A method for preparing a SERS substrate by solution evaporation self-assembly and a substrate prepared thereby

Abstract

This invention relates to the field of nanomaterial preparation, specifically to the preparation of a composite silver nanowire-gold nanoparticle SERS substrate by sequentially dropping silver nanowire sol and gold nanoparticle sol onto a glass slide. The silver nanowires cover 60%–80% of the glass slide, while the gold nanoparticles cover 10%–90% of the silver nanowires. This method allows for convenient modification of experimental conditions to control the coverage of the silver mesh and gold nanoparticles, and to control the gaps of a few nanometers between the silver mesh and the gold nanoparticles, thereby adjusting the intensity and density of the "hot spots" to prepare various SERS substrates with different enhancement effects, improving SERS detection performance, and further ensuring the stability and repeatability of the substrate. The method of this invention does not involve large and expensive instruments, is simple and convenient, has a short cycle time, and is easy to further promote and apply.

Description

Technical Field

[0001] This invention belongs to the field of detection technology, specifically relating to a method for preparing SERS substrates through solution evaporation self-assembly and the substrates prepared therefrom. Background Technology

[0002] With the acceleration of human industrialization, frequent economic activities and pollutant emissions have caused serious environmental pollution, posing a significant threat to human health and sustainable environmental development. Therefore, establishing a rapid, real-time, and simple detection and analysis technology to track and detect environmental pollutants is of great significance in changing the severe safety and environmental protection situation. Among numerous detection technologies, surface-enhanced Raman spectroscopy (SERS) refers to a method in which, when light is incident on specially prepared nano-substrates or sols, the Raman scattering signal of adsorbed molecules is significantly enhanced compared to ordinary Raman signals due to the enhanced electromagnetic field on the surface of the nanostructure. As an emerging detection technology, SERS has advantages such as high sensitivity, rich chemical fingerprint information, simple operation, and the ability to achieve in-situ detection, and is widely used in materials, chemistry, biology, and medical detection and identification.

[0003] When nanoscale metal particles or array structures contain gaps of a few nanometers or smaller, these gaps can strongly couple with incident light, exciting localized surface plasmon resonances (LSPRs) or surface plasmon polaritons (SPPs) and confining the energy within them, forming a strong electromagnetic field enhancement region (also known as a "hot spot"). The enhancement effect of the SERS substrate depends on these "hot spot" regions on the surface of the structure. Therefore, appropriate fabrication methods can be selected to construct corresponding nano-reinforced substrates, forming a sufficient number of nano-gap gaps to increase the density of "hot spots." During the fabrication process, the shape, structure, size, and type of material of the substrate all affect the intensity and distribution of the electromagnetic field. Currently, various nanomaterials can be used to fabricate SERS substrates, such as gold nanospheres, gold nanorods, and silver nanowires. Commonly used methods for preparing SERS substrates fall into two categories: one is the nanoparticle sol-gel method or the drop-coating of nanoparticles onto the substrate. These methods are simple to operate, but the resulting nanostructures are relatively simple, and the enhancement effect needs improvement. The other is the top-down or bottom-up template method. This method produces substrates with highly controllable spatial structures, but it often involves expensive equipment such as plasma etching machines, vacuum coating machines, and even electron beam etching machines and focused ion beam etching machines, which hinders the large-scale application of these methods. Currently, research on preparing highly controllable three-dimensional nanostructured SERS substrates by combining silver nanowires and gold nanorods through solution evaporation self-assembly is relatively limited.

[0004] Several studies have reported on the preparation of SERS substrates using silver nanowires and gold nanoparticles. CN107101989A describes inducing the self-assembly of gold nanorod sol on a substrate via solvent evaporation to obtain an SERS substrate for drug detection. However, this method, based on single-material gold nanorods, relies on the LSPR effect of the gold nanorods as a hotspot. Compared to composite nanomaterial structures, the coupling effect is singular, resulting in fewer hotspots and requiring further improvement in signal enhancement. CN 111337474A describes preparing a composite micro / nano structure with gold and silver nanoparticles using metal hot rolling and wet etching techniques, and using it as a SERS substrate for the detection of rhodamine 6G. However, this method is complex, requires expensive equipment, has a long preparation cycle, and is not easily applicable. CN 109946285A describes using electrostatic adsorption to adsorb gold nanospheres onto silver nanowires to prepare a uniformly and densely arranged SERS substrate for the detection of the lung cancer biomarker miR-196a. These methods require strict control over the synthesis steps of gold nanoparticles and silver nanowires, thereby controlling the amount of charge on their surfaces. If the amount of charge is too high or too low, aggregation can easily occur when the gold nanoparticles and silver nanowires are mixed, making it impossible to prepare the appropriate substrate. Summary of the Invention

[0005] In view of the shortcomings of the prior art mentioned in the background, the purpose of this invention is to provide a method for preparing SERS substrates by solution evaporation self-assembly, and it is expected that this method can be used to prepare three-dimensional SERS substrates with silver nanowire-gold nanoparticle composite structures with different coverage.

[0006] This invention provides a method for preparing SERS substrates through solution evaporation self-assembly, comprising the following steps:

[0007] (1) Preparation of silver nanowire sol;

[0008] (2) Preparation of gold nanoparticle sol;

[0009] (3) Silver nanowire sol and gold nanoparticle sol were sequentially dropped onto a glass slide to prepare a composite silver nanowire-gold nanoparticle SERS substrate.

[0010] The silver nanowires cover 60%–80% of the glass slide; the gold nanoparticles cover 10%–90% of the silver nanowires.

[0011] The process of preparing the composite silver nanowire-gold nanoparticle SERS substrate in step (3) includes the following steps:

[0012] (31) Silver nanowire sol was dropped onto a glass slide and heated in an oven to obtain a glass slide with silver nanowires.

[0013] (32) Place the glass slide with silver nanowires obtained in step (31) on a hot plate and drop gold nanoparticle sol onto the glass slide with silver nanowires.

[0014] The silver nanowires have a length of 15–25 μm and a diameter of 20–40 nm. The gold nanoparticles are any one of gold nanorods, gold nanospheres, and gold nanotriangles, preferably gold nanorods. The gold nanorods have a length of 30–80 nm and a diameter of 10–40 nm. The gold nanospheres and gold nanotriangles have a particle size of 10–80 nm.

[0015] In step (32), the gold nanoparticle sol is added to the glass slide with silver nanowires in multiple drops, ranging from 1 to 10 times. The amount of gold nanoparticle sol added per unit area on the glass slide with silver nanowires each time is 30–40 μl / cm². 2 The concentration of the gold nanoparticle sol is 0.5–1.2 mg / ml; the heating temperature of the hot plate is 30–80 °C, and the liquid is heated until it evaporates completely.

[0016] In step (31), the amount of silver nanowire sol added per unit area on the glass slide is 20–80 μl / cm². 2 The concentration of the silver nanowire sol was 0.5–1.5 mg / ml; the oven temperature was 40–70 °C, and the liquid was heated until it evaporated completely.

[0017] Furthermore, the glass slide in step (31) needs to be pretreated. The pretreatment steps are as follows: the glass slide is washed with piranha solution (a mixed solution of concentrated sulfuric acid and 30% hydrogen peroxide in a volume ratio of 2:3 to 10:3), then washed with acetone, ethanol and deionized water respectively, and finally dried with nitrogen to obtain a clean glass slide.

[0018] The process of preparing silver nanowire sol in step (1) includes the following steps:

[0019] (11): Dissolve polyvinylpyrrolidone (PVP) in ethanol and stir to form a clear solution;

[0020] (12): Add silver nitrate AgNO3 to the clear solution of step (11), seal the reaction, centrifuge and wash to obtain silver nanowire sol.

[0021] In step (11), polyvinylpyrrolidone, abbreviated as PVP, has a weight-average molecular weight M. W It is 55,000;

[0022] In step (12), the weight ratio of silver nitrate (AgNO3) to PVP in step (11) is 1:15 to 1:20. The reaction vessel in step (12) is a hydrothermal reactor, the sealed reaction temperature is 140 to 170°C, the reaction time is 4 to 8 hours, the centrifugation speed is 3000 to 6000 r / min, and the centrifugation time is 3 to 7 minutes.

[0023] The preparation of the gold nanoparticle sol in step (2) follows the conventional preparation method for gold nanomaterials.

[0024] Furthermore, the gold nanoparticle sol is a gold nanorod sol, and its preparation process includes the following steps:

[0025] (21): Prepare a seed solution containing HAuCl4, hexadecyltrimethylammonium bromide CTAB and NaBH4, wherein the molar ratio of HAuCl4, CTAB and NaBH4 in the seed solution is 1:380~400:2~3;

[0026] (22): Prepare a growth solution containing HAuCl4, AgNO3, CTAB and ascorbic acid, wherein the molar ratio of HAuCl4, AgNO3, CTAB and ascorbic acid is 5:1~2:900~1100:7~12;

[0027] (23): Add the seed solution prepared in step (21) to the growth solution in step (22), mix, let stand, centrifuge, and obtain gold nanorod sol.

[0028] Furthermore, in step (22), when preparing the growth solution, HAuCl4, AgNO3 and CTAB are mixed first, then the pH of the solution is adjusted to 1-2, and then ascorbic acid is added.

[0029] In step (23), the settling time is 8 to 12 hours; the centrifugation speed is 4000 to 7000 r / min and the time is 8 to 12 minutes.

[0030] In another aspect, the present invention provides a SERS substrate for a silver nanowire-gold nanoparticle composite structure prepared by the above method.

[0031] Conventional methods for preparing gold-silver composite nanomaterials involve mixing the nanomaterials first and then coating them. However, a problem arises during mixing: the charged components of the nanomaterials can easily cause aggregation, leading to uneven mixing. This is because reducing agents and surfactants are added during the synthesis of gold and silver nanomaterials, resulting in charged particles. If the charges on the two mixed particles are unsuitable, aggregation occurs. To avoid this, the particles must be resynthesized, adjusting the type and amount of charge.

[0032] The preparation method of the present invention includes the following steps: Figure 1 As shown, the stepwise coating of silver nanowires and gold nanoparticles avoids the "agglomeration" phenomenon. This method allows for convenient modification of experimental conditions. By adjusting the type and morphology of the nanomaterials, as well as the concentration and number of drops of the corresponding sol, the density of the silver nanowires and gold nanoparticles can be controlled. This controls the coverage of the silver mesh formed by the silver nanowires and the gold nanoparticles, and the formation of gaps of a few nanometers between the silver mesh and the gold nanoparticles. This allows for the adjustment of the intensity and density of "hot spots," thus preparing various SERS substrates with different enhancement effects, improving SERS detection performance, and further ensuring the stability and repeatability of the substrate. The method of this invention does not involve large and expensive instruments such as etching machines and coating machines. It is simple, convenient, has a short preparation cycle, and is low in cost, facilitating further promotion and application. Attached Figure Description

[0033] Figure 1 A schematic diagram of the preparation process of the silver nanowire-gold nanoparticle SERS substrate;

[0034] Figure 1 In the image, 1 represents a glass substrate, 2 represents silver nanowires, and 3 represents gold nanoparticles.

[0035] Figure 2A and 2B Scanning electron microscope (SEM) images of the silver nanowire mesh substrates of Example 1 and Comparative Example 2;

[0036] Figure 3A and Figure 3B This is a scanning electron microscope image of the SERS-1 substrate from Example 1;

[0037] Figure 4A and Figure 4B Here is a scanning electron microscope image of the SERS-2 substrate from Example 2;

[0038] Figure 5A and Figure 5B Here is a scanning electron microscope image of the SERS-3 substrate from Example 3;

[0039] Figure 6 The concentration is 10 -6 Raman signal intensity diagrams of Rhodamine 6G molecule M under different nanomaterial SERS substrates in Examples 1-3 and Comparative Examples 1-2 under different nanomaterial SERS substrates;

[0040] Figure 7 The concentration is 10 -6 Raman signal intensity map of Rhodamine 6G molecule M under SERS-4 substrate in Example 4;

[0041] Figure 8Raman signal intensity maps of thiamethoxam bimolecules detected at 20 different locations on the SERS-1 substrate prepared in Example 1;

[0042] Figure 9 The levels of thiram bimolecules detected at 933 cm⁻¹ at 20 different locations on the SERS-1 substrate prepared in Example 1 were analyzed. -1 and 1387cm -1 Raman intensity at the characteristic peak. Detailed Implementation

[0043] The technical solution of the present invention is further described below with reference to embodiments and accompanying drawings, but these embodiments do not limit the scope of protection of the present invention. In the following embodiments and comparative examples, a high-resolution scanning electron microscope (SEM) of model JCM-7000 was used for detection, with an electron beam voltage of 5KV and a focal length of 9.8mm. Raman signals were measured using a Horiba Xplus microconfocal Raman spectrometer. During the test, a 633nm laser was used for irradiation, with a laser power of 0.1mW, an integration time of 20s, and two integration cycles.

[0044] The following examples are based on Figure 1 A schematic diagram illustrating the preparation process of the silver nanowire-gold nanoparticle SERS substrate. Figure 1 First, silver nanowires are dropped onto a glass substrate to form a silver nanowire network, and then gold nanoparticles are dropped onto the glass substrate containing the silver nanowires. Figure 1 In the diagram, 1 represents a glass substrate, 2 represents silver nanowires, and 3 represents gold nanoparticles.

[0045] Example 1

[0046] 1. Synthesis of silver nanowire sol: First, 0.3g of polyvinylpyrrolidone (PVP, M...) was added... W =55,000) was added to 35 mL of ethanol, and stirred for 30 minutes to form a clear solution. Then, 0.017 g of AgNO3 was added, and the mixture was stirred vigorously for 10 minutes. The mixture was then transferred to a hydrothermal reactor (50 mL) and sealed at 165 °C for 6 hours. After the reaction, the mixture was centrifuged at 4000 r / min for 5 minutes, repeated three times, to wash away unreacted raw materials, yielding an ethanol sol of silver nanowires with a diameter of 20 nm and a length of 20 μm.

[0047] 2. Synthesis of gold nanorod sol: First, HAuCl4 solution (0.01M, 0.25mL) and CTAB solution (0.1M, 9.75mL) were mixed evenly in a 15mL plastic tube. Then, NaBH4 solution (0.01M, 0.6mL) was added to this mixture as a seed solution. Next, HAuCl4 (0.01M, 2.0mL), AgNO3 (0.01M, 0.4mL), and CTAB (0.1M, 40mL) were mixed. Then, HCl (1.0M, 0.8mL) was added to adjust the pH of the solution to 1.5, and ascorbic acid (0.1M, 0.32mL) was added. Finally, the prepared seed solution (0.096mL) was added, gently mixed for 10s, and allowed to stand for 12h. Centrifugation at 5000rpm for 10min yielded gold nanorod sol with a diameter of 15nm and a length of 60nm.

[0048] 3. Clean the glass slide with piranha solution (a mixture of concentrated sulfuric acid and 30% hydrogen peroxide in a volume ratio of 7:3), then clean it with acetone, ethanol and deionized water respectively, and finally dry it with nitrogen gas to obtain a clean glass slide.

[0049] The treated glass slide was placed in a 50℃ oven, and 10 μl of 1.0 mg / ml silver nanowire sol was dropped onto a 0.5 cm * 0.5 cm glass slide. The amount of silver nanowire sol dropped per unit area on the glass slide was 40 μl / cm². 2 A three-dimensional silver nanowire network structure was obtained through solution evaporation self-assembly. This network structure serves as an excellent substrate for the subsequent gold nanorod assembly, playing a crucial role in the overall composite SERS substrate. Scanning electron microscopy (SEM) revealed that the silver nanowires covered 70% of the glass substrate. (SEM image shown below.) Figure 2A and 2B .

[0050] 4. Place the glass slide with silver nanowires from step 3 on a hot plate at 50°C. Add gold nanorod sol to the glass slide in nine separate drops. Each drop consists of 10 μl of 0.8 mg / ml gold nanorod sol, and the amount added per unit area is 40 μl / cm². 2 During the evaporation of the sol, gold nanorods are adsorbed onto the silver nanowires through capillary action and gravity. After the sol has completely evaporated, a second addition is made, resulting in a composite silver nanowire-gold nanorod network structure. Under these experimental conditions, substrate SERS-1 was obtained. Controlling the number of gold nanorod sol additions to nine times effectively regulates the density of gold nanorods in the composite structure. Scanning electron microscopy (SEM) observation showed that the gold nanorods covered 80% of the silver nanowires. The SEM image of substrate SERS-1 is shown below. Figure 3A and3B .

[0051] 5. Detection of environmental pollutants:

[0052] The prepared SERS-1 was used as a SERS substrate to detect the organic dye Rhodamine 6G. First, the SERS-1 was immersed in 10... -6 Rhodamine M 6G in an ethanol solution was analyzed using a Horiba Xplus microconfocal Raman spectrometer. During the test, a 633nm laser was used for irradiation with a laser power of 0.1mW, an integration time of 20s, and two integration cycles. The Raman signals are shown below. Figure 6 As shown in SERS-1.

[0053] Example 2

[0054] The preparation steps are the same as in Example 1, except that in step 3, the amount of silver nanowire sol added per unit area on the glass slide is 30 μl / cm². 2 The concentration of the silver nanowire sol was 1.2 mg / ml; the coverage of the silver nanowires on the glass substrate was 60%; in step 4, gold nanorod sol was added dropwise 6 times, with each dropwise amount of gold nanorod sol on the glass slide with silver nanowires being 8 μl, and the dropwise amount per unit area being 32 μl / cm2; the number of gold nanorods attached to the silver nanonetwork structure decreased, and the coverage of gold nanorods on the silver network was 50%, resulting in substrate SERS-2. The scanning electron microscope image is shown below. Figure 4A and 4B According to Example 1, sample 8 / 0.25 was used to detect the organic dye Rhodamine 6G. The Raman signal is shown in [reference needed]. Figure 6 As shown in SERS-2.

[0055] Example 3

[0056] The preparation steps were the same as in Example 1, except that the concentration of the gold nanorod sol was 0.5 mg / ml, added dropwise in three portions; the gold nanorods covered 30% of the silver nanowires, resulting in the substrate SERS-3. The scanning electron microscope image is shown below. Figure 5A and 5B The organic dye Rhodamine 6G was detected according to the conditions of Example 1, and the Raman signal is shown in [Figure 1]. Figure 6 As shown in SERS-3.

[0057] Example 4

[0058] The preparation steps were the same as in Example 1, except that gold nanorods were replaced with gold nanospheres in step 4. A silver nanowire-gold nanosphere substrate SERS-4 was obtained. Measurements were taken at 10... -6 The Raman signal of Rhodamine 6G in M, see Figure 7 As shown in SERS-4.

[0059] The gold nanospheres were prepared by adding 240 μl of a 0.2 mol / L chloroauric acid solution to 150 ml of water and heating to boiling while stirring at 850 rpm. Then, 2 ml of a 0.04 mol / L sodium citrate solution was quickly added, and the reaction was continued for 30 min. After cooling to room temperature, the mixture was centrifuged three times at 3000 rpm for 10 min to remove unreacted reactants, yielding a gold nanosphere sol. The gold nanospheres had a particle size of 20 nm.

[0060] Example 5

[0061] The preparation steps are the same as in Example 1, except that the gold nanorods in step 4 are replaced with gold nanotriangles, which are prepared according to the method described in patent CN102286280B; the particle size of the gold nanotriangles is 30 nm; a silver nanowire-gold nanotriangle substrate is obtained. Measurements were taken at 10... -6 The Raman signal of Rhodamine 6G M. The spectral shape and signal intensity are similar to those in Example 4.

[0062] Example 6

[0063] To demonstrate the repeatability and stability of the substrate, the substrate prepared in Example 1 was used to test 10... -7 The M-type thiamethoxam was tested. First, the substrate was placed in a 2ml centrifuge tube, and 10... -7 After soaking in an ethanol solution of thiram (M) for 4 hours, the substrate was removed, and the residual solution on the substrate was carefully absorbed with filter paper. Then, the substrate was gently agitated in ethanol, and excess ethanol was absorbed with filter paper. This process was repeated three times to remove molecules that failed to adsorb onto the substrate surface. Raman spectroscopy was performed at 20 different locations on the SERS-1 substrate, and the obtained Raman signals are shown below. Figure 8 As shown. Figure 8 It can be seen that the Raman signal intensity at 20 different locations is relatively consistent. Further selection at 933 and 1387 cm⁻¹... -1 20 intensities of the two characteristic peaks were made Figure 9 The relative labeling differences of the two characteristic peak intensities were calculated to be 2.7% and 1.7%, respectively. Therefore, this SERS substrate exhibits good repeatability and stability.

[0064] Comparative Example 1

[0065] Similar to Example 1, except that the gold nanorod sol and silver nanowire sol were mixed first. During the experiment, it was found that after the synthesized silver nanowire sol and gold nanorod sol were mixed, a significant aggregation phenomenon immediately occurred due to the electrostatic adsorption between the two.

[0066] To avoid aggregation, the charge level on the gold nanorod surface was adjusted. The preparation steps for the gold nanorods were the same as step 2 in Example 1, except that the CTAB in the growth solution was reduced to 0.1 M and 30 mL. Then, 1 mL of 1.0 mg / mL silver nanowire sol and 0.3 mL of 0.2 mg / mL gold nanorod sol were mixed and magnetically stirred for 30 min. A glass slide was placed in a 50°C oven, and 10 μL of the mixed solution was dropped onto the glass slide to prepare substrate D-1. Measurements were taken at 10... -6 The Raman signal of Rhodamine 6G in M, see Figure 6 As shown in D-1.

[0067] Comparative Example 2

[0068] The preparation was carried out in the same manner as in Example 1, steps 1-3, except for step 4, resulting in substrate D-2 consisting only of silver nanowire mesh. The scanning electron microscope image is shown below. Figure 2A and 2B , Measure 10 -6 The Raman signal of Rhodamine 6G in M, see Figure 6 As shown in D-2.

[0069] from Figure 6 , Figure 7 It can be seen that, with Rhodamine 6G at 1509cm -1 Taking the signal strength at a certain location as an example, the signal strength is shown in Table 1.

[0070] Table 1. Displacement of Rhodamine 6G in Raman tests on different substrates: 1509 cm -1 Strength at the point

[0071] base strength SERS-1 11610 SERS-2 11986 SERS-3 6439 SERS-4 8741 D-1 5796 D-2 1465

[0072] Depend on Figure 6 , Figure 7 As shown in Table 1, in Comparative Example 2, only the signal intensity D-2 of the silver nanowire network structure substrate was lower than that of the Example. This is because the plasmonic effect between the silver nanowires resulted in the fewest hot spots. In Comparative Example 1, this method requires strict control of the synthesis steps of gold nanoparticles and silver nanowires to control the amount of charge on their surfaces. If the amount of charge is too high or too low, agglomeration easily occurs when the gold nanoparticles and silver nanowires are mixed, making it impossible to prepare the corresponding substrate. By changing the surface charge of the gold nanorods to a suitable level with the surface charge of the silver nanowires, substrate D-1 was obtained after mixing. The signal intensity was measured at 10... -6 The Raman signal of Rhodamine 6G at 1509cm -1 The strength is 5796, which is lower than that of Examples 1-4 of this invention. The coverage of gold nanorods obtained by this method is not easy to adjust, which can easily cause charge imbalance and lead to aggregation.

[0073] The signal intensity of the SERS-2 substrate in Example 2 is higher than that of the SERS-3 substrate in Example 3 because the addition of gold nanorods generates corresponding plasmon effects between the silver nanowires and gold nanorods, as well as between the gold nanorods themselves, resulting in more hot spots and further enhancing the Raman signal. Furthermore, the gold nanorods are added to the silver mesh in multiple drops, and the particle distribution is relatively uniform as observed under scanning electron microscopy. As the coverage of gold nanorods on the silver nanowires gradually increases, the number and uniformity of hot spots generated by the gold nanorods increase. Further increasing the number of gold nanorods yields the SERS-1 substrate of Example 1, but the signal intensity remains essentially unchanged. This is mainly because the excessive coverage of gold nanorods leads to some accumulation, and the increase in hot spots is not significant.

[0074] As can be seen from Examples 1 to 6, the density of silver nanowires and gold nanoparticles can be controlled by adjusting the concentration, amount, and number of drops of the corresponding gold nanoparticle sol and silver nanowire sol; thereby controlling the coverage of the silver mesh and gold nanoparticles, and further controlling the formation of gaps of a few nanometers between the silver mesh and gold nanoparticles, thereby adjusting the intensity and density of the "hot spots". Various SERS substrates with different enhancement effects can be prepared to improve the SERS detection effect.

Claims

1. A method for preparing SERS substrates via solution evaporation self-assembly, characterized in that, Includes the following steps: (1) Preparation of silver nanowire sol; (2) Preparation of gold nanoparticle sol; (3) Silver nanowire sol and gold nanoparticle sol were sequentially dropped onto a glass slide to prepare a composite silver nanowire-gold nanoparticle SERS substrate; The silver nanowires cover 60% to 80% of the glass slide; the gold nanoparticles cover 50% to 90% of the silver nanowires. The gold nanoparticles are gold nanorods; the length of the gold nanorods is 30~80nm and the diameter is 10~40nm. The silver nanowires have a length of 15~25μm and a diameter of 20~40nm; The SERS substrate is a three-dimensional silver nanowire network structure.

2. The method for preparing a SERS substrate according to claim 1, characterized in that, The process of preparing the composite silver nanowire-gold nanoparticle SERS substrate in step (3) includes the following steps: (31) The silver nanowire sol was dropped onto a glass slide and heated in an oven to obtain a glass slide with silver nanowires; (32) Place the glass slide with silver nanowires obtained in step (31) on a hot plate and drop gold nanoparticle sol onto the glass slide with silver nanowires.

3. The method for preparing a SERS substrate according to claim 2, characterized in that, Step (32) The gold nanoparticle sol is added to the glass slide with silver nanowires in multiple drops, with the number of drops being 1 to 10.

4. The method for preparing a SERS substrate according to claim 3, characterized in that, Step (32): The amount of gold nanoparticle sol added to the glass slide with silver nanowires is 30~40 μl / cm² per unit area each time. 2 The concentration of gold nanoparticle sol was 0.5~1.2 mg / ml.

5. The method for preparing a SERS substrate according to claim 2, characterized in that, In step (31), the amount of silver nanowire sol added per unit area on the glass slide is 20~80 μl / cm. 2 The concentration of the silver nanowire sol was 0.5~1.5 mg / ml.

6. The method for preparing a SERS substrate according to claim 1, characterized in that, The process of preparing silver nanowire sol in step (1) includes the following steps: (11): Dissolve polyvinylpyrrolidone (PVP) in ethanol and stir to form a clear solution; (12): Add silver nitrate AgNO3 to the clear solution of step (11), seal the reaction, centrifuge and wash to obtain silver nanowire sol.

7. The method for preparing a SERS substrate according to claim 6, characterized in that, In step (12), the weight ratio of silver nitrate AgNO3 to PVP in step (11) is 1:15 to 1:

20.

8. The method for preparing a SERS substrate according to claim 6, characterized in that, The sealing reaction temperature in step (12) is 140~170℃, and the reaction time is 4~8h.

9. The method for preparing a SERS substrate according to claim 1, characterized in that, The gold nanoparticle sol is a gold nanorod sol, and its preparation process includes the following steps: (21): Prepare a seed solution containing HAuCl4, hexadecyltrimethylammonium bromide (CTAB) and NaBH4, wherein the molar ratio of HAuCl4, CTAB and NaBH4 in the seed solution is 1:380~400:2~3; (22): Prepare a growth solution containing HAuCl4, AgNO3, CTAB and ascorbic acid, wherein the molar ratio of HAuCl4, AgNO3, CTAB and ascorbic acid is 5:1~2:900~1100:7~12; (23): Add the seed solution prepared in step (21) to the growth solution in step (22), mix, let stand, centrifuge, and obtain gold nanorod sol.

10. A SERS substrate with a silver nanowire-gold nanoparticle composite structure prepared by any one of claims 1 to 9.

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