An optimized preparation method for a highly stable composite nanostructured SERS substrate

Abstract

The invention belongs to the technical field of SERS substrate preparation, and specifically relates to an optimized preparation method of a high-stability composite nanostructure SERS substrate, the steps of which include obtaining three-dimensional morphological feature data of a nano-rough surface; using simulation software to complete the establishment of an overall physical model of the composite substrate, setting its material properties and initial conditions for simulation, dividing the grid, and performing solution calculations; selecting processing parameters to prepare a nano-rough surface of transition metal oxide TiO2; combining an ultrasonic field with a laser ablation method to composite gold nanosphere particles on the nano-rough surface of transition metal oxide TiO2 to obtain a composite nanostructure SERS substrate; evaluating SERS activity through Raman spectroscopy to complete the preparation of the substrate. The invention can increase the contact points between the gold nanospheres and the surface, thereby increasing the nano-narrow slit structure on the substrate, and further improving the density of "hot spots" and detection intensity of the SERS substrate.

Description

Technical Field

[0001] The invention belongs to the technical field of SERS substrate preparation, and in particular relates to an optimized preparation method of a high-stability composite nanostructure SERS substrate. Background Art

[0002] Surface enhanced Raman scattering (SERS) is an in-situ, non-destructive detection technology with the advantages of high sensitivity, accurate fingerprint identification of target molecules, and real-time rapid detection on site. Therefore, SERS technology has become one of the methods with great application potential and research value in trace detection fields such as environmental testing, food safety, and biomedicine. The core of SERS is the interaction between light, nanostructures, and the substance to be tested. When the incident laser irradiates the surface of the SERS substrate, it will cause the collective oscillation of free electrons on the surface of nanoparticles or nanoscale gaps, generating surface plasmon resonance (LSPR). This process greatly enhances the local electric field and forms a "hot spot" around the nanoparticles or nanoscale gaps. The incident light intensity experienced by the molecules to be tested close to or adsorbed on the hot spot will be greatly enhanced, thereby stimulating its Raman effect.

[0003] Currently, the most common substrate materials that can produce SERS effect are: one is precious metal surface, such as gold and silver; the second is transition metal or transition metal oxide surface, such as TiO2 and Cu2O. Although most SERS substrates are based on precious metals, their high price and poor biocompatibility have greatly limited their application and development in SERS. As an emerging oxide substrate, transition metal oxides have attracted widespread attention due to their wide sources, good biocompatibility and stability.

[0004] In order to prepare a SERS substrate with better performance, we can consider breaking through the conventional thinking of using only noble metals or transition metal oxides as SERS substrates, and designing a nano-heterogeneous SERS substrate with the synergistic effect of transition metal oxide nano-rough surface and noble metal nanospheres. This structure can obtain many new properties. First, the multiple contact points between the nanospheres and the rough surface can be used to enhance the local surface plasmon resonance coupling effect, thereby increasing the density of the substrate "hot spots"; in addition, the chemical enhancement effect of transition metal oxides can be fully utilized; finally, the numerous contact points between the nanospheres and the rough surface enhance the stability and reliability of the heterostructure SERS substrate. As a typical optical material, TiO2 has super strong absorption and catalytic ability, which makes people continue to explore its related applications in SERS. The SERS substrate is realized by uniformly compounding gold nanospheres on the TiO2 nano-rough surface. This SERS substrate design scheme coordinates multiple mechanism advantages. In addition, most of the previous SERS substrate design optimizations are single-factor optimizations, and the designed SERS substrate is not the optimal configuration of the substrate parameters (geometric characteristics, material properties, physical fields). Therefore, it is possible to consider using simulation technology to obtain a structural optimization solution through multi-factor, multi-objective optimization simulation calculations, thereby guiding the selection of processing parameters during the preparation of the SERS substrate, and then performing Raman detection of the substance to be tested to complete the preparation of the nanoheterostructure SERS substrate. Summary of the invention

[0005] In view of the above deficiencies in the prior art, the purpose of the present invention is to provide an optimized preparation method for a high-stability composite nanostructured SERS substrate, which can increase the contact points between gold nanospheres and the surface, thereby increasing the nano-narrow slit structure on the substrate, and further improving the "hot spot" density and detection intensity of the SERS substrate.

[0006] To achieve the above objectives, the present invention provides an optimized preparation method of a high-stability composite nanostructure SERS substrate, comprising the following steps:

[0007] S1. Scan the nano-rough surface using an atomic force microscope to obtain three-dimensional morphological feature data of the nano-rough surface;

[0008] S2. Based on the three-dimensional morphological feature data, the two-dimensional geometric structure of the random nano-rough surface and the gold nanosphere composite SERS substrate is constructed using simulation software. The construction process includes the establishment of the two-dimensional random rough surface and the random contact between the gold nanosphere and the nano-rough surface, thereby completing the establishment of the overall physical model of the composite substrate;

[0009] S3, setting the material properties of the overall physical model of the composite substrate, and setting the initial conditions of the simulation, including wave equation parameters, scattering boundary conditions, periodic boundary conditions, and port conditions;

[0010] S4, dividing the grid for the overall physical model of the composite substrate, adding optimization calculation, setting the range of the objective function, control variables and constraints respectively, completing the solver settings, performing solution calculations, and obtaining optimization results;

[0011] S5. Based on the obtained optimization results, the selection of processing parameters in the preparation process of SERS substrate is deduced, and the nano-rough surface of transition metal oxide TiO2 is prepared;

[0012] S6, combining the ultrasonic field with the laser ablation method to composite gold nanosphere particles on the nano-rough surface of the transition metal oxide TiO2 to obtain a composite nanostructured SERS substrate;

[0013] S7. Immerse the composite nanostructure SERS substrate in weak affinity probe molecule melamine solutions of different concentrations, and then dry it naturally in a dust-free environment. After drying, evaluate the SERS activity by Raman spectroscopy to complete the preparation of the composite nanostructure SERS substrate.

[0014] As a preferred embodiment of the present invention, in the S1, a nano-rough surface (nanoscale rough surface) is produced by one of plasma high-temperature processing, atomic force scratching, micro-spark discharge, electron beam, and ion beam. After obtaining three-dimensional morphological feature data, the extreme value and average value of the height of the nano-rough surface are statistically analyzed as basic data for subsequent SERS substrate design and optimization.

[0015] As a preferred embodiment of the present invention, in S1, a 60 μm×60 μm area of ​​the nano-rough surface is scanned to obtain three-dimensional morphological feature data of the area in a tabular form, and 64 two-dimensional curve data are taken in the horizontal and vertical directions in the data table to obtain the maximum curve height H max , minimum value H min and mean H av , which are the extreme and mean values ​​of the nano-rough surface height.

[0016] As a preferred solution of the present invention, in S2, the “geometry tool” of COMSOL finite element simulation software is used to construct a two-dimensional geometric structure of a random rough surface and a gold nanosphere composite SERS substrate, and the construction process is:

[0017] S2.1. Use Gaussian Random function, Uniform Random function and "parameterized curve" coupling to establish a two-dimensional random rough surface.

[0018] S2.2, randomly arrange the random contacts between the gold nanospheres and the nano-rough surface according to the density of the gold nanospheres, and then apply “entity conversion” to construct a physical model of the SERS substrate;

[0019] S2.3. Construct an overall physical model of the composite substrate including the upper dielectric region, the lower SERS substrate region and the perfect matching layer region at the edge, and complete the construction of the two-dimensional geometric structure of the random rough surface and gold nanosphere composite SERS substrate.

[0020] As a preferred embodiment of the present invention, in S3, in the "Material" interface of the model builder in COMSOL, the two-dimensional random rough surface material is set to be a transition oxide TiO2 material, the nanospheres are set to be a gold material, the upper dielectric region is set to be air, and the edge perfectly matched layer region is set to be air;

[0021] When setting the initial conditions for the simulation, set the wave equation parameters including wavelength, frequency, electromagnetic properties of the medium, refractive index, polarization of the electromagnetic wave, and incident angle of the electromagnetic wave; select the "Electromagnetic Wave Frequency Domain" interface and set the "three-component vector" scattering field; the upper and lower sides of the overall physical model of the composite substrate are scattering boundary conditions, the left and right sides are periodic boundary conditions, and the internal upper and lower boundaries are set as port conditions.

[0022] As a preferred embodiment of the present invention, in the S4, right-click "Grid" in the model builder in COMSOL, select the "User Controlled Grid" sequence to divide the grid, add "Optimization Calculation" in the "Study 1" node of the model builder, and use the maximum field intensity and the minimum substrate reflectivity as "objective functions" respectively, and use the Gaussian Random function Gaussian Random seed, the uniform random function Uniform Random seed, the extreme value and average value of the random curve height, and the distribution density of the gold nanospheres as "control variables", and impose range constraints on each variable before solving the calculation.

[0023] As a preferred solution of the present invention, the range constraints on each variable are as follows: Gaussian Random function Gaussian Random seed constraint range 0.1~2, uniform random function Uniform Random seed constraint range 5~20, random curve height extreme value constraint range H min ~H max , Mean value constraint range-H av ~H av The distribution density of gold nanospheres is constrained to range from 2 (1 / μm) to 20 (1 / μm).

[0024] As a preferred embodiment of the present invention, in S5, the optimal geometric parameters GaussianRandom seed number, uniform random function Uniform Random seed number, random curve height extreme value and average value, and gold nanosphere random density are converted into processing parameters of plasma high temperature processing, and the processing voltage is set to 60V, the pulse width is 5μs, and the pulse interval is 15μs, and the nano-rough surface of transition metal oxide TiO2 is prepared by plasma high temperature processing.

[0025] As a preferred embodiment of the present invention, in the S6, the method for compounding gold nanosphere particles on the nano-rough surface of transition metal oxide TiO2 is to compound 50nm gold nanosphere particles on the nano-rough surface of transition metal oxide TiO2, control the reaction temperature at 350~480℃, use isopropanol as a dispersant, and the mass ratio of isopropanol to gold block is in the range of 10:1~20:1; during the laser ablation process, the ultrasonic vibration table provides a frequency of 25~35kHz and an ultrasonic power of 100~180W, and the ultrasonic vibration generates an ultrasonic field, which synergizes with laser ablation to form gold nanosphere particles of uniform size and uniform distribution on the nano-rough surface of transition metal oxide TiO2.

[0026] As a preferred embodiment of the present invention, in said S7, the concentration of the weak affinity probe molecule melamine solution used is 10 -2 M~10 -8 M, immersion time was 30 min. When evaluating SERS activity by Raman spectroscopy, 532 nm laser excitation was used with a power of 1 mW and an exposure time of 25 s. The 679 cm -1 The characteristic peak of the Raman signal under the condition of melamine was found, and the relationship between the Raman signal intensity and the melamine concentration was obtained.

[0027] The simulation involved in the present invention can be performed by an electronic device, which includes a memory, a processor, and a computer program stored in the memory and executable on the processor, and the above-mentioned simulation calculation is realized by executing the software by the processor.

[0028] The beneficial effects of the present invention are:

[0029] The present invention considers the composite of a TiO2 surface with nano-roughness and gold nanospheres, which can increase the contact points between the gold nanospheres and the rough surface, thereby increasing the narrow gap "hot spots", further improving the hot spot density and sensitivity of the SERS substrate, while taking into account the retention and adhesion of the substance to be detected on the rough surface and the excellent optical properties of TiO2.

[0030] The present invention designs a design optimization method for a rough surface and nanosphere composite SERS substrate, elaborates on the design optimization process of the SERS substrate, uses atomic force scanning of the nano-machined surface as original data to carry out the design, and increases the contact points between the gold nanospheres and the surface by compounding the transition metal oxide nano-rough surface with gold nanospheres, thereby increasing the nano-narrow slit structure on the substrate, further improving the "hot spot" density and detection intensity of the SERS substrate.

[0031] The present invention fully considers the catalytic and chemical characteristics of the optical properties of the transition metal oxide SERS substrate, and can increase the substrate "hot spot" density by compounding with gold nanospheres, while considering the retention and adhesion of the substance to be detected on the rough surface; the SERS substrate design scheme coordinates the advantages of multiple mechanisms, and obtains a structural optimization scheme through optimization calculation, thereby guiding the selection of processing parameters during the preparation of the SERS substrate; it can provide a solution for optimizing the composite substrate of transition metal oxides and precious metal materials, especially providing an optimization scheme for the design of a composite SERS substrate with multiple "hot spot" densities. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the process of the present invention;

[0033] Figure 2 is a schematic diagram of the structure of a nano-rough surface in an embodiment of the present invention;

[0034] Figure 3 is a schematic diagram of the overall physical model of the composite substrate and its boundary conditions in an embodiment of the present invention;

[0035] Figure 4 is a diagram of the local electric field enhancement simulation result of the overall physical model of the composite substrate in an embodiment of the present invention;

[0036] Figure 5 is the Raman signal intensity detection result of melamine molecular solutions with different concentrations in the embodiment of the present invention;

[0037] Figure 6 1 is a graph showing the logarithmic relationship between the Raman signal intensity of the melamine molecule solution and the solution concentration in an embodiment of the present invention. DETAILED DESCRIPTION

[0038] The embodiments of the present invention are further described below in conjunction with the accompanying drawings:

[0039] like Figure 1 As shown, an optimized preparation method of a high-stability composite nanostructure SERS substrate comprises the following steps:

[0040] S1. Use an atomic force microscope to scan the nano-rough surface to obtain the three-dimensional morphological feature data of the nano-rough surface; the schematic diagram of the nano-rough surface is as follows Figure 2 As shown;

[0041] S2. Based on the three-dimensional morphological feature data, the two-dimensional geometric structure of the random nano-rough surface and the gold nanosphere composite SERS substrate is constructed using simulation software. The construction process includes the establishment of the two-dimensional random rough surface and the random contact between the gold nanosphere and the nano-rough surface, thereby completing the establishment of the overall physical model of the composite substrate;

[0042] S3, setting the material properties of the overall physical model of the composite substrate, and setting the initial conditions of the simulation, including wave equation parameters, scattering boundary conditions, periodic boundary conditions, and port conditions;

[0043] S4, dividing the grid for the overall physical model of the composite substrate, adding optimization calculation, setting the range of the objective function, control variables and constraints respectively, completing the solver settings, performing solution calculations, and obtaining optimization results;

[0044] S5. Based on the obtained optimization results, the selection of processing parameters in the preparation process of SERS substrate is deduced, and the nano-rough surface of transition metal oxide TiO2 is prepared;

[0045] S6. Combining the ultrasonic field with the laser ablation method, compounding gold nanosphere particles on the nano-rough surface of the transition metal oxide TiO2, to obtain a composite nanostructure SERS substrate (the substrate has high hot spot density, high sensitivity, and high stability);

[0046] S7. Immerse the composite nanostructure SERS substrate in weak affinity probe molecule melamine solutions of different concentrations, and then dry it naturally in a dust-free environment. After drying, evaluate the SERS activity by Raman spectroscopy to complete the preparation of the composite nanostructure SERS substrate.

[0047] In S1, a nano-rough surface is produced by one of plasma high-temperature processing, atomic force scratching, micro-spark discharge, electron beam, and ion beam. After obtaining the three-dimensional morphological feature data, the extreme and average values ​​of the nano-rough surface height are statistically analyzed as the basic data for the subsequent SERS substrate design and optimization.

[0048] Scan the 60μm×60μm area of ​​the nano-rough surface to obtain the three-dimensional morphological feature data of the area in a tabular form, and take 64 two-dimensional curve data in the horizontal and vertical directions in the data table to obtain the maximum curve height H max , minimum value H min and mean H av , which are the extreme and mean values ​​of the nano-rough surface height.

[0049] In S2, the “geometry tool” of COMSOL finite element simulation software was used to construct a two-dimensional geometric structure of a random rough surface and a gold nanosphere composite SERS substrate. The construction process was as follows:

[0050] S2.1. Use Gaussian Random function, Uniform Random function and "parameterized curve" coupling to establish a two-dimensional random rough surface.

[0051] S2.2, randomly arrange the random contacts between the gold nanospheres and the nano-rough surface according to the density of the gold nanospheres, and then apply “entity conversion” to construct a physical model of the SERS substrate;

[0052] S2.3. Construct an overall physical model of the composite substrate including the upper dielectric region, the lower SERS substrate region and the perfect matching layer region at the edge, and complete the construction of the two-dimensional geometric structure of the random rough surface and gold nanosphere composite SERS substrate.

[0053] In S3, in the "Material" interface of the COMSOL Model Builder, set the 2D random rough surface material to transition metal oxide TiO2 material, the nanospheres to gold material, the upper dielectric region to air (air domain), and the edge perfectly matched layer region to air;

[0054] When setting the initial conditions for the simulation, set the wave equation parameters including wavelength, frequency, electromagnetic properties of the medium, refractive index, polarization of the electromagnetic wave, and incident angle of the electromagnetic wave; select the "Electromagnetic Wave Frequency Domain" interface and set the "three-component vector" scattering field; the upper and lower sides of the overall physical model of the composite substrate are scattering boundary conditions, the left and right sides are periodic boundary conditions, and the internal upper and lower boundaries are set as port conditions.

[0055] The simulation process can also be implemented by using finite element simulation software such as ANSYS, ADINA, ABAQUS, MSC, Hyperworks, etc.

[0056] The schematic diagram of the overall physical model of the composite substrate and its boundary conditions is shown in Figure 3 As shown, Figure 3 In the example, the port condition includes port 1 and port 2.

[0057] In S4, right-click "Mesh" in the COMSOL model builder, select the "User Controlled Mesh" sequence to divide the mesh, add "Optimization Calculation" to the "Study 1" node in the model builder, set the maximum field intensity and the minimum substrate reflectivity as "objective functions", and set the Gaussian Random function Gaussian Random seed, uniform random function Uniform Random seed, random curve height extreme value and average value, and gold nanosphere distribution density as "control variables", and set range constraints on each variable, and then solve the calculation. The simulation results of the local electric field enhancement of the overall physical model of the composite substrate are shown in Figure 2. Figure 4 shown.

[0058] from Figure 4 It can be seen that the random contact between gold nanospheres and the nano-rough surface of transition metal oxide TiO2 will produce different local electric field enhancements. The largest local electric field is generated at the contact point and the nano-gap structure around the contact point. As the number of contact points increases, the nano-gap structure also increases to varying degrees. Therefore, the number of "hot spots" with high electromagnetic intensity that is a multiple or power exponential of the number of gold nanospheres will increase on the surface of the composite SERS substrate, which can greatly improve the SERS detection sensitivity.

[0059] The Gaussian random function, also known as the normal random function, generates random numbers that follow a normal distribution (Gaussian distribution). The uniform random function generates random numbers that follow a uniform distribution, that is, within a given interval, the probability of each number being selected is the same. The seed is a value that initializes the random number generator and is used to generate a sequence of random numbers.

[0060] The range constraints for each variable are as follows: Gaussian Random seed constraint range 0.1~2, Uniform Random seed constraint range 5~20, random curve height extreme value constraint range H min ~H max , Mean value constraint range-H av ~H av The distribution density of gold nanospheres is constrained to range from 2 (1 / μm) to 20 (1 / μm).

[0061] In S5, the optimal geometric parameters, including the number of seeds of Gaussian Random function, the number of seeds of Uniform Random function, the extreme and average values ​​of the height of random curve, and the random density of gold nanospheres, are converted into processing parameters of plasma high-temperature processing. The processing voltage is set to 60V, the pulse width is set to 5μs, and the pulse interval is set to 15μs. Plasma high-temperature processing is used to prepare the nano-rough surface of transition metal oxide TiO2.

[0062] Plasma thermal processing is a material processing technology that uses the high temperature and chemical activity of plasma to change the properties of the material surface, such as improving hardness, corrosion resistance and wear resistance, or for applications such as depositing thin films, surface cleaning and polishing.

[0063] In S6, the method for compounding gold nanosphere particles on the nano-rough surface of transition metal oxide TiO2 is as follows: compounding 50nm gold nanosphere particles on the nano-rough surface of transition metal oxide TiO2, controlling the reaction temperature at 350~480℃, using isopropanol as a dispersant, and the mass ratio of isopropanol to gold block is in the range of 10:1~20:1; during the laser ablation process, the ultrasonic vibration table provides a frequency of 25~35kHz and an ultrasonic power of 100~180W, and the ultrasonic vibration generates an ultrasonic field, which synergizes with laser ablation to form gold nanosphere particles of uniform size and uniform distribution on the nano-rough surface of transition metal oxide TiO2.

[0064] Laser ablation is to place a gold block in a liquid environment (deionized water or organic solvent) and irradiate the surface of the gold block with a high-energy laser pulse. The energy of the laser causes the atoms on the gold surface to instantly gain enough energy to break away from the matrix. These atoms quickly cool and aggregate in the liquid to form gold nanosphere particles. When laser ablation of gold is performed in deionized water, the water plays a role in limiting the diffusion and cooling of atoms, which helps to form nanospheres of relatively uniform size.

[0065] The ultrasonic field uses ultrasonic vibration frequency (wave frequency greater than 16000Hz) to make the reactor vibrate ultrasonically during the laser ablation of gold. The strong stirring and cavitation effect of the ultrasonic field causes the gold particles to be continuously impacted and dispersed during the formation process, inhibiting the excessive growth of nanoparticles. By selecting the appropriate vibration frequency and power, gold nanoparticles of ideal size can be produced.

[0066] In S7, the concentration of the weak affinity probe molecule melamine solution used was 10 -2 M~10 -8 M, immersion time was 30 min. When evaluating SERS activity by Raman spectroscopy, 532 nm laser excitation was used with a power of 1 mW and an exposure time of 25 s. The 679 cm -1 The characteristic peak of the Raman signal under the condition of melamine was obtained, and the relationship between the Raman signal intensity and the melamine concentration was obtained. Rosiglitazone, levofloxacin and the like can also be used as weak affinity probe molecules.

[0067] The concentrations of the tested melamine molecule solutions were 10 -2 M, 10 -3 M, 10 -4 M, 10 -5 M, 10 -6 M, 10 -7 M, 10-8 M, observation 679cm -1 The Raman signal characteristic peak under the condition of melamine molecular solution with different concentrations and the logarithmic relationship between Raman signal intensity and solution concentration are shown in Figure 2. Figure 5 and Figure 6 shown. Figure 5 and Figure 6 In the above, au stands for arbitrary unit, which is used to indicate the intensity of Raman spectral signals. Because the absolute intensity of Raman signals is affected by many factors such as the laser power of the instrument and the efficiency of the detector, au can be used to compare the relative intensity between different samples or different peaks of the same sample without considering these complex factors. This is mainly to facilitate the comparison of the relative strength of each spectral peak under the same experimental conditions. The Lg in Lg [concentration (M)] refers to the logarithm, specifically the common logarithm of the concentration (expressed in molar concentration M), which is a logarithm with a base of 10. From Figure 5 It can be seen that the optimized SERS substrate concentration test range is wide, and for melamine, a weak affinity substance that is difficult to detect, it can still be detected when the solution concentration is extremely low. Figure 6 It can be seen that there is a good linear relationship between the Raman signal intensity and the melamine concentration, which largely indicates that the designed nano-rough surface and gold nanosphere composite SERS substrate has good stability.

Claims

1. An optimized preparation method of a high-stability composite nanostructure SERS substrate, characterized in that The following steps are involved: S1. Scan the nano-rough surface using an atomic force microscope to obtain three-dimensional morphological feature data of the nano-rough surface; S2. Based on the three-dimensional morphological feature data, the two-dimensional geometric structure of the random nano-rough surface and the gold nanosphere composite SERS substrate is constructed using simulation software. The construction process includes the establishment of the two-dimensional random rough surface and the random contact between the gold nanosphere and the nano-rough surface, thereby completing the establishment of the overall physical model of the composite substrate; S3, setting the material properties of the overall physical model of the composite substrate, and setting the initial conditions of the simulation, including wave equation parameters, scattering boundary conditions, periodic boundary conditions, and port conditions; S4, dividing the grid for the overall physical model of the composite substrate, adding optimization calculation, setting the range of the objective function, control variables and constraints respectively, completing the solver settings, performing solution calculations, and obtaining optimization results; S5. Based on the obtained optimization results, the selection of processing parameters in the preparation process of SERS substrate is deduced, and the nano-rough surface of transition metal oxide TiO2 is prepared; S6, combining the ultrasonic field with the laser ablation method to composite gold nanosphere particles on the nano-rough surface of the transition metal oxide TiO2 to obtain a composite nanostructured SERS substrate; S7. Immerse the composite nanostructure SERS substrate in weak affinity probe molecule melamine solutions of different concentrations, and then dry it naturally in a dust-free environment. After drying, evaluate the SERS activity by Raman spectroscopy to complete the preparation of the composite nanostructure SERS substrate.

2. The optimized preparation method of a high-stability composite nanostructure SERS substrate according to claim 1, characterized in that: In the above-mentioned S1, a nano-rough surface is produced by one of plasma high-temperature processing, atomic force scratching, micro-spark discharge, electron beam, and ion beam. After obtaining three-dimensional morphological feature data, the extreme value and average value of the height of the nano-rough surface are statistically analyzed as basic data for subsequent SERS substrate design and optimization.

3. The optimized preparation method of a high-stability composite nanostructure SERS substrate according to claim 2, characterized in that: In S1, a 60 μm×60 μm area of ​​the nano-rough surface is scanned to obtain three-dimensional morphological feature data of the area in a tabular form, and 64 two-dimensional curve data are taken in the horizontal and vertical directions in the data table to obtain the maximum curve height H max , minimum value H min and mean H av , which are the extreme and mean values ​​of the nano-rough surface height.

4. The optimized preparation method of a high-stability composite nanostructure SERS substrate according to claim 1, characterized in that: In S2, the "geometry tool" of COMSOL finite element simulation software is used to construct a two-dimensional geometric structure of a random rough surface and a gold nanosphere composite SERS substrate, and the construction process is as follows: S2.

1. Use Gaussian Random function, Uniform Random function and "parameterized curve" coupling to establish a two-dimensional random rough surface. S2.2, randomly arrange the random contacts between the gold nanospheres and the nano-rough surface according to the density of the gold nanospheres, and then apply "solid conversion" to construct a SERS substrate solid physical model; S2.

3. Construct an overall physical model of the composite substrate including the upper dielectric region, the lower SERS substrate region and the perfect matching layer region at the edge, and complete the construction of the two-dimensional geometric structure of the random rough surface and gold nanosphere composite SERS substrate.

5. The optimized preparation method of a high-stability composite nanostructure SERS substrate according to claim 4, characterized in that: In the above S3, in the "Material" interface of the COMSOL model builder, the two-dimensional random rough surface material is set to be a transition oxide TiO2 material, the nanospheres are set to be a gold material, the upper dielectric region is set to be air, and the edge perfectly matched layer region is set to be air; When setting the initial conditions for the simulation, set the wave equation parameters including wavelength, frequency, electromagnetic properties of the medium, refractive index, polarization of the electromagnetic wave, and incident angle of the electromagnetic wave; select the "Electromagnetic Wave Frequency Domain" interface and set the "Three-Component Vector" scattering field; the upper and lower sides of the overall physical model of the composite substrate are scattering boundary conditions, the left and right sides are periodic boundary conditions, and the internal upper and lower boundaries are set as port conditions.

6. The optimized preparation method of a high-stability composite nanostructure SERS substrate according to claim 3, characterized in that: In the above S4, right-click "Mesh" in the model builder in COMSOL, select the "User Controlled Mesh" sequence to divide the mesh, add "Optimization Calculation" in the "Study 1" node of the model builder, use the maximum field intensity and the minimum substrate reflectivity as "objective functions", use the Gaussian Random seed, the uniform random function Uniform Random seed, the extreme and average values ​​of the random curve height, and the distribution density of the gold nanospheres as "control variables", and impose range constraints on each variable before solving the calculation.

7. The optimized preparation method of a high-stability composite nanostructure SERS substrate according to claim 6, characterized in that: The range constraints for each variable are as follows: Gaussian Random function seed constraint range 0.1~2, uniform random function seed constraint range 5~20, random curve height extreme value constraint range H min ~H max , Mean value constraint range-H av ~H av The distribution density of gold nanospheres is constrained to range from 2 (1 / μm) to 20 (1 / μm).

8. The optimized preparation method of a high-stability composite nanostructure SERS substrate according to claim 6, characterized in that: In the S5, the optimal geometric parameters Gaussian Random function Gaussian Random seed number, uniform random function Uniform Random seed number, random curve height extreme value and average value, and gold nanosphere random density are converted into processing parameters of plasma high temperature processing. The processing voltage is set to 60V, the pulse width is 5μs, and the pulse interval is 15μs. The nano-rough surface of transition metal oxide TiO2 is prepared by plasma high temperature processing.

9. The optimized preparation method of a high-stability composite nanostructure SERS substrate according to claim 1, characterized in that: In the S6, the method for compounding gold nanosphere particles on the nano-rough surface of transition metal oxide TiO2 is as follows: compounding 50nm gold nanosphere particles on the nano-rough surface of transition metal oxide TiO2, controlling the reaction temperature at 350~480℃, using isopropanol as a dispersant, and the mass ratio of isopropanol to gold block is in the range of 10:1~20:1; during the laser ablation process, the ultrasonic vibration table provides a frequency of 25~35kHz and an ultrasonic power of 100~180W, and the ultrasonic vibration generates an ultrasonic field, which synergizes with laser ablation to form gold nanosphere particles of uniform size and uniform distribution on the nano-rough surface of transition metal oxide TiO2.

10. The optimized preparation method of a high-stability composite nanostructure SERS substrate according to claim 1, characterized in that: In the above S7, the concentration of the weak affinity probe molecule melamine solution used is 10 -2 M~10 -8 M, immersion time was 30 min. When evaluating SERS activity by Raman spectroscopy, 532 nm laser excitation was used with a power of 1 mW and an exposure time of 25 s. The 679 cm -1 The characteristic peak of the Raman signal under the condition of melamine was found, and the relationship between the Raman signal intensity and the melamine concentration was obtained.

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