SERS substrate with gold and silver bilayer nanoarray structure and its preparation method

Abstract

This invention discloses a SERS substrate with a gold-silver bilayer nanoarray structure and its preparation method, belonging to the field of nanocomposite materials technology. The invention involves preparing a gold nanoparticle array via high-temperature rapid annealing, followed by copper film deposition using vacuum thermal evaporation, and finally obtaining the SERS substrate with the gold-silver bilayer nanoarray structure through chemical displacement in a silver nitrate solution. SERS performance testing results show that the detection limits of malachite green on both the silver nanoarray (AgNPs) and gold nanoarray (AuNPs) substrates are 10⁻⁶ and 10⁻⁶, respectively. ‑5 10 ‑4 The detection limit of malachite green on the SERS substrate of the gold-silver bilayer nanoarray structure can be reduced to 10 mol / L. ‑8 The concentration of mol / L indicates that the Au@Ag three-dimensional substrate of this invention has high sensitivity. The absorption curves and electric field distribution results of the FDTD simulation of the monolayer AuNPs substrate, the monolayer AgNPs substrate and the Au@Ag three-dimensional substrate show that the Au@Ag three-dimensional substrate exhibits a stronger local electromagnetic field enhancement effect compared with the monolayer AuNPs substrate and the monolayer AgNPs substrate.

Description

Technical Field

[0001] This invention belongs to the field of SERS substrate material technology, specifically relating to a gold-silver bilayer nanoarray structure SERS substrate and its preparation method. Background Technology

[0002] Surface-enhanced Raman spectroscopy (SERS) refers to the phenomenon where a sample is adsorbed onto the rough surface of colloidal metal particles such as gold, silver, or copper. Within the excitation region, the enhanced electromagnetic field at or near the sample surface leads to a significant increase in the Raman scattering signal of the adsorbed molecules compared to ordinary Raman scattering. Since its discovery, SERS has experienced rapid development in the last decade or so. The detection of analytes using SERS substrates can reach the micro-level, making these substrates widely applicable in SERS detection.

[0003] In existing technologies, noble metal nanostructures exhibit a significant SERS effect due to their localized surface plasmon resonance (LSPR) properties, offering considerable advantages in SERS applications. However, for silver nanostructures as SERS substrates, exposure to air leads to rapid oxidation, resulting in a weakened SERS effect. While gold nanostructures are more stable than silver nanostructures, their sensitivity is lower. Therefore, there is a need to develop a SERS substrate with both strong SERS effect and high sensitivity. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a SERS substrate with a gold-silver bilayer nanoarray structure and a method for preparing the same. The SERS substrate with a gold-silver bilayer nanoarray structure prepared by the method has a strong SERS effect and high sensitivity.

[0005] The technical solution adopted by this invention to solve its technical problem is as follows:

[0006] A method for preparing a SERS substrate with a gold-silver bilayer nanoarray structure includes the following steps:

[0007] (1) A gold film was sputtered on a silicon wafer by ion sputtering, and the silicon wafer covered with the gold film was subjected to vacuum high temperature rapid annealing to obtain a periodic gold nanosphere crown array.

[0008] (2) A copper film was deposited on the periodic gold nanosphere crown array by vacuum thermal evaporation to obtain a substrate;

[0009] (3) The substrate is immersed in AgNO3 solution to carry out a chemical displacement reaction to generate a silver nanoarray on the regularly arranged gold nanoparticles, thereby obtaining the SERS substrate with the gold-silver bilayer nanoarray structure.

[0010] Preferably, in step (1), the thickness of the gold film is 5 nm; in step (2), the thickness of the copper film is 5 nm.

[0011] Preferably, in step (1), the silicon wafer is cleaned before gold plating. The cleaning steps are: ultrasonic cleaning with acetone for 10-20 minutes, followed by cleaning with alcohol and pure water. After cleaning, the silicon wafer is air-dried or dried at 20-100°C for later use.

[0012] Preferably, in step (1), the sputtering time is 5-60 seconds, the annealing temperature is 700-850℃, and the annealing time is 3-30 minutes.

[0013] Preferably, in step (3), the conditions for the chemical displacement reaction are as follows: the substrate is immersed in 0.01 mol / L AgNO3 solution for 10-60 minutes, then taken out, soaked in clean water for 1-10 minutes, and naturally dried to obtain the SERS substrate of the gold-silver bilayer nanoarray structure.

[0014] A gold-silver bilayer nanoarray structure SERS substrate was prepared using the above-described SERS substrate preparation method.

[0015] As can be seen from the above technical solution, this invention provides a SERS substrate with a gold-silver bilayer nanoarray structure and its preparation method. Compared with the prior art, its advantages are as follows: This invention prepares a gold nanoparticle array using a high-temperature rapid annealing method, then deposits a copper film using a vacuum thermal evaporation method, and finally obtains the SERS substrate with the gold-silver bilayer nanoarray structure by chemical displacement in a silver nitrate solution. By growing silver nanoparticles on the gold nanoparticle array, the substrate structure is transformed from a two-dimensional structure to a three-dimensional structure, forming an array structure with spatial regularity, generating more "hot spots," exhibiting a stronger plasmon effect, and the three-dimensional structure has more spatial gaps, which makes it easier for probe molecules to accumulate on the surface of metal nanoparticles, thus giving this substrate a unique advantage in detecting low concentrations of analyte molecules. SERS performance test results show that the detection limits of malachite green on the silver nanoarray (AgNPs) substrate and the gold nanoarray (AuNPs) substrate are 10. -5 10 -4 The detection limit of malachite green on a SERS substrate with a gold-silver bilayer nanoarray structure can be reduced to 10 mol / L. - 8The concentration of mol / L indicates that the Au@Ag three-dimensional substrate of this invention has high detection sensitivity. FDTD simulations of the absorption curves and electric field distributions of monolayer AuNPs, monolayer AgNPs, and the Au@Ag three-dimensional substrate show that the Au@Ag three-dimensional substrate exhibits a stronger local electromagnetic field enhancement effect compared to monolayer AuNPs and monolayer AgNPs substrates. This invention provides a new method for developing novel, efficient, and stable three-dimensional plasma substrate materials, which can be used in water quality and food testing. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the fabrication process of the gold-silver bilayer nanoarray structure of the present invention.

[0017] Figure 2 These are SEM images of a single-layer AgNPs substrate and an Au@Ag three-dimensional substrate.

[0018] Figure 3 It is a histogram of frequency distribution of particle size and center-to-center distance in a single-layer AgNPs substrate.

[0019] Figure 4 This is a SERS image of surface-enhanced Raman spectroscopy (SERS) results of malachite green molecules on a monolayer AuNPs substrate, a monolayer AgNPs substrate, and an Au@Ag three-dimensional substrate.

[0020] Figure 5 These are absorption curves for a single-layer AuNPs substrate, a single-layer AgNPs substrate, and an Au@Ag three-dimensional substrate.

[0021] Figure 6 These are electric field distribution diagrams for a single-layer AuNPs substrate, a single-layer AgNPs substrate, and an Au@Ag three-dimensional substrate. Detailed Implementation

[0022] The technical solutions and effects of the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0023] The experimental materials and reagents of this invention are as follows: raw material malachite green (Tianjin Chemical Reagent Co., Ltd., analytical purity), silicon wafer (raw material, high-purity silicon, content greater than 99.99%), silver nitrate (Tianjin Chemical Pharmaceutical Co., Ltd., analytical purity), high-purity gold target (purity 99.99%), and high-purity copper target (purity 99.99%).

[0024] The experimental instruments used in this invention are as follows: a portable Raman spectrometer (i-Raman, B&W TEK), an ion sputtering coating machine (MCM-100, SECCO Co., Ltd., South Korea), a scanning electron microscope (Quanta 250, Thermo Fisher Scientific), a vacuum rapid annealing furnace (RTP-1200, ECOPIA, South Korea), a dedicated precision electronic balance (Class i, AL204, METTLER TOLEDO), and a vacuum thermal evaporator (VZZ-300, Beijing Weinuo Vacuum Technology Co., Ltd.).

[0025] This invention provides a method for preparing a SERS substrate with a gold-silver bilayer nanoarray structure, comprising the following steps:

[0026] (1) A gold film was sputtered on a silicon wafer by ion sputtering, and the silicon wafer covered with the gold film was subjected to vacuum high temperature rapid annealing to obtain a periodic gold nanosphere crown array.

[0027] (2) A copper film was deposited on the periodic gold nanosphere crown array by vacuum thermal evaporation to obtain a substrate;

[0028] (3) The substrate is immersed in AgNO3 solution to carry out a chemical displacement reaction to generate a silver nanoarray on the regularly arranged gold nanoparticles, thereby obtaining the SERS substrate with the gold-silver bilayer nanoarray structure.

[0029] This invention prepares a gold nanoparticle array using a high-temperature rapid annealing method, then deposits a copper film using a vacuum thermal evaporation method, and finally obtains a SERS substrate with the gold-silver bilayer nanoarray structure through chemical displacement in a silver nitrate solution. By growing silver nanoparticles on the gold nanoparticle array, the substrate structure is transformed from a two-dimensional structure to a three-dimensional structure, forming a spatially regular array structure. This generates more "hot spots," exhibiting a stronger plasmon effect. Furthermore, the three-dimensional structure has more spatial gaps, which allows probe molecules to be more easily enriched on the surface of the metal nanoparticles. Therefore, this substrate has unique advantages in detecting low concentrations of analyte molecules.

[0030] Specifically, in step (1), the thickness of the gold film is 5 nm; the thickness of the copper film is 5 nm.

[0031] Furthermore, in step (1), the silicon wafer is cleaned before gold plating. The cleaning steps are as follows: ultrasonic cleaning with acetone for 10-20 minutes, followed by cleaning with alcohol and pure water to remove impurities from the surface of the silicon wafer. After cleaning, the silicon wafer is air-dried naturally or dried at 20-100℃ for later use.

[0032] Specifically, in step (1), the sputtering time is 5-60 seconds, the annealing temperature is 700-850℃, and the annealing time is 3-30 minutes.

[0033] Specifically, in step (3), the conditions for the chemical substitution reaction are as follows: the substrate is immersed in 0.01 mol / L AgNO3 solution for 10-60 minutes, then taken out, soaked in clean water for 1-10 minutes, and naturally dried to obtain the SERS substrate of the gold-silver bilayer nanoarray structure.

[0034] Example 1: Fabrication of a SERS substrate with a gold-silver bilayer nanoarray structure

[0035] (1) Immerse the silicon wafer in acetone and ultrasonically clean it for 15 minutes, then clean it with alcohol and pure water respectively. After cleaning, let the silicon wafer air dry or dry it at 90°C for later use. Set the gold sputtering time of the ion sputtering coating instrument to 12 seconds, and sputter a gold film on the silicon wafer using the ion sputtering method. Place the silicon wafer covered with the gold film into a vacuum rapid annealing furnace and anneal it at 850°C for 5 minutes to obtain a periodic gold nanosphere crown array.

[0036] (2) The periodic gold nanosphere crown array was placed in a vacuum thermal evaporation coating instrument, and a 5 nm thick copper film was deposited by vacuum thermal evaporation to obtain the substrate;

[0037] (3) Immerse the substrate in 0.01 mol / L AgNO3 solution with the front side facing up. After soaking for 60 minutes, take it out, soak it in clean water for 1 minute, and let it dry naturally to obtain the SERS substrate of the gold and silver double-layer nanoarray structure, namely the Au@Ag three-dimensional substrate.

[0038] Comparative Example 1: Preparation of a monolayer AuNPs substrate

[0039] Immerse the silicon wafer in acetone and ultrasonically clean for 15 minutes, then clean it with alcohol and pure water respectively. After cleaning, let the silicon wafer air dry or dry it at 90°C for later use. Set the gold sputtering time of the ion sputtering coating instrument to 12 seconds and sputter a gold film on the silicon wafer using the ion sputtering method. Place the silicon wafer covered with the gold film in a vacuum rapid annealing furnace and anneal it at 850°C for 5 minutes. After the furnace temperature drops to room temperature, take out the sample to obtain a single-layer AuNPs substrate.

[0040] Comparative Example 2: Preparation of Monolayer AgNPs Substrates

[0041] The silicon wafer was immersed in acetone and ultrasonically cleaned for 15 minutes, then cleaned with alcohol and pure water respectively. After cleaning, the silicon wafer was air-dried or dried at 90℃ for later use. The silicon wafer sample was placed in a vacuum thermal evaporation coating instrument and a 5nm thick copper film was deposited by vacuum thermal evaporation. Then, the silicon wafer covered with the copper film was immersed in 0.01mol / L AgNO3 solution with the front side facing up. After immersion for 60 minutes, it was taken out, soaked in clean water for 1 minute, and then air-dried to obtain a single-layer AgNPs substrate.

[0042] The microstructure of the Au@Ag three-dimensional substrate prepared in the embodiments of the present invention and the monolayer AgNPs substrate prepared in Comparative Example 2 were characterized by SEM. The results are as follows: Figure 2 As shown, Figure 2 In the images: (a) is a SEM image of an AgNPs substrate (scale bar 500 nm); (b) is a SEM image of an Au@Ag 3D substrate (scale bar 500 nm); (c) is a SEM image of an AgNPs substrate (scale bar 150 nm); (d) is a SEM image of an Au@Ag 3D substrate (scale bar 150 nm). See also... Figure 2 In (a) and (c), on the copper film deposited on the silicon wafer, most of the silver nanoparticles on the monolayer AgNPs substrate obtained through chemical displacement exist in pairs. The paired particles are very close together, while the distance between the particle pairs is relatively large, which is related to the reaction process of the displacement reaction. See also Figure 2 In (b) and (d), an array structure resembling "stalactites" exists on the Au@Ag three-dimensional substrate. Most particles exhibit regular and orderly morphological arrangements, which is related to the high-temperature rapid annealing of the AuNPs. According to the principle of morphological continuity, self-grown particles will inherit the morphology of the AuNPs obtained through high-temperature rapid annealing. Compared to monolayer AgNPs, the Au@Ag three-dimensional substrate exhibits a greater number of nanoparticles, more regular morphology, and a more ordered arrangement.

[0043] Statistical analysis of the particle size and center-to-center distance of monolayer AgNPs substrates was performed using ImagJ software. The results are as follows: Figure 3 As shown, Figure 3 In the middle: (a) corresponds to the particle size distribution; (b) corresponds to the particle center distance distribution; see also Figure 3 (a) The average particle size of silver nanoparticles on a monolayer AgNPs substrate is 98.35 ± 21.05 nm. Statistical analysis of the center-to-center distance of the nanoparticles shows a single normal distribution. See also Figure 3 (b) The average core length of the monolayer AgNPs substrate is 113.05 nm.

[0044] The SERS performance of samples from Example 1, Comparative Example 1, and Comparative Example 2 was analyzed using a portable Raman spectrometer. Malachite green was selected as the probe molecule. Before detection, monolayer AuNPs substrates, monolayer AgNPs substrates, and Au@Ag three-dimensional substrates were immersed in an aqueous solution of malachite green for 2 hours, respectively, to allow malachite green molecules to be fully adsorbed onto the nanoparticles on the substrate surface. Then, the surface-enhanced Raman spectra of malachite green molecules on the three substrates were detected using a portable Raman spectrometer. The test conditions were: laser wavelength 785 nm and deposition time 15 s. The results are as follows: Figure 4 As shown, Figure 4(a) SERS detection of malachite green on AuNPs substrate; (b) SERS detection of malachite green on AgNPs substrate; (c) SERS detection of malachite green on Au@Ag 3D substrate. At 145cm -1 Up to 1800cm -1 Within the wavenumber range, the characteristic peak of malachite green molecules is 228.93 cm⁻¹. -1 422.06cm -1 440.09cm -1 730.86cm -1 752.06cm -1 798.38cm -1 916.4cm -1 938.86cm -1 1171.36cm -1 1217.67cm -1 1295.72cm -1 1366.89cm -1 1396.52cm -1 1491.51cm -1 1589.81cm -1 1616.24cm -1 The out-of-plane bending vibration of C-H (798.38 cm) -1 Radial vibration of the ring skeleton (916.4cm) -1 In-plane bending vibrations (1171.36, 1217.67 cm) -1 ), stretching vibration of the benzene ring (1366.89, 1396.52 cm). -1 ) and C-C stretching vibrations (1295.72, 1589.81, 1616.24 cm) -1 This data is consistent with numerous reported studies on the Raman characteristic peaks of malachite green molecules and can serve as a basis for the qualitative detection of malachite green molecules. Other interfering peaks are present in the detection graph, such as at 522.66 cm⁻¹. -1 This is a characteristic peak for silicon (Si), at 623.4 cm⁻¹. -1 The peak introduced by the silver nitrate solution. See also Figure 4 (a) The detection limit for malachite green molecules on a monolayer AuNPs substrate is 10. -4 mol / L; Figure 4 (b) The detection limit for malachite green molecules on a monolayer AgNPs substrate is 10. -5 mol / L; Figure 4 (c) The detection limit for malachite green molecules on the Au@Ag three-dimensional substrate reaches 10. -8The concentration of mol / L indicates that the Au@Ag three-dimensional substrate exhibits the SERS effect. This is mainly related to the localized surface plasmon resonance effect of gold and silver nanoparticles. The detection limit of the Au@Ag three-dimensional substrate is 4 orders of magnitude lower than that of the monolayer AuNPs substrate and 3 orders of magnitude lower than that of the monolayer AgNPs substrate. This is because the self-growth of Ag nanoparticles on the AuNPs substrate transforms the substrate structure from a two-dimensional structure to a three-dimensional structure, forming a spatially regular array structure and generating more "hot spots".

[0045] Absorption curves and electric field distributions of monolayer AuNPs substrates, monolayer AgNPs substrates, and Au@Ag three-dimensional substrates were simulated using FDTD. The absorption curve results are shown below. Figure 5 As shown, Figure 5 In the diagram: Line a, the absorption peak of the AuNPs substrate is located at 524 nm, indicating that the prepared AuNPs substrate exhibits a localized surface plasmon resonance (SERS) effect, validating the SERS effect observed in the experiment. Line b, the absorption peak of the AgNPs substrate is located at 400 nm, indicating that the prepared AgNPs substrate exhibits a localized surface plasmon resonance (SERS) effect, validating the SERS effect observed in the experiment. Line c, the absorption curve of the Au@Ag three-dimensional substrate shows two peaks, located at 393 nm and 534 nm respectively, corresponding to the absorption characteristics of gold and silver. These results demonstrate that the prepared Au@Ag three-dimensional substrate exhibits a localized surface plasmon resonance (SERS) effect, validating the SERS effect observed in the experiment. Compared with monolayer AuNPs and monolayer AgNPs substrates, the Au@Ag three-dimensional substrate exhibits stronger absorption characteristics, indicating a stronger localized surface plasmon resonance (SERS) effect.

[0046] The electric field distribution results are as follows Figure 6 As shown, Figure 6 In the images: (a) Electric field distribution on the bottom surface of a monolayer AuNPs substrate; (b) Electric field distribution on the bottom surface of gold pillars in an Ag@Au 3D array; (c) Electric field distribution on the top surface of a monolayer AgNPs substrate; (d) Electric field distribution on the top surface of silver pillars in an Ag@Au 3D array. See also: Figure 6 (a) The electric field on the surface of the monolayer AuNPs accumulates along the polarization direction of the light source, exhibiting a localized surface plasmon resonance effect, verifying the SERS effect observed in the experiment on the monolayer AuNPs substrate. See also Figure 6(c) The electric field accumulates on the surface of the monolayer AgNPs along the polarization direction of the light source, exhibiting a localized surface plasmon resonance effect, verifying the SERS effect observed in the experiment on the monolayer AgNPs substrate. The monolayer AgNPs substrate exhibits a stronger electric field enhancement effect along the polarization direction of the light source than the monolayer AuNPs substrate. This is because the plasmon resonance effect of silver is superior to that of gold, verifying that the detection limit of the monolayer AgNPs substrate is lower than that of the monolayer AuNPs substrate observed in the experiment. See also Figure 6 (b) Along the polarization direction of the light source, the electric field accumulates on the surfaces of the gold and silver pillars of the Au@Ag three-dimensional substrate, exhibiting a localized surface plasmon resonance effect, verifying the SERS effect observed in the experiment on the Au@Ag three-dimensional substrate. (Comparison) Figure 6 As shown in (a) and (b), the gold surface of the Au@Ag three-dimensional substrate exhibits a stronger electric field concentration along the light source polarization direction than the gold surface of the monolayer AuNPs substrate. This verifies the experimental observation that the detection limit of the Au@Ag three-dimensional substrate is lower than that of the monolayer AuNPs substrate. (Comparison) Figure 6 (c) and (d) show that the silver top surface of the Au@Ag 3D substrate exhibits a stronger electric field enhancement along the light source polarization direction than the silver top surface of the monolayer AgNPs substrate. This verifies that the detection limit of the Au@Ag 3D substrate is lower than that of the monolayer AgNPs substrate observed in the experiment. The above electric field distribution simulation results indicate that the Au@Ag 3D substrate exhibits a stronger plasmon effect compared to the monolayer AuNPs substrate and the monolayer AgNPs substrate, thus reducing the detection limit.

[0047] The above-disclosed embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the invention. Those skilled in the art will understand that implementing all or part of the above-described embodiments and making equivalent changes in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A method for preparing a SERS substrate with a gold-silver bilayer nanoarray structure, characterized in that: The method comprises the following steps: (1) a gold film is sputtered on a silicon substrate by ion sputtering, and vacuum high-temperature rapid annealing is performed on the silicon substrate covered with the gold film to obtain a periodic gold nanosphere crown array; (2) a copper film is evaporated on the periodic gold nanosphere crown array by vacuum thermal evaporation to obtain a substrate; (3) the substrate is immersed in an AgNO3 solution for chemical displacement reaction to generate a silver nanometer array on the regularly arranged gold nanometer to obtain the SERS substrate with the gold-silver double-layer nanometer array structure; in the step (1), the thickness of the gold film is 5 nm; in the step (2), the thickness of the copper film is 5 nm; in the step (1), the sputtering time is 5-60 seconds, the annealing temperature is 700-850 ℃, and the annealing time is 3-30 minutes; in the step (3), the chemical displacement reaction is performed by immersing the substrate in an AgNO3 solution with a concentration of 0.01 mol / L for 10-60 minutes, then taking out the substrate, immersing it in clean water for 1-10 minutes, and naturally drying to obtain the SERS substrate with the gold-silver double-layer nanometer array structure.

2. The method for preparing the SERS substrate of gold-silver double-layer nanoarray structure according to claim 1, characterized in that: in the step (1), the silicon substrate is cleaned before being plated with the gold film, and the cleaning step is as follows: ultrasonic cleaning with acetone for 10-20 minutes, then cleaning with alcohol and pure water, and naturally air-drying or drying at 20-100 ℃ after cleaning for standby.

3. The SERS substrate with the gold-silver double-layer nanometer array structure prepared by the preparation method according to any one of claims 1-2.

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