An in-situ preparation method of a flexible SERS substrate based on a nano-film

Abstract

The present invention discloses an in-situ preparation method of a flexible SERS substrate based on a nano-film. First, a self-supporting nano-film is prepared through gas-liquid interface assembly and condensation reaction. After the prepared nano-film is supported by a nylon washer or a PC nuclear pore membrane, it is fixed in the middle of an H-type electrolytic cell. Subsequently, two reactant solutions are respectively added to both sides of the H-type electrolytic cell. The reactant with a fast diffusion rate preferentially passes through the nano-film, contacts with the other reactant and reacts, and uniformly distributed nano-particles are in-situ generated on the nano-film, thereby obtaining the SERS substrate. By changing the number of reaction times, the present invention can regulate the particle size and particle gap of the nano-particles on the SERS substrate, and can prepare a large-area uniform flexible SERS substrate. The SERS substrate prepared by the present invention has the advantages of no background signal, high sensitivity, high enhancement factor, repeatable preparation, and stable signal.

Description

Technical Field

[0001] The present invention belongs to the technical field of SERS substrate preparation, and particularly relates to an in-situ preparation method of a flexible SERS substrate based on a nano-film. Background Art

[0002] Surface-enhanced Raman scattering (SERS) is a detection technology with outstanding advantages such as non-destructive, high sensitivity, and fingerprint recognition. Currently, it has been widely used in fields such as energy science, medical diagnosis, food safety, and environmental monitoring. The SERS detection performance highly depends on the SERS substrate used. Therefore, developing SERS substrates with good uniformity, high sensitivity, and good repeatability is the key to improving the SERS detection ability.

[0003] Currently, most studies are still based on rigid SERS substrates, such as silicon wafers, glass, metal sheets, etc. These can only use indirect sampling methods such as drop coating and soaking, and it is difficult to meet the detection requirements of complex samples in daily life. Therefore, it greatly limits the practical application of SERS technology. The SERS substrate prepared with a flexible transparent support material can well adhere to the surfaces of various-shaped objects to achieve in-situ detection. Currently, the reported flexible transparent SERS substrates mostly use polymers such as PDMS, PMMA, tapes, etc. as support materials. A method of preparing active metal materials on the support material through thermal deposition or electron beam deposition technology can obtain a highly uniform and reproducible SERS substrate. However, this method also faces problems such as high preparation cost and difficulty in large-scale preparation. In addition, a simple and efficient method is to prepare a colloidal solution of nanoparticles in advance and then adsorb / embed it into the support material. However, it has disadvantages such as poor uniformity and reproducibility of the prepared SERS substrate. There are also literature reports on SERS substrates prepared by in-situ reduction methods, but there are problems of poor uniformity. In addition, polymer films mostly have strong background signals, making it difficult to improve the signal-to-noise ratio. Moreover, the thickness of conventional polymer films is often in the micron level or even thicker, which significantly affects the Raman signal collection efficiency during in-situ detection. These are not conducive to improving the SERS detection performance. Therefore, there is an urgent need to develop a preparation method for flexible transparent SERS substrates with high sensitivity, large enhancement factor, good uniformity, and capable of large-area preparation. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above-mentioned existing technical problems, and provide an in-situ preparation method of a flexible SERS substrate based on a nano-film. The SERS substrate prepared by this method has the advantages of no background signal, high sensitivity, high enhancement factor, reproducible preparation, stable signal, etc., and can achieve the preparation of a large-area and uniform flexible SERS substrate.

[0005] To achieve the above purpose, the technical solution adopted by the present invention includes the following steps:

[0006] (1) Preparation of self - supporting nanofilms

[0007] Add the hydrazide - based compound or amino - based compound and aldehyde - based compound into dimethyl sulfoxide. After heating until the solid phase is completely dissolved, let the solution stand at room temperature to obtain the precursor solution. Drop the precursor solution onto the hydrophilically treated glass substrate, and then under the induction conditions of room temperature and humidity greater than 60%, carry out the Schiff - base condensation reaction for 4 - 10 hours to form a nanofilm at the gas - liquid interface, and obtain the self - supporting nanofilm through washing treatment.

[0008] (2) Preparation of flexible SERS substrates using self - supporting nanofilms as templates

[0009] Use a nylon washer or a PC nuclear pore membrane to pick up the self - supporting nanofilm and let it dry. Then fix it in the middle of an H - type electrolytic cell, and add the two reactant solutions required for preparing the SERS substrate to both sides of the H - type electrolytic cell respectively. After the reaction is complete at room temperature, remove the solutions on both sides, wash with deionized water and dry, then remove the nylon washer or dissolve the PC nuclear pore membrane with dichloromethane to obtain a flexible SERS substrate containing noble metal or semiconductor nanomaterials.

[0010] In the above step (1), the selected hydrazide - based compound or amino - based compound and aldehyde - based compound should be able to undergo Schiff - base condensation reaction to form a self - supporting nanofilm. Preferably, the hydrazide - based compound is any one of calix[4]pyrrole tetra - hydrazide, calix[4]arene tetra - hydrazide, pillar[5]arene di - hydrazide, trimesoyl hydrazide, etc., the amino - based compound is any one of 4,4'-diaminodiphenyl ether, 1,3,5 - triaminobenzene, 4,4’4”-triaminotriphenylamine, tetrakis(4 - aminophenyl)methane, etc., and the aldehyde - based compound is any one of trimesic aldehyde, tris(4 - formylphenyl)amine, tris(4 - formylphenyl)benzene, tetrakis(4 - benzaldehydephenyl)methane.

[0011]

[0012]

[0013] Further, in the above step (2), add an aqueous solution of NaBH 4 and an aqueous solution of AgNO 3 containing sodium citrate or an aqueous solution of HAuCl 4 as the reactant solutions to both sides of the H - type electrolytic cell respectively. The aqueous solution of NaBH 4 is added to one side of the nanofilm, and the aqueous solution of AgNO 3 or the aqueous solution of HAuCl 4 is added to the other side. React at room temperature for 6 - 10 hours to obtain a silver nanoparticle / nanofilm SERS substrate or a gold nanoparticle / nanofilm SERS substrate accordingly.

[0014] Further, in the above step (2), an aqueous solution of Cd(NO 3 ) 2 or ZnCl 2 containing polyvinylpyrrolidone and an aqueous solution of thioacetamide are added to both sides of the H-type electrolytic cell as reactant solutions. Among them, the aqueous solution of Cd(NO 3 ) 2 or the aqueous solution of ZnCl 2 is added to one side of the nanofilm, and the aqueous solution of thioacetamide is added to the other side. The reaction is carried out at room temperature for 9 to 12 hours, and a cadmium sulfide nanoparticle / nanofilm SERS substrate or a zinc sulfide nanoparticle / nanofilm SERS substrate is obtained accordingly.

[0015] Further, in the above step (2), first, an aqueous solution of Cd(NO 3 ) 2 containing polyvinylpyrrolidone and an aqueous solution of thioacetamide are added to both sides of the H-type electrolytic cell as reactant solutions. Among them, the aqueous solution of Cd(NO 3 ) 2 is added to one side of the nanofilm, and the aqueous solution of thioacetamide is added to the other side. The reaction is carried out at room temperature for 9 to 12 hours to uniformly grow cadmium sulfide nanoparticles on one side of the nanofilm. Then, an aqueous solution of NaBH 4 and an aqueous solution of AgNO 3 containing sodium citrate are added to both sides of the H-type electrolytic cell as reactant solutions. Among them, the aqueous solution of NaBH 4 is added to the side of the nanofilm where cadmium sulfide nanoparticles are grown, and the aqueous solution of AgNO 3 is added to the other side. The reaction is carried out at room temperature for 6 to 10 hours to uniformly grow silver nanoparticles on one side of the nanofilm, and a silver / cadmium sulfide nanoparticle / nanofilm SERS substrate is obtained accordingly.

[0016] Preferably, the concentration of the above aqueous solution of NaBH 4 is 0.10 to 1.0 mmol / L, and the mass concentration of sodium citrate in the aqueous solution of AgNO 3 or HAuCl 4 is 0.10 wt% to 2.0 wt%, and the concentration of AgNO 3 or HAuCl 4 is 0.10 to 0.50 mmol / L.

[0017] Preferably, the mass concentration of polyvinylpyrrolidone in the above aqueous solution of Cd(NO 3 ) 2 or ZnCl 2 containing polyvinylpyrrolidone is 0.5 wt% to 3.0 wt%, and Cd(NO3 ) 2 or ZnCl 2 has a concentration of 0.01 to 0.1 mmol / L, and the aqueous thioacetamide solution has a concentration of 0.05 to 0.5 mmol / L.

[0018] In addition, in the above step (2), by replacing the fresh reactant solution and changing the number of reactions, the particle size and particle gap of the noble metal or semiconductor nanoparticles on the SERS substrate are regulated.

[0019] Compared with the prior art, the present invention has the following beneficial technical effects:

[0020] The SERS substrate of the present invention is prepared by using a porous, highly uniform and defect-free nanofilm as a template, and a layer of uniformly distributed metal and semiconductor nanoparticles is prepared on the nanofilm by an interfacial in-situ reduction method. The in-situ grown nanoparticles are all on one side of the nanofilm. When performing SERS testing, the nanoparticles within the laser region can all be excited, so the utilization rate of the nanoparticles prepared by this method is high. At the same time, this method can realize the preparation of a large-area flexible SERS substrate. The present invention can control the particle size and particle gap of the in-situ grown nanoparticles by controlling the reaction time and changing the number of times of replacing the reactant solution. The detection of rhodamine 6G by this SERS substrate shows that the substrate has advantages such as no background signal, high sensitivity, high enhancement factor, and good uniformity. At the same time, the obtained SERS substrate can realize the detection and identification of complex samples and the in-situ detection of pesticides. In addition, the method of the present invention is also applicable to the preparation of other morphologies of metal and semiconductor nanomaterials, and has universality. Description of the Drawings

[0021] Figure 1 are SEM images of both sides of the self-supporting cup [4] pyrrole nanofilm (a) and the silver nanoparticle / nanofilm SERS substrate (b) prepared in Example 1.

[0022] Figure 2 are SEM images of the silver nanoparticle / nanofilm SERS substrates with different growth times prepared in Example 1; among them, a to d are the silver nanoparticle / nanofilm SERS substrates with growth times of 1 to 4 in sequence.

[0023] Figure 3 is a photograph of the large-area silver nanoparticle / nanofilm / PC nuclear pore membrane SERS substrate prepared in Example 3.

[0024] Figure 4 are SEM images of the cadmium sulfide nanoparticle / nanofilm SERS substrate (a) prepared in Example 4 and the silver / cadmium sulfide nanoparticle / nanofilm SERS substrate (b) prepared in Example 5.

[0025] Figure 5 The SERS signals of rhodamine 6G by the 7 kinds of SERS substrates prepared in Examples 1, 2, and 3.

[0026] Figure 6 The uniformity test of the SERS substrate 3 prepared in Example 1.

[0027] Figure 7 The test of the SERS substrate 3 prepared in Example 1 for rhodamine 6G with different concentrations.

[0028] Figure 8 The test of the SERS substrate 3 prepared in Example 1 for fentanyl content with different concentrations in methanol and urine.

[0029] Figure 9 The in-situ detection of thiram pesticide on cherry tomatoes by the SERS substrate 3 prepared in Example 1. Detailed implementation manners

[0030] The present invention will be further described in detail below in conjunction with the drawings and examples, but the protection scope of the present invention is not limited to the following examples.

[0031] Example 1

[0032] 1. Preparation of self-supporting calix[4]pyrrole nanofilms

[0033] Dissolve 0.77 mg (1 mmol) of calix[4]pyrrole tetrahydrazide and 0.23 mg (1 mmol) of benzene-1,3,5-tricarbaldehyde in 200 μL of dimethyl sulfoxide. After heating until the solid phase is completely dissolved, let the solution stand to room temperature to obtain a precursor solution. Drop 70 μL of the precursor solution onto a 1.5 cm × 1.5 cm glass substrate cleaned by a plasma cleaner, and then carry out a Schiff base condensation reaction for 4 hours under the induction conditions of a temperature of 25 °C and a humidity of 60%. After the reaction, the nanofilm will grow on the surface of dimethyl sulfoxide on the glass substrate. Take out the glass substrate and soak it in secondary water. The nanofilm floats on the water surface, and the nanofilm is washed with secondary water to obtain a self-supporting calix[4]pyrrole nanofilm.

[0034] 2. Preparation of silver nanoparticle / nanofilm SERS substrates with different growth times

[0035] Use a nylon washer with a diameter of 7 mm to pick up and dry the self-supporting calix[4]pyrrole nanofilm prepared in step 1, and then fix it in the middle of a 1 cm diameter H-type electrolytic cell. Add 10 mL of 0.4 mmol / L NaBH 4 aqueous solution and 10 mL of 0.15 mmol / L AgNO 3 aqueous solution containing 0.15 wt% sodium citrate to both sides of the H-type electrolytic cell, where NaBH4 An aqueous solution is added to one side of the nanofilm, and AgNO 3 An aqueous solution is added to the other side. After reacting for 6 hours at room temperature, NaBH 4 A layer of silver nanoparticles grows on the nanofilm on the side of the aqueous solution, while no silver nanoparticles are formed on the other side of the nanofilm and in the solution in the container. The solutions on both sides of the H-type electrolytic cell are removed, washed with deionized water, dried, the nylon gaskets are removed, and a nanofilm with uniformly distributed silver nanoparticles is obtained, that is, a silver nanoparticle / nanofilm SERS substrate, denoted as SERS substrate 1. Then, the same amount of freshly prepared reaction solution is added to the containers on both sides of the electrolytic cell, and silver nanoparticles with a more compact distribution can be obtained on the nanofilm. By changing the number of times the reaction solution is replaced, nanofilms containing silver nanoparticles with different particle sizes and gaps can be obtained. In this example, according to the number of times the reaction solution is replaced, SERS substrate 1, SERS substrate 2, SERS substrate 3, and SERS substrate 4 are obtained in sequence, and their distribution is as shown in Figure 1 and Figure 2 shown.

[0036] Example 2

[0037] 1. Preparation of self-supporting calix[4]pyrrole nanofilm

[0038] The self-supporting calix[4]pyrrole nanofilm is prepared according to the method in step 1 of Example 1.

[0039] 2. Preparation of silver nanoparticle / nanofilm SERS substrate

[0040] The self-supporting calix[4]pyrrole nanofilm prepared in step 1 is fished up and dried using a PC nuclear pore membrane with a pore size of 0.2 μm and a thickness of 12 mm, and then fixed in the middle of a 1-cm-diameter H-type electrolytic cell. 10 mL of 0.4 mmol / L NaBH 4 aqueous solution and 10 mL of 0.15 mmol / L AgNO 3 aqueous solution containing 0.15 wt% sodium citrate are added to both sides of the H-type electrolytic cell. Among them, the NaBH 4 aqueous solution is added to one side of the nanofilm, and the AgNO 3 aqueous solution is added to one side of the PC nuclear pore membrane. After reacting for 6 hours at room temperature, NaBH 4A layer of silver nanoparticles grew on the nanofilm on the aqueous solution side, while no silver nanoparticles were formed on the other side of the nanofilm and in the solution in the container. Remove the solutions on both sides of the H-type electrolytic cell, repeat the above steps 2 times after washing with deionized water, and obtain a silver nanoparticle / nanofilm / PC nuclear pore membrane SERS substrate after drying, denoted as SERS substrate 5. Dissolve the PC nuclear pore membrane in the silver nanoparticle / nanofilm / PC nuclear pore membrane SERS substrate with dichloromethane, and the nanofilm and silver nanoparticles will not be damaged, obtaining a nanofilm with uniformly distributed silver nanoparticles, that is, a silver nanoparticle / nanofilm SERS substrate, denoted as SERS substrate 6.

[0041] Example 3

[0042] 1. Prepare a self-supporting calix[4]pyrrole nanofilm

[0043] Prepare a self-supporting calix[4]pyrrole nanofilm according to the method of step 1 in Example 1.

[0044] 2. Prepare a large-area silver nanoparticle / nanofilm SERS substrate

[0045] Use a PC nuclear pore membrane with a pore size of 0.2 μm and a thickness of 12 mm to lift and dry the calix[4]pyrrole nanofilm prepared in step 1, and then fix it in the middle of an H-type electrolytic cell with a diameter of 8 cm. Add 500 mL of 0.4 mmol / L NaBH 4 aqueous solution and 500 mL of 0.15 mmol / L AgNO 3 aqueous solution containing 0.15 wt% sodium citrate to both sides of the H-type electrolytic cell, where the NaBH 4 aqueous solution is added to one side of the nanofilm, and the AgNO 3 aqueous solution is added to one side of the PC nuclear pore membrane. After reacting at room temperature for 12 hours, a layer of uniformly distributed silver nanoparticles grew on the nanofilm on the side where the NaBH 4 aqueous solution was added, while no silver nanoparticles were formed on the other side of the nanofilm and in the solution in the container. Remove the solutions on both sides of the H-type electrolytic cell, repeat the above steps 2 times after washing with deionized water, and obtain a silver nanoparticle / nanofilm / PC nuclear pore membrane SERS substrate with an effective area of about 50 cm 2 as Figure 3 . Dissolve the PC nuclear pore membrane in the silver nanoparticle / nanofilm / PC nuclear pore membrane SERS substrate with dichloromethane, and the nanofilm and silver nanoparticles will not be damaged, obtaining a nanofilm with uniformly distributed silver nanoparticles, that is, a large-area silver nanoparticle / nanofilm SERS substrate, denoted as SERS substrate 7.

[0046] Example 4

[0047] 1. Preparation of self - supported calix[4]pyrrole nanofilms

[0048] Prepare self - supported calix[4]pyrrole nanofilms according to the method of step 1 in Example 1.

[0049] 2. Preparation of cadmium sulfide nanoparticle / nanofilm SERS substrates

[0050] Use a nylon washer with a diameter of 7 mm to lift the calix[4]pyrrole nanofilm prepared in step 1 and let it dry. Then fix it in the middle of a 1 - cm - diameter H - type electrolytic cell. Add 10 mL of 0.02 mmol / L Cd(NO 3 ) 2 aqueous solution containing 1 wt% polyvinylpyrrolidone and 10 mL of 0.1 mmol / L thioacetamide aqueous solution to both sides of the H - type electrolytic cell. The Cd(NO 3 ) 2 aqueous solution is added to one side of the nanofilm, and the thioacetamide aqueous solution is added to the other side. After reacting at room temperature for 9 hours, a layer of cadmium sulfide nanoparticles grows on the nanofilm on the side where the Cd(NO 3 ) 2 aqueous solution is added, while no cadmium sulfide nanoparticles are formed on the other side of the nanofilm and in the solution in the container. Remove the solutions on both sides of the H - type electrolytic cell, wash with deionized water, dry, remove the nylon washer, and obtain a nanofilm with uniformly distributed cadmium sulfide nanoparticles, that is, the cadmium sulfide nanoparticle / nanofilm SERS substrate, and its distribution is as shown in Figure 4 a.

[0051] Example 5

[0052] 1. Preparation of self - supported calix[4]pyrrole nanofilms

[0053] Prepare self - supported calix[4]pyrrole nanofilms according to the method of step 1 in Example 1.

[0054] 2. Preparation of silver / cadmium sulfide nanoparticle / nanofilm SERS substrates

[0055] First, prepare a cadmium sulfide nanoparticle / nanofilm SERS substrate according to the method of step 2 in Example 4. Then fix the cadmium sulfide nanoparticle / nanofilm SERS substrate in the middle of a 1 - cm - diameter H - type electrolytic cell. Add 10 mL of 0.4 mmol / L NaBH 4 aqueous solution and 10 mL of 0.15 mmol / L AgNO 3 aqueous solution containing 0.15 wt% sodium citrate to both sides of the H - type electrolytic cell. The NaBH 4 aqueous solution is added to the side of the cadmium sulfide nanoparticles, and the AgNO 3The aqueous solution was added to the other side. After reacting for 6 hours at room temperature, the solutions on both sides of the H-type electrolytic cell were removed. After washing with deionized water and drying, the nylon gaskets were removed to obtain the silver / cadmium sulfide nanoparticle / nanofilm SERS substrate, and its distribution is as shown in Figure 4 Figure b.

[0056] To prove the beneficial effects of the present invention, the inventors respectively carried out various performance tests on the SERS substrates prepared in the above examples, and the experiments are as follows:

[0057] 1. SERS test of rhodamine 6G on different SERS substrates

[0058] The 7 SERS substrates in Examples 1, 2, and 3 were respectively loaded on 4 mm×4 mm silicon wafers ultrasonically cleaned with ethanol, and then 10 μL of an aqueous solution of rhodamine 6G with a concentration of 1.0×10 -8 mol / L was added dropwise. After the solution had evaporated completely, the 7 SERS substrates were tested using an inVia Reflex type microconfocal Raman spectrometer developed by Renishaw Company, UK. The experimental parameters were set as follows: the laser wavelength was 532 nm, the laser power was 50 mW, and the exposure time was 10 s. The results are as shown in Figure 5 Figure. It can be seen from Figure 5 that the SERS substrate grown 3 times has the best enhancement effect; the PC nuclear pore membrane will weaken the enhancement effect of the SERS substrate; after removing the PC nuclear pore membrane, the enhancement effect of SERS returns to the best state; the SERS substrate can be prepared in an enlarged manner without loss of performance.

[0059] 2. Uniformity test of the SERS substrate

[0060] The SERS substrate 3 was loaded on a 4 mm×4 mm silicon wafer, and then 10 μL of an aqueous solution of rhodamine 6G with a concentration of 1.0×10 -8 mol / L was added dropwise. After the solution had evaporated completely, an inVia Reflex type microconfocal Raman spectrometer developed by Renishaw Company, UK was used to select 49 points for testing within an area of 14 μm×14 μm on the SERS substrate 3. The results are as shown in Figure 6 Figure. The results show that the SERS substrate has good uniformity (RSD = 12%).

[0061] 3. SERS test of rhodamine 6G at different concentrations

[0062] The SERS substrate 3 was loaded on a 4 mm×4 mm silicon wafer, and then 10 μL of different concentrations (1.0×10 -8 mol / L to 1.0×10 -15An aqueous solution of rhodamine 6G at a concentration of (mol / L). After the solution has completely evaporated, testing is carried out on the SERS substrate 3 using an inVia Reflex type microscopic confocal Raman spectrometer developed by Renishaw plc, UK. The results are as Figure 7 shown. The results indicate that the detection limit of this SERS substrate for rhodamine 6G can be as low as 1.0×10 -15 mol / L.

[0063] 4. SERS testing of fentanyl with different contents in methanol

[0064] Load the SERS substrate 3 onto a 4 mm × 4 mm silicon wafer, and then add 10 μL of fentanyl methanol solutions with different concentrations (1.0×10 -4 g / mL to 1.0×10 -8 g / mL). After the solution has completely evaporated, testing is carried out on the SERS substrate 3 using an inVia Reflex type microscopic confocal Raman spectrometer developed by Renishaw plc, UK. The results are as Figure 8 shown in Fig. a. The results indicate that the detection limit of this SERS substrate for pure fentanyl can be as low as 1.0×10 -8 g / mL.

[0065] 5. SERS testing of fentanyl with different contents in urine

[0066] Add fentanyl to urine that has been centrifuged and filtered using a nylon membrane to prepare fentanyl solutions with different concentrations (1.0×10 -4 g / mL to 1.0×10 -8 g / mL). Load the SERS substrate 3 onto a 4 mm × 4 mm silicon wafer, and then add 10 μL of fentanyl solutions with different concentrations. After the solution has completely evaporated, testing is carried out on the SERS substrate 3 using an inVia Reflex type microscopic confocal Raman spectrometer developed by Renishaw plc, UK. The results are as Figure 8 shown in Fig. b. The results indicate that the detection limit of this SERS substrate for fentanyl in urine can be as low as 1.0×10 -7 g / mL.

[0067] 6. In-situ detection of thiram pesticide on cherry tomatoes using the SERS substrate

[0068] Add 10 μL of an aqueous thiram solution with a concentration of 1.0×10 -7 M to a washed cherry tomato. After the solution has completely evaporated, attach the SERS substrate 3 to the position where thiram was added. Then, testing is carried out on the SERS substrate 3 using an inVia Reflex type microscopic confocal Raman spectrometer developed by Renishaw plc, UK. The results are as Figure 9As shown. The results show that the SERS substrate can detect thiram pesticide on cherry tomatoes (1.0×10 -7 M). In the above Examples 1 to 5, the calix[4]pyrrole tetraacylhydrazine used can also be replaced by any one of calix[4]arene tetraacylhydrazine, pillar[5]arene diacylhydrazine, trimellitic hydrazide, 4,4'-diaminodiphenyl ether, 1,3,5-triaminobenzene, 4,4’4”-triaminotriphenylamine, tetrakis(4-aminophenyl)methane, etc., and trimellitic tricarbaldehyde can also be replaced by any one of tris(4-formylphenyl)amine, tris(4-formylphenyl)benzene, tetrakis(4-benzaldehydyl)methane, etc. Schiff base condensation reactions can occur between these compounds to form self-supporting nanofilms, and these self-supporting nanofilms can all be used as templates. Accordingly, a layer of uniformly distributed metal and semiconductor nanoparticles can be prepared on the nanofilms by the method of interfacial in-situ reduction to realize the preparation of a large-area flexible SERS substrate.

Claims

1. A method for in-situ preparation of a flexible SERS substrate based on a nano-film, characterized in that, it comprises the following steps: (1) Preparation of a self-supporting nano-film Adding a hydrazide compound or an amino compound and an aldehyde compound into dimethyl sulfoxide, heating until the solid phase is completely dissolved, then allowing the solution to stand at room temperature to obtain a precursor solution; dropping the precursor solution onto a glass substrate after hydrophilic treatment, and then carrying out a Schiff base condensation reaction for 4 to 10 hours under induction conditions of room temperature and humidity greater than 60% to form a nano-film at the gas-liquid interface, and obtaining a self-supporting nano-film through washing treatment; (2) Preparation of a flexible SERS substrate using the self-supporting nano-film as a template Lifting the self-supporting nano-film with a nylon washer or a PC nuclear pore membrane and drying it, then fixing it in the middle of an H-shaped electrolytic cell, and adding two reactant solutions required for preparing the SERS substrate to both sides of the H-shaped electrolytic cell respectively. After the reaction is complete at room temperature, removing the solutions on both sides, washing with deionized water and drying, then removing the nylon washer or dissolving the PC nuclear pore membrane with dichloromethane to obtain a flexible SERS substrate containing noble metal or semiconductor nano-materials; In step (2), an aqueous solution of NaBH 4 and an aqueous solution of AgNO 3 containing sodium citrate or an aqueous solution of HAuCl 4 are added to both sides of the H-shaped electrolytic cell as reactant solutions. Among them, the aqueous solution of NaBH 4 is added to one side of the nanomembrane, and the aqueous solution of AgNO 3 or the aqueous solution of HAuCl 4 is added to the other side, and the reaction is carried out at room temperature for 6 to 10 hours to obtain a silver nanoparticle / nanomembrane SERS substrate or a gold nanoparticle / nanomembrane SERS substrate accordingly.

2. The method for in-situ preparation of a flexible SERS substrate based on a nano-film according to claim 1, characterized in that, in step (1), the hydrazide compound is any one of calix[4]pyrrole tetra-hydrazide, calix[4]arene tetra-hydrazide, pillar[5]arene di-hydrazide, and trimesoyl hydrazide; the amino compound is any one of 4,4'-diaminodiphenyl ether, 1,3,5-triaminobenzene, 4,4’4’’-triaminotriphenylamine, and tetrakis(4-aminophenyl)methane; the aldehyde compound is any one of trimesic aldehyde, tris(4-formylphenyl)amine, tris(4-formylphenyl)benzene, and tetrakis(4-benzaldehyde)methane.

3. The method for in-situ preparation of a flexible SERS substrate based on a nano-film according to claim 1, characterized in that, In step (2), an aqueous solution of Cd(NO 3 ) 2 or ZnCl 2 containing polyvinylpyrrolidone and an aqueous solution of thioacetamide are added to both sides of the H-shaped electrolytic cell as reactant solutions, where the aqueous solution of Cd(NO 3 ) 2 or the aqueous solution of ZnCl 2 is added to one side of the nanofilm, and the aqueous solution of thioacetamide is added to the other side, and the reaction is carried out at room temperature for 9 to 12 hours, and a cadmium sulfide nanoparticle / nanofilm SERS substrate or a zinc sulfide nanoparticle / nanofilm SERS substrate is correspondingly obtained.

4. The method for in-situ preparation of a flexible SERS substrate based on a nano-film according to claim 1, characterized in that, In step (2), an aqueous solution of Cd(NO 3 ) 2 containing polyvinylpyrrolidone and an aqueous solution of thioacetamide are respectively added to both sides of the H-shaped electrolytic cell as reactant solutions. Among them, the aqueous solution of Cd(NO 3 ) 2 is added to one side of the nanomembrane, and the aqueous solution of thioacetamide is added to the other side. The reaction is carried out at room temperature for 9 to 12 hours to uniformly grow cadmium sulfide nanoparticles on one side of the nanomembrane. Then, an aqueous solution of NaBH 4 and an aqueous solution of AgNO 3 containing sodium citrate are respectively added to both sides of the H-shaped electrolytic cell as reactant solutions. Among them, the aqueous solution of NaBH 4 is added to the side of the nanomembrane where cadmium sulfide nanoparticles are grown, and the aqueous solution of AgNO 3 is added to the other side. The reaction is carried out at room temperature for 6 to 10 hours to uniformly grow silver nanoparticles on one side of the nanomembrane again, and a silver / cadmium sulfide nanoparticle / nanomembrane SERS substrate is correspondingly obtained.

5. The method for in-situ preparation of a flexible SERS substrate based on a nano-film according to claim 1 or 4, characterized in that, The concentration of the NaBH 4 aqueous solution is 0.10 to 1.0 mmol / L, and the mass concentration of sodium citrate in the AgNO 3 or HAuCl 4 aqueous solution is 0.10 wt % to 2.0 wt %, and the concentration of AgNO 3 or HAuCl 4 is 0.10 to 0.50 mmol / L.

6. The method for in-situ preparation of a flexible SERS substrate based on a nano-film according to claim 3 or 4, characterized in that, The mass concentration of polyvinylpyrrolidone in the aqueous solution of Cd(NO 3 ) 2 or ZnCl 2 is 0.5 wt % to 3.0 wt %, the concentration of Cd(NO 3 ) 2 or ZnCl 2 is 0.01 to 0.1 mmol / L, and the concentration of the thioacetamide aqueous solution is 0.05 to 0.5 mmol / L.

7. The method for in-situ preparation of a flexible SERS substrate based on a nano-film according to any one of claims 1, 3, and 4, characterized in that, in step (2), by replacing the new reactant solution and changing the number of reactions, the particle size and particle gap of the noble metal or semiconductor nano-particles on the SERS substrate are regulated.

Images