Silver nanowire-graphene-gold nanosphere composite sers substrate and method for preparing the same

Abstract

The application provides a silver nanowire-graphene-gold nanosphere composite SERS substrate and a preparation method thereof, and belongs to the technical field of organic contaminant detection. The substrate comprises a substrate, a silver nanowire layer coated on the substrate, and a gold nanosphere layer located at the uppermost layer; wherein a graphene film and mercaptan are coated between the silver nanowire layer and the gold nanosphere layer; the coverage of the silver nanowire layer on the substrate is 60%-80%; and the adhesion rate of the gold nanosphere layer to the graphene film is 50%-70%. In the SERS substrate provided by the application, graphene and mercaptan are added, PAHs in a solution are synergistically adsorbed through π-π stacking and hydrophobic effects, and polycyclic aromatic hydrocarbon molecules are effectively adsorbed to the surface of the SERS substrate, so that the detection effect of the polycyclic aromatic hydrocarbon molecules is further improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of organic pollutant detection, in particular to a silver nanowire-graphene-gold nanosphere composite SERS substrate and a preparation method of the silver nanowire-graphene-gold nanosphere composite SERS substrate. BACKGROUND

[0002] PAHs (Polycyclic Aromatic Hydrocarbons) are the products of incomplete combustion of fossil fuels or carbon-containing materials such as wood, tobacco, etc., and belong to a class of persistent organic pollutants. They have many characteristics such as a wide range of species, a wide distribution, a long degradation period, strong mutagenicity and carcinogenicity, and have brought great threats to the ecological environment and human health. Therefore, qualitative and quantitative detection of PAHs in the environment has high practical significance. In order to improve the detection convenience, get rid of the traditional processing steps which are complex and cumbersome and must be carried out under laboratory conditions, methods such as gas chromatography-mass spectrometry, fluorescence spectroscopy and electrochemistry are used. Now there is a method for detecting PAHs using SERS (Surface Enhanced Raman Spectroscopy) effect. SERS effect refers to the phenomenon that when light is incident, the Raman scattering signal of the adsorbed molecules is greatly enhanced due to the electromagnetic field enhancement of the nanostructure surface. As a new detection technology, SERS technology can overcome the low sensitivity of ordinary Raman spectroscopy, has the advantages of high sensitivity, rich chemical fingerprint information, simple operation, in-situ detection, etc., and is widely used in material, chemical, biological and medical detection and identification.

[0003] The core of detection using SERS effect is the construction of SERS substrate. In the SERS substrate, the nanometer gap between the nanostructures can form an electromagnetic field enhancement region. When the target molecules enter this region, their Raman signals can be effectively amplified. Only by adsorbing PAHs to the surface of the SERS substrate or even the nanometer gap, can the detection effect be effectively improved. Since PAHs are mostly benzene ring structures with few substituents, it is difficult to directly adsorb them to the substrate through covalent bonds, and more often through non-covalent bond forces. PAHs are hydrophobic and have many SP2 hybrid benzene rings, which can be adsorbed to the substrate surface through hydrophobic interaction and π-π stacking. The current SERS substrate needs to use large instruments such as etching machines and film coating machines, which is difficult to prepare and cannot guarantee that PAHs molecules are accurately adsorbed to the electromagnetic field enhancement region of the substrate, resulting in low monitoring accuracy. In view of the problems of the existing SERS substrate preparation difficulty and low detection accuracy, a new silver nanowire-graphene-gold nanosphere composite SERS substrate needs to be created. SUMMARY

[0004] The purpose of the embodiments of the present application is to provide a silver nanowire-graphene-gold nanosphere composite SERS substrate to at least solve the problems of difficult preparation and low detection accuracy of existing SERS substrates.

[0005] To achieve the above-mentioned purpose, the first aspect of the present application provides a silver nanowire-graphene-gold nanosphere composite SERS substrate, the substrate comprising: a substrate; a silver nanowire layer coated on the substrate; and a gold nanosphere layer located at the uppermost layer; wherein a graphene film and a mercaptan are coated between the silver nanowire layer and the gold nanosphere layer; the coverage of the silver nanowire layer on the substrate is 60%-80%; and the adhesion rate of the gold nanosphere layer to the graphene film is 50%-70%.

[0006] Optionally, the material of the substrate is glass.

[0007] Optionally, the silver nanowire layer is coated on the substrate in a three-dimensional network structure.

[0008] Optionally, the thickness of the graphene film is 2-10 nanometers.

[0009] The second aspect of the present application provides a preparation method of a silver nanowire-graphene-gold nanosphere composite SERS substrate, the method comprising: S1) synthesizing silver nanowire ethanol sol and gold nanosphere water sol, respectively; S2) dropping silver nanowire ethanol sol of a preset concentration onto a glass sheet at a preset temperature, and forming a three-dimensional silver nanowire network structure after the solution volatilizes; S3) coating graphene water solution of a preset concentration onto the surface of the silver nanowire network structure by using a spin coater, and forming a silver nanowire-graphene structure after the solution volatilizes; S4) placing the nanowire-graphene structure in a mercaptan solution of a preset concentration for a preset time, taking it out, and dropping polycyclic aromatic hydrocarbon ethanol solution onto the surface of the silver nanowire-graphene structure; S5) placing the silver nanowire-graphene structure on a hot plate of a preset temperature until the solution volatilizes; and S6) dropping gold nanosphere water sol of a preset concentration onto the surface of the silver nanowire-graphene structure, and forming a silver nanowire-graphene-gold nanosphere composite SERS substrate after the solution volatilizes.

[0010] Optionally, in step S1), the synthesis method of the silver nanowire ethanol sol is: stirring and mixing polyvinylpyrrolidone and deionized water, adding AgNO3, and stirring for 5-20 min; sealing the mixed liquid after stirring under the condition of 140-180℃ for 4-8 h; removing the suspension in the mixed liquid after placement, and centrifuging at 3000-5000 rpm for 3-10 min; repeating the steps of removing the suspension and centrifuging N times, and obtaining silver nanowire ethanol sol; wherein N≥3.

[0011] Optionally, in step S1), the synthesis method of the gold nanosphere hydrosol is: mixing HAuCl4 solution and deionized water to form a mixed solution under the condition of oil bath heating, after the mixed solution boils for 5-15 min, adding sodium citrate solution and keeping for 10-40 min; under the condition that the mixed solution becomes purple red, centrifuging at a speed of 2500-4500 rpm for 10-15 min to obtain the gold nanosphere hydrosol.

[0012] Optionally, in step S2), the preset temperature is 30-80℃.

[0013] Optionally, in step S2), the preset concentration of the silver nanowire ethanol mixed solution is 0.5-1.5 mg / ml.

[0014] Optionally, in step S2), the silver nanowire ethanol mixed solution of the preset concentration is added dropwise to the glass sheet, wherein the amount of the silver nanowire ethanol mixed solution is 5-20 ul.

[0015] Optionally, in step S3), the preset concentration of the graphene aqueous solution is 0.1-2.0 mg / ml.

[0016] Optionally, in step S3), the graphene aqueous solution of the preset concentration is coated to the surface of the silver nanowire network structure by using a spin coater, wherein the amount of the graphene aqueous solution is 5-20 ul.

[0017] Optionally, the graphene aqueous solution of the preset concentration is coated to the surface of the silver nanowire network structure by using a spin coater, wherein the rotation speed of the spin coater is 500-2000 r / min.

[0018] Optionally, in step S4), the nanowire-graphene structure is placed in a thiol solution of a preset concentration and soaked for a preset time, wherein the preset time is 10-90 min.

[0019] Optionally, in step S6), the gold nanosphere hydrosol of a preset concentration is added dropwise to the surface of the silver nanowire-graphene structure, wherein the dropwise environment temperature of the gold nanosphere hydrosol is 40-80℃; the preset concentration of the gold nanosphere hydrosol is 0.5-2.0 mg / ml; and the amount of the gold nanosphere hydrosol is 5-10 ul.

[0020] Through the technical scheme, the electric field is formed by the silver nanowires and the gold nanospheres, then a certain thickness is kept apart by the graphene film and the mercaptan, so that the PAHs molecules are adsorbed between the silver nanowires and the gold nanospheres, and are in the electromagnetic field enhancement region formed by the silver nanowires and the gold nanospheres, so that the number of target molecules entering the enhancement region is effectively increased, and the detection effect of the substrate is increased.

[0021] Other features and advantages of the present application will be illustrated in detail in the following detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0022] The accompanying drawings are included to provide a further understanding of the present application and are incorporated in and constitute a part of the specification, illustrate embodiments of the present application and serve to explain the principles of the present application, but are not intended to limit the present application. In the drawings:

[0023] Figure 1 is a structure schematic diagram of a silver nanowire-graphene-gold nanosphere composite SERS substrate provided by an embodiment of the present application;

[0024] Figure 2 is a step flow chart of a preparation method of a silver nanowire-graphene-gold nanosphere composite SERS substrate provided by an embodiment of the present application;

[0025] Figure 3 is a Raman signal diagram of pyrene under 10 -4 M different mercaptan modified SERS substrates provided by an embodiment of the present application;

[0026] Figure 4 is a Raman signal diagram of pyrene under 10 -4 M different concentrations of graphene provided by an embodiment of the present application;

[0027] Figure 5 is a Raman signal diagram of pyrene under different concentrations of corresponding SERS substrates provided by an embodiment of the present application;

[0028] Figure 6 is a relationship diagram of the concentration of pyrene and the Raman signal intensity provided by an embodiment of the present application.

[0029] REFERENCE NUMERALS

[0030] 10-substrate; 20-silver nanowire layer; 30-graphene film; 40-gold nanosphere layer; 50-mercaptan; 60-PAHs. DETAILED DESCRIPTION

[0031] The specific embodiments of the present application are described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and explanatory and are not intended to limit the present application.

[0032] Figure 1 is a structural diagram of a silver nanowire-graphene-gold nanosphere composite SERS substrate provided by an embodiment of the present application. As shown in Figure 1 the embodiment of the present application provides a silver nanowire-graphene-gold nanosphere composite SERS substrate, which comprises:

[0033] Preferably, the substrate 10 is made of glass.

[0034] Preferably, the silver nanowire layer 20 is in the form of a three-dimensional network structure on the substrate 10.

[0035] In the embodiment of the present application, the silver nanowire is in the form of a three-dimensional network structure, which facilitates subsequent graphene coating, increases the contact area between graphene and silver nanowires, thereby increasing the adhesion of graphene, avoids the peeling of the graphene layer during use, and improves the subsequent detection stability.

[0036] Preferably, the thickness of the graphene film 30 is 2-10 nanometers.

[0037] In the embodiment of the present application, the graphene film 30 has a thickness of 2-10 nanometers, so that there is a certain gap between the silver nanowire layer 20 and the gold nanosphere layer 40, which facilitates subsequent dropwise addition of PAHs 60, PAHs 60 are just added between silver nanowires and gold nanospheres, so that PAHs 60 are in a relatively strong electromagnetic field enhancement region, thereby improving the detection effect of the substrate.

[0038] Figure 2 is a method flow chart of a silver nanowire-graphene-gold nanosphere composite SERS substrate preparation method provided by an embodiment of the present application. As shown in Figure 2 the embodiment of the present application provides a silver nanowire-graphene-gold nanosphere composite SERS substrate preparation method, which comprises:

[0039] Step S10: Synthesize silver nanowire ethanol sol and gold nanosphere water sol, respectively.

[0040] Specifically, the silver nanowire-graphene-gold nanosphere composite SERS substrate provided by the present application needs a plurality of intermediate raw materials, which are obtained by a preliminary synthesis method, including silver nanowires and gold nanospheres. The synthesis method of the silver nanowires is as follows: polyvinylpyrrolidone is stirred and mixed with deionized water; AgNO3 is added and stirred vigorously for 5-20 min; the mixed solution is sealed at 140-180℃ for 4-8 h; the suspension in the mixed solution after standing is removed, and centrifuged at 3000-5000 rpm for 3-10 min; the suspension removal step and the centrifugation step are repeated at least three times to obtain silver nanowire ethanol sol.

[0041] Specifically, in one possible implementation, first, 0.1-0.5 g of polyvinylpyrrolidone (PVP, M W =55000) is added to 35 mL of deionized water, and after stirring for 10-50 min, a clear solution is formed. Then 0.01-0.03 g of AgNO3 is added, and the mixture is stirred vigorously for 5-20 min, and then transferred to a hydrothermal kettle (volume 50 mL) and sealed at 140-180℃ for 4-8 h. After the reaction, the suspension is removed and centrifuged at 3000-5000 rpm for 3-10 min, and repeated three times to obtain silver nanowire ethanol sol with a diameter of 15-25 nm and a length of 10-30 um.

[0042] Specifically, the synthesis method of the gold nanospheres is as follows: the HAuCl4 solution and deionized water are mixed under oil bath heating; after the mixed solution boils for 5-15 min, sodium citrate solution is added and kept for 10-40 min; when the mixed solution turns purple red, centrifugation is performed at a speed of 2500-4500 rpm for 10-15 min to obtain an aqueous solution of gold nanospheres. In one possible implementation, HAuCl4 solution (0.02 M, 0.1-0.5 mL) and 150 mL of deionized water are placed in a 250 mL single-neck flask, and the single-neck flask is heated in an oil bath until the solution in the single-neck flask boils, and after 5-15 min, 1-4 mL of 0.02 M sodium citrate solution is added, and the reaction is carried out for 10-40 min, and the solution slowly turns purple red. The reaction solution is centrifuged at 2500-4500 rpm for 10-15 min to obtain an aqueous sol of gold nanospheres with a diameter of 15-30 nm.

[0043] Step S20: The silver nanowire ethanol sol of a predetermined concentration is added dropwise to the glass sheet at a predetermined temperature, and a three-dimensional silver nanowire network structure is formed after the solution volatilizes.

[0044] Specifically, the glass slide was cleaned with piranha solution (a mixture of concentrated sulfuric acid and 30% hydrogen peroxide in a 7:3 volume ratio), then washed with acetone, ethanol, and deionized water, and finally dried with nitrogen gas. After obtaining a clean glass slide, it was placed in an oven at 30-80°C. 5-20 μL of a 0.5-1.5 mg / mL silver nanowire ethanol sol was dropped onto the glass slide. As the ethanol gradually evaporated, the silver nanowires self-assembled under capillary forces to form a silver nanowire network structure. The coverage of the glass substrate by these silver nanowires was 60%-80%.

[0045] Step S30: A graphene aqueous solution of a preset concentration is coated onto the surface of the silver nanowire network structure using a spin coater. After the solution evaporates, a silver nanowire-graphene structure is formed.

[0046] Specifically, a silver nanowire network structure is placed on a spin coater, and 5-20 μL of a 0.1-2.0 mg / mL graphene aqueous solution is added. The spin coater is operated at 500-2000 rpm for 30-90 seconds. After the solvent has completely evaporated, a silver nanowire-graphene composite structure is obtained. Under spin-coating conditions, the graphene solution can be uniformly dispersed on the substrate, thereby coating the silver nanowires with a uniformly dispersed 2-10 nm graphene film 30. This forms the silver nanowire-graphene structure.

[0047] Step S40: After immersing the nanowire-graphene structure in a thiol solution of a preset concentration for a preset time, remove it and drop a polycyclic aromatic hydrocarbon ethanol solution onto the surface of the silver nanowire-graphene structure.

[0048] Specifically, the obtained silver nanowire-graphene composite structure was placed in a solution with a concentration of 10... -1 M, 10 -2 M, 10 -3 Immerse the substrate in an ethanol solution of propanethiol, hexanethiol, and dodecyl mercaptan for 0.5–3 hours. The hydrophobic alkyl chains of the mercaptan will coat the substrate surface, forming a hydrophobic molecular layer. This layer adsorbs hydrophobic polycyclic aromatic hydrocarbons in the solution through van der Waals forces, thus enhancing the detection effect.

[0049] Step S50: Place the silver nanowire-graphene structure on a hot plate at a preset temperature until the solution evaporates.

[0050] Step S60: Drop gold nanosphere hydrosol of a preset concentration onto the surface of the silver nanowire-graphene structure. After the solution evaporates, a composite SERS substrate of silver nanowire-graphene-gold nanospheres is formed.

[0051] Specifically, 5-10 μL of 0.5-2.0 mg / mL gold nanosphere hydrosol was added. After the solution evaporated, the adhesion rate of the gold nanospheres on the graphene film 30 was 50%-70%.

[0052] The composite SERS substrate of silver nanowires-graphene-gold nanospheres generated by the present invention enables qualitative and quantitative detection of pyrene in polycyclic aromatic hydrocarbons. In one possible embodiment, 5-20 μL of 10 -2 M, 10 -3 M, 10 - 4 M, 10 -5 M, 10 -6 M, 10 -7 M, 10 -8 An ethanol solution of M-pyrene was dropped onto a SERS substrate and then tested under 785nm laser irradiation. Since different molecules exhibit different Raman characteristic peaks, the molecule type can be easily and quickly determined based on the position of the Raman peak, enabling qualitative detection of the target molecule. Furthermore, because the intensity of the Raman characteristic peak of a molecule has a quantitative relationship with its concentration, by combining the known peak intensity with an appropriate mathematical formula for fitting, a functional relationship between the target molecule concentration and the characteristic peak intensity can be obtained, thus achieving quantitative detection.

[0053] Example 1:

[0054] 1. First, add 0.3g of polyvinylpyrrolidone (PVP, M) W =55000) was added to 35 mL of deionized water, and stirred for 30 minutes to form a clear solution. Then, 0.017 g 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 suspension was removed and centrifuged at 4000 rpm for 5 minutes. This process was repeated three times to obtain an ethanol sol of silver nanowires with a diameter of 20 nm and a length of 20 μm.

[0055] 2. Next, 0.25 mL of HAuCl4 solution (0.02 M) and 150 mL of deionized water were placed in a 250 mL single-necked flask and heated in an oil bath until the solution in the flask boiled. After heating for 10 min, 2 mL of 0.02 M sodium citrate solution was added, and the reaction was allowed to proceed for 30 min, at which point the solution slowly turned purple-red. The reaction solution was centrifuged at 3500 rpm for 13 min to obtain a hydrosol of gold nanospheres with a diameter of 25 nm.

[0056] 3. The glass slide was then cleaned with piranha solution, followed by acetone, ethanol, and deionized water. Finally, it was dried with nitrogen to obtain a clean glass slide. The treated glass slide was then placed in a 50°C oven. 10 μL of a 1.0 mg / mL silver nanowire ethanol sol was dropped onto the glass slide. A three-dimensional silver nanowire network structure was obtained through solution evaporation and self-assembly, with the silver nanowires covering 70%-80% of the glass substrate.

[0057] 4. Continue immersing the silver nanowire structure in 10... -2 The silver nanowire structure was removed after immersing the substrate in an ethanol solution of hexamethylenetetramine (M) for 1 hour. The remaining hexamethylenetetramine solution was then removed using filter paper. The substrate was then rinsed three times in the ethanol solution to remove any residual hexamethylenetetramine from its surface. Finally, a hydrophobic thin film was formed on the surface of the silver nanowires.

[0058] 5. Add 5ul, 10 -4 An ethanol solution of M's pyrene was added dropwise to the substrate from step 4. After the solution had evaporated, the substrate was placed on a hot plate at 50°C, and 8 μL of an aqueous solution of 1.5 mg / mL gold nanospheres was added dropwise. After the solution had evaporated completely, a composite structure of silver nanowires and gold nanospheres was formed.

[0059] 6. The substrate was tested using a Horiba Xplus microconfocal Raman spectrometer. A 785nm laser with a power of 10mW was selected, the filter transmittance was set to 1%, the integration time was 20s, and the integration was performed twice. The Raman signal is as follows: Figure 3 As shown. The pyrene molecule at 590 cm⁻¹ -1 For example, when modified with hexamethylenetetramine, the strength is 4188.

[0060] Comparative Example 1:

[0061] The preparation steps are the same as in Example 1, except that hexamethylenetetramine in step 4 is replaced with dodecathiol. In this case, the Raman signal of the pyrene molecule is as follows: Figure 3 As shown, 590cm -1 The intensity at that location is 3151. The decrease in Raman intensity of pyrene molecules is mainly due to the excessively long carbon chain of dodecyl mercaptan, which leads to an excessively large spacing between the silver nanowires and gold nanospheres, resulting in a relatively low electromagnetic field intensity. Although the number of adsorbed target molecules increases, the overall Raman intensity still decreases.

[0062] Comparative Example 2:

[0063] The preparation steps are the same as in Example 1, except that hexamethylenetetramine in step 4 is replaced with propanethiol. In this case, the Raman signal of the pyrene molecule is as follows: Figure 3 As shown, 590cm -1The intensity at that location is 1211. The decrease in Raman intensity of the pyrene molecule is mainly due to the short carbon chain of propanethiol, resulting in too few adsorbed target molecules and thus a decrease in overall Raman intensity. From the three experiments above, it can be seen that hexanethiol is the most effective thiol.

[0064] Example 2:

[0065] 1. First, add 0.3g of polyvinylpyrrolidone (PVP, M) W =55000) was added to 35 mL of deionized water, and stirred for 30 minutes to form a clear solution. Then, 0.017 g 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 suspension was removed and centrifuged at 4000 rpm for 5 minutes. This process was repeated three times to obtain an ethanol sol of silver nanowires with a diameter of 20 nm and a length of 20 μm.

[0066] 2. Next, 0.25 mL of HAuCl4 solution (0.02 M) and 150 mL of deionized water were placed in a 250 mL single-necked flask and heated in an oil bath until the solution in the flask boiled. After heating for 10 min, 2 mL of 0.02 M sodium citrate solution was added, and the reaction was allowed to proceed for 30 min, at which point the solution slowly turned purple-red. The reaction solution was centrifuged at 3500 rpm for 13 min to obtain a hydrosol of gold nanospheres with a diameter of 25 nm.

[0067] 3. The glass slide was then cleaned with piranha solution, followed by acetone, ethanol, and deionized water. Finally, it was dried with nitrogen to obtain a clean glass slide. The treated glass slide was then placed in a 50°C oven. 10 μL of a 1.0 mg / mL silver nanowire ethanol sol was dropped onto the glass slide. A three-dimensional silver nanowire network structure was obtained through solution evaporation and self-assembly, with the silver nanowires covering 70%-80% of the glass substrate.

[0068] 4. Place the silver nanowire network structure from step 3 onto a spin coater, add 10 μL of a 0.25 mg / mL graphene aqueous solution, spin at 1000 rpm for 60 seconds. After the solution has evaporated, the silver nanowire-graphene structure is obtained.

[0069] 5. Immerse the silver nanowire-graphene structure from step 4 in 10... -2 The substrate was immersed in an ethanol solution of hexamethylenetetramine for 1 hour. Afterward, the structure was removed, and any remaining hexamethylenetetramine solution was absorbed with filter paper. The substrate was then washed three times in ethanol solution to remove any residual hexamethylenetetramine from the substrate surface. Further, 5 μL of ethanol was added to a 10 μL solution... -4An ethanol solution of M's pyrene was added dropwise to the above substrate. After the solution had evaporated completely, the substrate was placed on a hot plate at 50°C, and 8 μL of a 1.5 mg / mL gold nanosphere hydrosol was added dropwise. After the solution had evaporated completely, a composite structure of silver nanowires-graphene-gold nanospheres was formed.

[0070] 6. The substrate was tested using a Horiba Xplus microconfocal Raman spectrometer. A 785nm laser with a power of 10mW was selected, the filter transmittance was set to 1%, the integration time was 20s, and the integration was performed twice. The Raman signal is as follows: Figure 4 As shown. The pyrene molecule at 590 cm⁻¹ -1 For example, the strength at the location is 9800. The addition of graphene improves the adsorption capacity of the substrate for pyrene molecules (π-π stacking effect), and more molecules enter the gap between the silver nanowires and gold nanospheres, resulting in a significant enhancement compared to the strength (4188) in Example 1.

[0071] Comparative Example 3:

[0072] The preparation steps are the same as in Example 2, except that the concentration of the graphene aqueous solution during spin coating in step 4 is 0.5 mg / ml. At this time, the Raman signal intensity of the pyrene molecules is as follows: Figure 4 As shown. The pyrene molecule at 590 cm⁻¹ -1 Taking the intensity at a certain point as an example, the intensity is 15103. As the concentration of the graphene aqueous solution increases, the thickness of the graphene in the structure increases, and the adsorption capacity for pyrene molecules increases, thus further enhancing the signal.

[0073] Comparative Example 4:

[0074] The preparation steps are the same as in Example 4, except that the concentration of the graphene aqueous solution during spin coating in step 4 is 1.0 mg / ml. At this time, the Raman signal intensity of the pyrene molecules is as follows: Figure 4 As shown. The pyrene molecule at 590 cm⁻¹ -1 Taking the intensity at a certain point as an example, the intensity is 12579. Further increasing the concentration of the graphene aqueous solution increases the thickness of the graphene in the structure. Although this improves the adsorption capacity for pyrene molecules, the increased thickness leads to a larger gap between the silver nanowires and gold nanospheres, resulting in a decrease in electromagnetic field strength and thus a slight reduction in signal intensity.

[0075] Comparative Example 5:

[0076] The preparation steps are the same as in Example 2, except that the concentration of the graphene aqueous solution during spin coating in step 4 is 1.5 mg / ml. At this time, the Raman signal intensity of the pyrene molecules is as follows: Figure 4 As shown. The pyrene molecule at 590 cm⁻¹ -1Taking the intensity at a certain point as an example, the intensity is 7455. As the concentration of the graphene aqueous solution continues to increase, the thickness of the graphene in the structure further increases, leading to a further increase in the spacing between the silver nanowires and gold nanospheres, and a further decrease in the electromagnetic field intensity, thus resulting in a significant reduction in signal intensity.

[0077] Comparative Example 6:

[0078] The substrate preparation steps are the same as in Comparative Example 3, except that different concentrations (10) are used in step 5. -8 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 The Raman signal diagram of the solution of pyrene molecules (M) is shown in the attached figure. Figure 5 As shown in the figure, the characteristic peaks of pyrene molecules are mainly at 401, 590, 1058, 1235, 1403, and 1623 cm⁻¹. -1 The intensity of the characteristic peaks shows that as the concentration gradually decreases, the intensity of the characteristic peaks also gradually decreases, indicating that this SERS substrate can achieve a concentration of 10... -8 Qualitative detection of pyrene molecules at a concentration of M.

[0079] Furthermore, in order to achieve quantitative detection of pyrene molecules, according to the attached... Figure 5 The data in the image were used, with the intensity of the characteristic peak at 590 cm⁻¹ as the ordinate and the logarithm of the concentration as the abscissa, to obtain the attached... Figure 6 From the appendix Figure 6 It can be seen that the intensity of this characteristic peak exhibits a good functional relationship with the logarithm of its concentration. Based on this mathematical relationship, the intensity of the peak at 590 cm⁻¹ was measured. -1 After determining the intensity of the characteristic peak, the concentration of the solution can be calculated, thereby enabling the quantitative detection of pyrene molecules.

[0080] Those skilled in the art will understand that all or part of the steps in the methods of the above embodiments can be implemented by a program instructing related hardware. This program is stored in a storage medium and includes several instructions to cause a microcontroller, chip, or processor to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as a USB flash drive, a portable hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0081] The optional embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the embodiments of the present invention are not limited to the specific details described above. Within the scope of the technical concept of the embodiments of the present invention, various simple modifications can be made to the technical solutions of the embodiments of the present invention, and these simple modifications all fall within the protection scope of the embodiments of the present invention. It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the embodiments of the present invention will not further describe the various possible combinations.

[0082] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the embodiments of the present invention, they should also be regarded as the content disclosed by the embodiments of the present invention.

Claims

1. A composite SERS substrate of silver nanowires-graphene-gold nanospheres, characterized in that, The substrate includes: substrate; A silver nanowire layer coated on the substrate; and The topmost layer is gold nanospheres; In this configuration, a graphene film and a thiol are coated between the silver nanowire layer and the gold nanosphere layer from bottom to top. The hydrophobic alkyl long chains of thiols will cover the substrate surface, forming a hydrophobic molecular layer, which is used to adsorb hydrophobic polycyclic aromatic hydrocarbons in solution by van der Waals forces. The silver nanowire layer has a coverage of 60%-80% on the substrate; The adhesion rate of the gold nanosphere layer to the graphene film is 50%-70%.

2. The substrate according to claim 1, characterized in that, The substrate is made of glass.

3. The substrate according to claim 1, characterized in that, The silver nanowire layer is coated on the substrate in a three-dimensional mesh structure.

4. The substrate according to claim 1, characterized in that, The thickness of the graphene film is 2-10 nanometers.

5. A method for preparing a composite SERS substrate of silver nanowires-graphene-gold nanospheres, characterized in that, The method is used to fabricate a composite SERS substrate of silver nanowires-graphene-gold nanospheres as described in any one of claims 1-4, the method comprising: S1) synthesize silver nanowire ethanol sol and gold nanosphere hydrosol respectively; S2) At a preset temperature, a silver nanowire ethanol sol of a preset concentration is dropped onto a glass slide. After the solution evaporates, a three-dimensional silver nanowire network structure is formed. S3) A graphene aqueous solution of a preset concentration is coated onto the surface of the silver nanowire network structure using a spin coater. After the solution evaporates, a silver nanowire-graphene structure is formed. S4) After immersing the silver nanowire-graphene structure in a thiol solution of a preset concentration for a preset time, remove it and drop a polycyclic aromatic hydrocarbon ethanol solution onto the surface of the silver nanowire-graphene structure. S5) Place the silver nanowire-graphene structure on a hot plate at a preset temperature until the solution evaporates; S6) A gold nanosphere hydrosol of a preset concentration is dropped onto the surface of a silver nanowire-graphene structure. After the solution evaporates, a composite SERS substrate of silver nanowire-graphene-gold nanospheres is formed.

6. The method according to claim 5, characterized in that, In step S1), the method for synthesizing the silver nanowire ethanol sol is as follows: After mixing polyvinylpyrrolidone with deionized water, add AgNO3 and stir for 5-20 minutes. The stirred mixture should be sealed and left to stand at 140-180℃ for 4-8 hours; Remove the suspension from the mixture after standing, and centrifuge at 3000-5000 rpm for 3-10 min; Repeat the suspension removal and centrifugation steps N times to obtain silver nanowire ethanol sol; where N≥3.

7. The method according to claim 5, characterized in that, In step S1), the synthesis method of the gold nanosphere hydrosol is as follows: Under oil bath heating conditions, HAuCl4 solution and deionized water are mixed to form a mixture. After the mixture boils for 5-15 minutes, sodium citrate solution is added and kept for 10-40 minutes. When the mixture turns purple-red, centrifuge at 2500-4500 rpm for 10-15 min to obtain gold nanosphere hydrosol.

8. The method according to claim 5, characterized in that, In step S2), the preset temperature is 30-80℃.

9. The method according to claim 5, characterized in that, In step S2), the preset concentration of the silver nanowire ethanol sol is: 0.5-1.5 mg / ml.

10. The method according to claim 5, characterized in that, In step S2), the silver nanowire ethanol mixture of a preset concentration is dropped onto a glass slide, wherein the amount of the silver nanowire ethanol mixture is 5-20 μL.

11. The method according to claim 5, characterized in that, In step S3), the preset concentration of the graphene aqueous solution is: 0.1-2.0 mg / ml.

12. The method according to claim 5, characterized in that, In step S3), a graphene aqueous solution of a preset concentration is coated onto the surface of the silver nanowire mesh structure using a spin coater, wherein the amount of the graphene aqueous solution is 5-20 μL.

13. The method according to claim 5, characterized in that, In step S3), a graphene aqueous solution of a preset concentration is coated onto the surface of the silver nanowire mesh structure using a spin coater, wherein the rotation speed of the spin coater is 500-2000 r / min.

14. The method according to claim 5, characterized in that, In step S4), the silver nanowire-graphene structure is immersed in a thiol solution of a preset concentration for a preset time, wherein the preset time is 10-90 min.

15. The method according to claim 5, characterized in that, In step S6), the gold nanosphere hydrosol of a preset concentration is dropped onto the surface of the silver nanowire-graphene structure, wherein... The dropwise addition temperature of the gold nanosphere hydrosol is 40-80℃; The preset concentration of the gold nanosphere hydrosol is 0.5-2.0 mg / ml; The amount of the gold nanosphere hydrosol used is 5-10 μL.

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