet chemical synthesis. Expensive equipment, advanced operating techniques, and a vacuum environment are required in the electron beam lithography and metal vapor deposition methods, and the SERS substrates manufactured by these methods are very expensive, even though most are disposable.

[0004] The solutions used in wet chemical synthesis are difficult to handle, and the metal nanoparticles in the solution tend to aggregate, making uniform dispersion difficult and resulting in poor adhesion to the substrate. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Hatab et al., ACS Nano 2 (2008), 377 [Non-patent document 2] Hulteen et al., J. Phys. Chem. B 103 (1999), 3854 [Non-patent document 3] Dzhagan et al., J. Nanopart. Res. 25 (2023), 37 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, there has been a demand for a method for producing an inexpensive SERS substrate in which a metal nanoparticle layer is firmly attached to the substrate.

[0007] Therefore, the problem to be solved by the present invention is to provide a method for producing an inexpensive SERS substrate in which a metal nanoparticle layer is firmly attached to the substrate. [Means for solving the problem]

[0008] The present inventors have conducted extensive research in light of the above-mentioned problems and have found that a method for manufacturing a SERS substrate, which involves spin-coating an aqueous solution containing a metal salt, a water-soluble polymer, and a catalyst into a thin film on a substrate and then reducing the metal salt in the thin film, provides a method for manufacturing an inexpensive SERS substrate in which a metal nanoparticle layer is firmly attached to the substrate.The present invention was completed based on these findings.

[0009] The present invention relates to a method for manufacturing a substrate having a metal nanoparticle layer, the method including a thin film formation step of forming a thin film on a substrate by spin coating a solution containing a metal salt, a water-soluble polymer, and a catalyst, and a reduction step of reducing the metal salt in the thin film obtained through the thin film formation step. The metal salt preferably includes at least one selected from the group consisting of silver nitrate and gold chloride. The water-soluble polymer preferably includes polyvinyl alcohol. The catalyst preferably comprises platinum. The substrate is preferably a substrate used in surface-enhanced Raman scattering. [Effects of the Invention]

[0010] The method of the present invention for producing a substrate with a metal nanoparticle layer provides an inexpensive SERS substrate in which the metal nanoparticle layer is firmly attached to the substrate. [Brief explanation of the drawings]

[0011] [Figure 1] Field emission scanning electron microscope images of silver nanoparticle layers on three different substrates. [Figure 2] FIG. 1 shows the relationship between the surface free energy of three types of substrates and the average particle size and interparticle distance (nanogap) of silver nanoparticles. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will now be described in further detail. Unless otherwise specified, the symbol "to" in a numerical range indicates a range from above to below, and both ends of the range are included. Furthermore, when a numerical range is indicated, the upper and lower limits can be combined as appropriate, and the resulting numerical range is also considered to be disclosed.

[0013] The method for producing a substrate having a metal nanoparticle layer of the present invention includes a thin film formation step of forming a thin film on a substrate by spin coating a solution containing a metal salt, a water-soluble polymer, and a catalyst. Examples of the metal salt include silver nitrate, gold chloride, and silver borate. The metal salt preferably includes at least one selected from the group consisting of silver nitrate and gold chloride, and more preferably at least one selected from the group consisting of silver nitrate and gold chloride. The content of the metal salt in the solvent is preferably in the range of 5 to 50% by mass.

[0014] Examples of the water-soluble polymer include synthetic polymers such as polyvinyl alcohol, polyacrylic acid, polyacrylamide, polyethylene oxide, polyvinylamide, and polyamine, and natural polymers such as protein and starch. The water-soluble polymer preferably includes polyvinyl alcohol, and more preferably is polyvinyl alcohol. The content of the water-soluble polymer in the solvent is preferably in the range of 5 to 20% by mass.

[0015] Examples of the catalyst include platinum, palladium, and rhodium. The catalyst preferably contains platinum, and more preferably is platinum. The content of the catalyst in the solvent is preferably in the range of 0.005 to 0.1% by mass.

[0016] Examples of the solvent for the solution include water, dimethylformamide, and ethanol. The solvent preferably contains water, and more preferably is water.

[0017] Examples of materials constituting the substrate include glass, metal, resin, silicon, and sapphire. The substrate is preferably a disk-shaped glass substrate. When the dispersion component of the surface free energy of the substrate increases, the particle diameter of the metal nanoparticles constituting the metal nanoparticle layer on the substrate tends to increase, and the nanogap tends to decrease. Therefore, the microstructure of the metal nanoparticle layer is controlled by the material of the substrate. The surface free energy of the substrate is preferably 40 to 80 (mJ / m 2 ), the dispersion component is preferably 20 to 50 (mJ / m 2 ) range.

[0018] When the solution is dropped onto a disk-shaped substrate that is rotating at high speed, the solution is converted into a thin film. As a result, a thin film is formed on the substrate. The rotation speed of the substrate is preferably in the range of 3000 to 9000 rpm. The mass of the solution dropped onto 1 cm2 of the substrate is preferably in the range of 0.02 to 2 g.

[0019] The method for manufacturing a substrate having a metal nanoparticle layer of the present invention includes a reduction step of reducing the metal salt in the thin film obtained through the thin film formation step. For example, the substrate on which the thin film has been formed is placed on a heating unit such as a heated ceramic heater, and the thin film and the substrate are heated in the atmosphere. The metal salt in the thin film is reduced, and a metal nanoparticle layer is formed on the substrate. The temperature of the heated substrate is preferably in the range of 200 to 300°C, and the heating time is preferably in the range of 5 to 60 minutes.

[0020] The average particle size of the metal nanoparticles constituting the metal nanoparticle layer is preferably in the range of 1 to 100 nm, more preferably in the range of 5 to 50 nm, and even more preferably in the range of 20 to 50 nm.The nanogap of the metal nanoparticles is preferably in the range of 1 to 50 nm, more preferably in the range of 5 to 25 nm, and even more preferably in the range of 5 to 15 nm.

[0021] The average particle size may be measured by a laser diffraction method, and the nanogap may be measured by an image analysis measurement method.

[0022] The substrate having the metal nanoparticle layer is preferably used as a substrate for surface-enhanced Raman scattering. The metal nanoparticle layer is firmly attached to the substrate, and the substrate having the metal nanoparticle layer has excellent Raman scattering enhancement, uniformity, and high detection sensitivity comparable to commercially available SERS substrates. When the metal salt is silver nitrate, the silver nanoparticle layer adheres particularly firmly to the substrate. Furthermore, the manufacturing method of the substrate having the metal nanoparticle layer of the present invention does not require expensive equipment or advanced operating techniques, so the substrate having the metal nanoparticle layer can be manufactured inexpensively (the price of the substrate having the metal nanoparticle layer is about 1 / 170 of the price of a conventional SERS substrate) and in a short time. [Example]

[0023] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0024] In the examples and comparative examples, various physical properties were measured or calculated as follows. <Average particle size of silver nanoparticles> The projected diameter of the silver nanoparticles was measured as the particle size using high-magnification (×200,000) field-emission scanning electron microscope images and image analysis software. The number of samples was 100.

[0025] <Nanogap> The distance between nanoparticles was measured as the gap using high-magnification (×200,000) field-emission scanning electron microscope images of silver nanoparticles and image analysis software. The number of samples was 100.

[0026] [Example 1] An aqueous solution was prepared by dissolving 10% by mass of silver nitrate, 9.4% by mass of polyvinyl alcohol, and 0.014% by mass of platinum nanoparticles in pure water. The aqueous solution was applied at a concentration of 0.23 g / cm onto a 12 mm diameter glass substrate rotating at 6000 rpm. 2 A thin film was formed on the glass substrate. The glass substrate on which the thin film was formed was placed on a ceramic heater heated to 230°C, and the thin film and the glass substrate were heated in the atmosphere for 30 minutes to produce a SERS substrate. A layer of silver nanoparticles with an average particle diameter of 34 nm and a nanogap of 8.9 nm was formed on the glass substrate.

[0027] [Comparative Example 1] A thin film was formed on a glass substrate in the same manner as in Example 1, except that the glass substrate was not rotated. However, no silver nanoparticle layer was formed.

[0028] [Examples 2 to 4] SERS substrates were fabricated in the same manner as in Example 1, except that a synthetic mica substrate (Substrate A), a silicon substrate (Substrate B), and a sapphire substrate (Substrate C) were used instead of the glass substrate. Field-emission scanning electron microscope images of the silver nanoparticle layers on each of Substrates A to C (Figure 1) are shown, along with the relationship between the surface free energy of each substrate and the average particle size and nanogap of the silver nanoparticles (Figure 2). The upper part of the bar in Figure 2 represents the dispersive component of the surface free energy, and the lower part represents the polar component of the surface free energy. The surface free energy is calculated by the following formula (1). Surface free energy = dispersive component + polar component (1) The dispersion component is an energy component derived from van der Waals forces acting between molecules. The dispersion component is dominant between nonpolar molecules and is evaluated based on the hydrophobic and nonpolar properties of the substrate. The polar component is an energy component derived from polar interactions, such as dipole-dipole interactions and hydrogen bonds, acting between molecules. The polar component is evaluated based on the hydrophilic and polar properties of the substrate. The bonding between metal nanoparticles such as silver and the substrate (adhesion to the substrate) is thought to be dominated by interactions due to van der Waals forces. Therefore, the dispersion component of the surface free energy of the substrate is of interest.

Claims

1. 1. A method for manufacturing a substrate comprising a metal nanoparticle layer, comprising: a thin film forming step of forming a thin film on a substrate by spin coating a solution containing a metal salt, a water-soluble polymer, and a catalyst; The method for producing a substrate having a metal nanoparticle layer includes a reduction step of reducing the metal salt in the thin film obtained through the thin film formation step.

2. 2. The method for manufacturing a substrate having a metal nanoparticle layer according to claim 1, wherein the metal salt includes at least one selected from the group consisting of silver nitrate and gold chloride.

3. 2. The method for manufacturing a substrate having a metal nanoparticle layer according to claim 1, wherein the water-soluble polymer comprises polyvinyl alcohol.

4. 2. The method for manufacturing a substrate having a metal nanoparticle layer according to claim 1, wherein the catalyst comprises platinum.

5. 5. The method for manufacturing a substrate having a metal nanoparticle layer according to claim 1, wherein the substrate is a substrate used in a surface-enhanced Raman scattering method.

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