Composite SERS (Surface Enhanced Raman Scattering) substrate based on metal organic framework as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of surface enhanced Raman spectroscopy, and particularly relates to a composite SERS (Surface Enhanced Raman Scattering) substrate based on a metal organic framework as well as a preparation method and application of the composite SERS substrate. Comprising the following steps: adding a polyvinylpyrrolidone solution into a metal organic framework nanoparticle solution, and modifying to obtain a self-assembly stock solution; a gold micro-nano junction array serves as a substrate, self-assembly liquid is dropwise added to the surface of the substrate, a first metal organic framework layer is formed through self-assembly construction, then the self-assembly liquid is dropwise added to the first metal organic framework layer, a second metal organic framework layer is formed through self-assembly construction, and the composite SERS substrate based on the metal organic framework is obtained. According to the method, the gold micro-nano junction array SERS is used as the substrate, two MOFs layers are formed on the surface of the substrate in a self-assembly construction mode, EC can be enriched and limited between the gold array SERS substrate and MOFs, and the stability and sensitivity of EC detection are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of surface enhanced Raman spectroscopy, and in particular relates to a composite SERS substrate based on a metal organic framework and a preparation method and application thereof. Background Art

[0002] Ethyl carbamate (EC) is a metabolite of arginine produced by yeast and lactic acid bacteria during wine fermentation. Its content is related to the quality of raw materials, brewing process and aging time. EC was classified as a Class 2A carcinogen in 2007. Currently, the EC content in different brands of wine has been tested, and the EC content ranges from 3.2ug / L to 291.2ug / L, which has a high safety risk, posing a potential threat to consumer health and the sustainable development of the wine industry.

[0003] The most common method for detecting ethyl carbamate content in wine is gas chromatography, but this method requires complex sample pretreatment and cumbersome steps, which cannot meet the requirements of rapid and large-scale detection. Based on this, it is of great significance to develop a simple and reliable method for rapid extraction and sensitive detection of EC in wine.

[0004] In recent years, surface enhanced Raman spectroscopy (SERS) has been used to qualitatively characterize the interactions between molecules and metal nanomaterials and detect various trace targets due to its excellent selectivity, ability to perform fingerprint recognition, and sensitivity that can reach single-molecule level detection. For example, Danting Yang, et al. Surface-enhanced Raman scattering for quantitative detection of ethyl carbamate in alcoholic beverages disclosed a new method for quantitative detection of ethyl carbamate in alcoholic beverages based on surface-enhanced Raman scattering (SERS). A single silver-coated gold nanoparticle colloid was used as a SERS amplifier to enhance the Raman enhancement of ethyl carbamate in three alcoholic beverages (vodka, Obstler and white rum); Yang D, et al. DFT study and quantitative detection by surface-enhanced Raman scattering (SERS) of ethyl carbamate [J]. Journal of Raman Spectroscopy, SERS spectra obtained by using silver nanoparticles reduced with hydroxylamine hydrochloride provided rapid and reproducible qualitative and quantitative determination of EC in aqueous solution; Qi, Haiyan, et al. Qualitative and quantitative detection of ethyl carbamate in wine using Surface-enhanced Raman By using flower-shaped silver nanoparticles as SERS testing platform, the application scope of quantitative model for EC determination was effectively expanded, which was feasible and reliable.

[0005] The above-mentioned noble metal nanoparticles as SERS substrate can achieve a good detection EC, but they are unstable and easily oxidized. The uneven size and shape of the metal nanoparticles lead to poor stability and low sensitivity. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a composite SERS substrate based on metal organic framework and its preparation method and application. Aiming at the problem that the existing SERS substrate has poor stability and low sensitivity in the rapid detection of trace harmful substance ethyl formate in wine, the metal organic framework (MOFs) material is covered on the gold display SERS substrate, so that the surface MOFs adsorption layer and the SERS array are efficiently integrated and the SERS array is accurately constructed on demand. A large number of EC molecules can be adsorbed through the MOFs adsorption layer, and EC is efficiently enriched for the detection of EC in wine, which has high sensitivity and accuracy in detecting EC in wine.

[0007] The present invention solves the above technical problems through the following technical solutions.

[0008] The first object of the present invention is to provide a method for preparing a composite SERS substrate based on a metal organic framework, comprising the following steps: S1. Adding polyvinyl pyrrolidone solution to the metal organic framework nanoparticle solution to modify the metal organic framework nanoparticles to obtain a self-assembly stock solution.

[0009] S2. The self-assembly stock solution is prepared into a self-assembly liquid, and the gold micro-nano junction array is used as the substrate. The self-assembly liquid is dropped on the surface of the substrate to self-assemble to form a first metal organic framework layer, and then the self-assembly liquid is dropped on the first metal organic framework layer to self-assemble to form a second metal organic framework layer, thereby obtaining a composite SERS substrate based on a metal organic framework.

[0010] Furthermore, the volume ratio of the metal organic framework nanoparticle solution to the polyvinyl pyrrolidone solution is 1:8-12, the concentration of the metal organic framework nanoparticle solution is 5wt%-20wt%, and the concentration of the polyvinyl pyrrolidone solution is 1.25wt%-2.5wt%.

[0011] Furthermore, the modification conditions are to react at 30°C to 50°C and 300r / min to 500r / min for 24h to 36h. After the modification, it is dispersed in ethanol to form a self-assembly stock solution. The concentration of the metal organic framework nanoparticles in the self-assembly stock solution is 8wt% to 12wt%; the self-assembly solution is prepared by mixing the self-assembly stock solution and water in a volume ratio of 1:1 to 3.

[0012] Furthermore, the self-assembly construction is to spread the self-assembly liquid on the surface of the substrate or the first metal organic framework layer, and then remove excess water and dry it after standing for 3h to 8h.

[0013] Furthermore, the thickness of the gold micro-nano junction array is 200nm-400nm, and the particle size of the metal organic framework nanoparticles is 150nm-650nm.

[0014] Furthermore, the method for preparing the metal organic framework nanoparticle solution comprises the following steps: The metal cation solution and the 2-methylimidazole organic ligand solution are mixed to carry out coordination polymerization to obtain metal organic framework nanoparticles, and the metal organic framework nanoparticles are dispersed in a solvent to obtain a metal organic framework nanoparticle solution, wherein the 2-methylimidazole organic ligand solution is a mixture of 2-methylimidazole, hexadecyltrimethylammonium bromide and a solvent.

[0015] Furthermore, the volume ratio of the metal cation solution and the 2-methylimidazole organic ligand solution is 1:1~3, the metal cation solution is an aqueous solution of zinc acetate dihydrate with a concentration of 0.5g / mL~0.8g / mL; the mass ratio of 2-methylimidazole, hexadecyltrimethylammonium bromide and water is 1.86g:0.24mg~0.98mg:8mL.

[0016] Furthermore, the coordination polymerization time is 1 h to 3 h, and the reaction temperature is room temperature.

[0017] The second object of the present invention is to provide the above preparation method to obtain a composite SERS substrate based on a metal organic framework.

[0018] The third object of the present invention is to provide the application of the above metal organic framework-based composite SERS substrate in detecting ethyl carbamate in wine.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) The preparation method of the composite SERS substrate based on metal organic framework provided by the present invention uses gold micro-nano junction array SERS as the substrate, and uses polyvinyl pyrrolidone-modified metal organic framework (MOFs) nanoparticles as adsorption active points. The self-assembly stock solution formed by the polyvinyl pyrrolidone-modified MOFs nanoparticles is covered on the gold micro-nano junction array SERS substrate, and the surface MOFs adsorption and SERS array are efficiently integrated and accurately constructed on demand to form a composite SERS substrate of metal organic framework, and two MOFs layers are self-assembled on the substrate surface. Pyrrolidone acts as a supporting skeleton for MOFs, improving the adhesion between MOFs particles in the first MOFs layer and the adjacent MOFs layer to form a solid MOFs layer. The gold micro-nanojunction array SERS substrate has the advantages of stable and uniform structure and abundant "hot spots". The MOFs particles in the MOFs layer have a large specific surface area and good stability. They can enrich EC and confine EC between the gold array SERS substrate and MOFs, solving the problem of low sensitivity caused by uneven size and shape of metal nanoparticles, and effectively improving the stability and sensitivity of EC detection.

[0020] (2) The present invention can adsorb a large number of EC molecules through the MOFs adsorption layer, and efficiently enrich EC for the detection of EC in wine. -7 M~1×10 -3 The linear relationship is good within the M range, and the minimum detection limit is 1×10 - 7 M, has high sensitivity and accuracy in detecting EC in wine. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The morphological structure diagrams of the single layer and double layer of MOFs nanoparticles of the present invention are shown in FIG. Figure 1 a in the figure is the single-layer morphology structure diagram of MOFs nanoparticles, and b is the cross-sectional morphology diagram of the double-layer of MOFs nanoparticles.

[0022] Figure 2 This is a morphological structure diagram of the first layer of MOFs and the second layer of MOFs constructed on the SERS substrate in Example 1 of the present invention. Figure 2 a in the figure is a cross-sectional morphology diagram of the first layer of MOFs constructed on the SERS substrate, and b is a cross-sectional morphology diagram of the second layer of MOFs constructed on the SERS substrate.

[0023] Figure 3 This is a graph showing the adsorption performance of ethyl carbamate by the MOFs nanoparticle layer of the present invention. Figure 3 Where a is the absorbance intensity at different times, and b is the adsorption amount at different times.

[0024] Figure 4 This is a graph showing the adsorption performance of ethyl carbamate adsorbed on the first metal organic framework layer formed in the SERS substrate construction of Example 1 of the present invention.

[0025] Figure 5 This is a Raman spectrum diagram of the composite SERS substrate based on a metal organic framework in Example 1 of the present invention.

[0026] Figure 6 This is a Raman spectrum diagram of the composite SERS substrate based on a metal organic framework in Example 1 of the present invention at different concentrations of ethyl formate.

[0027] Figure 7 This is a linear response relationship diagram of the Raman peak intensity and the concentration of ethyl formate detected by the composite SERS substrate based on the metal organic framework in Example 1 of the present invention for different concentrations of ethyl formate.

[0028] Figure 8 This is a graph showing the test results of the actual sample simulated by the spiked method of the present invention. Figure 8 (a) is the Raman spectrum of the standard sample, and (b) is the concentration of the spiked sample calculated based on the working curve. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] It should be noted that the professional terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, the various raw materials, reagents, instruments and equipment used in the following embodiments of the present invention can be purchased from the market or prepared by existing methods.

[0031] At present, using noble metal nanoparticles as SERS substrates can achieve better detection EC and SERS enhancement effect, but there are problems such as unstable properties and easy oxidation, and uneven size and shape of metal nanoparticles, resulting in low sensitivity. Based on the above problems, the present invention provides a method for preparing a composite SERS substrate based on a metal organic framework, comprising the following steps:

[0032] S1. Adding polyvinyl pyrrolidone solution to the metal organic framework nanoparticle solution to modify the metal organic framework nanoparticles to obtain a self-assembly stock solution.

[0033] S2. The self-assembly stock solution is prepared into a self-assembly liquid, and the gold micro-nano junction array is used as the substrate. The self-assembly liquid is dropped on the surface of the substrate to self-assemble to form a first metal organic framework layer, and then the self-assembly liquid is dropped on the first metal organic framework layer to self-assemble to form a second metal organic framework layer, thereby obtaining a composite SERS substrate based on a metal organic framework.

[0034] The present invention uses a gold micro-nano junction array SERS as a substrate, polyvinyl pyrrolidone-modified metal organic framework (MOFs) nanoparticles as adsorption active points, covers the gold micro-nano junction array SERS substrate with a self-assembly stock solution formed by the polyvinyl pyrrolidone-modified MOFs nanoparticles, efficiently integrates the surface MOFs adsorption with the SERS array, and accurately constructs a composite SERS substrate of the metal organic framework on demand, self-assembles and constructs two MOFs layers on the substrate surface, and polyvinyl pyrrolidone plays a supporting skeleton role for MOFs, thereby improving the adhesion between the MOFs particles in the first MOFs layer and the adjacent MOFs layer, and forming a firm MOFs layer, wherein the gold micro-nano junction array SERS substrate has the advantages of stable and uniform structure and rich "hot spots", the MOFs particles in the MOFs layer have a large specific surface area and good stability, can enrich EC and confine EC between the gold array SERS substrate and the MOFs, solves the problem of low sensitivity caused by uneven size and shape of metal nanoparticles, and effectively improves the stability and sensitivity of EC detection.

[0035] In a specific embodiment, the volume ratio of the metal organic framework nanoparticle solution to the polyvinyl pyrrolidone solution is 1:8-12, the concentration of the metal organic framework nanoparticle solution is 5wt%-20wt%, and the concentration of the polyvinyl pyrrolidone solution is 1.25wt%-2.5wt%. In a preferred embodiment, the volume ratio of the metal organic framework nanoparticle solution to the polyvinyl pyrrolidone solution is 1:10. In the present invention, after MOFs adsorbs polyvinyl pyrrolidone to the surface, polyvinyl pyrrolidone plays a supporting skeleton role for MOFs. Since the adhesion between the individual MOFs particles is not strong, it is difficult to form a strong monolayer film, so polyvinyl pyrrolidone is added as a skeleton support. However, polyvinyl pyrrolidone is adsorbed on the surface of MOFs and occupies certain adsorption sites, so it has an adverse effect on the adsorption of EC molecules. The present invention optimizes the amount of polyvinyl pyrrolidone added, and ensures that the adsorption amount of MOF on EC molecules meets the SERS detection requirements without affecting the firmness of the MOF particle monolayer film.

[0036] In a specific embodiment, the modification conditions are to react at 30°C to 50°C and 300r / min to 500r / min for 24h to 36h. After the modification, it is dispersed in ethanol to form a self-assembly stock solution. The concentration of metal organic framework nanoparticles in the self-assembly stock solution is 8wt% to 12wt%; the self-assembly liquid is prepared by the self-assembly stock solution and water in a volume ratio of 1:1 to 3. In the present invention, after the modification, it is necessary to centrifuge and wash with ethanol three times to remove the unmodified polyvinyl pyrrolidone to prevent the polyvinyl pyrrolidone from being adsorbed on the surface of MOFs and occupying too many adsorption sites.

[0037] In a specific embodiment, the self-assembly construction is to lay the self-assembly liquid on the substrate surface or the first metal organic framework layer, remove excess water after standing for 3h to 8h and dry. In the present invention, the self-assembly liquid is dripped on the substrate surface or the first metal organic framework layer until the substrate surface or the first metal organic framework layer is fully covered, and then stand to allow the MOFs particles in the self-assembly liquid to complete assembly, absorb excess water, and dry naturally.

[0038] In a specific embodiment, the thickness of the gold micro-nano junction array is 200 nm to 400 nm, and the particle size of the metal organic framework nanoparticles is 150 nm to 650 nm.

[0039] In a specific embodiment, the method for preparing the metal organic framework nanoparticle solution comprises the following steps: The metal cation solution and the 2-methylimidazole organic ligand solution are mixed to carry out coordination polymerization to obtain metal organic framework nanoparticles, and the metal organic framework nanoparticles are dispersed in a solvent to obtain a metal organic framework nanoparticle solution.

[0040] In a specific embodiment, the 2-methylimidazole organic ligand solution is a mixture of 2-methylimidazole, hexadecyltrimethylammonium bromide (CTAB) and a solvent, and the mass ratio of 2-methylimidazole, hexadecyltrimethylammonium bromide and water is 1.86g: 0.24~0.98mg: 8mL. The present invention can synthesize MOF nanoparticles of different sizes by controlling the amount of 2-methylimidazole ligand and surfactant hexadecyltrimethylammonium bromide. While keeping the concentration and volume of the metal cation solution unchanged, 1.86g of 2-methylimidazole and 0.98mg of CTAB ligand solution can synthesize 150nm~200nm MOFs nanoparticles, and 1.86g of 2-methylimidazole and 0.24mg of CTAB ligand solution can synthesize 600nm~650nm MOFs nanoparticles.

[0041] In a specific embodiment, the volume ratio of the metal cation solution to the 2-methylimidazole organic ligand solution is 1:1 to 3, and the metal cation solution is a zinc acetate dihydrate aqueous solution with a concentration of 0.5 g / mL to 0.8 g / mL. In a preferred embodiment, the volume ratio of the metal cation solution to the 2-methylimidazole organic ligand solution is 1:1, and the concentration of the zinc acetate dihydrate aqueous solution is 0.0625 g / mL. By controlling the volume ratio of the zinc acetate dihydrate aqueous solution to the 2-methylimidazole organic ligand solution and the concentration of the zinc acetate dihydrate aqueous solution, the MOFs structure is stable and the adsorption is strong.

[0042] In a specific embodiment, the coordination polymerization time is 1 h to 3 h, and the reaction temperature is room temperature.

[0043] The present invention provides a composite SERS substrate based on a metal organic framework obtained by the above preparation method.

[0044] The present invention also provides the use of the metal organic framework-based composite SERS substrate in detecting ethyl carbamate in wine. The present invention can adsorb a large number of EC molecules through the MOFs adsorption layer, and efficiently enrich EC for the detection of EC in wine. -7 ~1×10 -3 The linear relationship is good within the M range, and the minimum detection limit is 1×10 - 7 M, has high sensitivity and accuracy in detecting EC in wine.

[0045] The invention is further described below through specific examples.

[0046] Example 1 A method for preparing a composite SERS substrate based on a metal organic framework comprises the following steps: S1. Preparation of Metal Organic Framework MOFs Nanoparticles: 0.5 g of zinc acetate dihydrate was dissolved in 8 mL of deionized water, which was called a metal cation solution; 1.86 g of 2-methylimidazole and 0.98 mg of hexadecyltrimethylammonium bromide were uniformly mixed with 8 mL of deionized water, which was called a 2-methylimidazole organic ligand solution.

[0047] The metal cation solution and the 2-methylimidazole organic ligand solution were poured into a small bottle at a volume ratio of 1:1 at the same time and gently stirred for about 10 seconds. The solution turned light blue and gradually turned milky white, and then stood for 2 hours for coordination polymerization to allow the metal cations and ligands to react fully. After the reaction, the solution was centrifuged at 8000 rpm for 10 minutes to remove the unreacted reagents and surfactants, and was washed three times by centrifugation with deionized water to obtain MOFs nanoparticles, which were stored in deionized water for later use to form a MOFs nanoparticle solution. The concentration of the MOFs nanoparticle solution was 5wt%.

[0048] S2. Preparation of self-assembly stock solution of MOFs nanoparticles: Take S1 to obtain 1 mL of MOFs nanoparticle solution, add 10 mL of 2.5% wt PVP aqueous solution, and carry out modification reaction at 30 °C and 500 r / min for 24 h, then centrifuge and wash with ethanol 3 times, and finally disperse in 500 μL of ethanol as the assembly stock solution. The concentration of metal organic framework nanoparticles in the self-assembly stock solution is 10 wt%.

[0049] S3. Preparation of composite SERS substrate: The self-assembly liquid is prepared by mixing the self-assembly stock solution and water in a volume ratio of 1:1. The gold micro-nanojunction array is used as the substrate, and the self-assembly liquid is dropped on the surface of the substrate. After the MOFs are assembled on the water surface, the excess water is absorbed and the layer is dried naturally to form the first metal organic framework layer. Then, the self-assembly liquid is dropped on the first metal organic framework layer. After the MOFs are assembled on the water surface, the excess water is absorbed and the layer is dried naturally to form the second metal organic framework layer, thereby obtaining a composite SERS substrate based on a metal organic framework.

[0050] Example 2 A method for preparing a composite SERS substrate based on a metal organic framework comprises the following steps: S1. Preparation of Metal Organic Framework MOFs Nanoparticles: 0.5 g of zinc acetate dihydrate was dissolved in 8 mL of deionized water, which was called a metal cation solution; 1.86 g of 2-methylimidazole and 0.24 mg of hexadecyltrimethylammonium bromide were uniformly mixed with 8 mL of deionized water, which was called a 2-methylimidazole organic ligand solution.

[0051] The metal cation solution and the 2-methylimidazole organic ligand solution were poured into a small bottle at a volume ratio of 1:1 at the same time and gently stirred for about 10 seconds. The solution turned light blue and gradually turned milky white, and then stood for 2 hours for coordination polymerization to allow the metal cations and ligands to react fully. After the reaction, the solution was centrifuged at 8000 rpm for 10 minutes to remove the unreacted reagents and surfactants, and was washed three times by centrifugation with deionized water to obtain MOFs nanoparticles, which were stored in deionized water for later use to form a MOFs nanoparticle solution. The concentration of the MOFs nanoparticle solution was 5wt%.

[0052] S2. Preparation of self-assembly stock solution of MOFs nanoparticles: Take S1 to obtain 1 mL of MOFs nanoparticle solution, add 10 mL of 2.5% wt PVP aqueous solution, and carry out modification reaction at 30 °C and 500 r / min for 24 h, then centrifuge and wash with ethanol 3 times, and finally disperse in 500 μL of ethanol as the assembly stock solution. The concentration of metal organic framework nanoparticles in the self-assembly stock solution is 10 wt%.

[0053] S3. Preparation of composite SERS substrate: The self-assembly liquid is prepared by mixing the self-assembly stock solution and water in a volume ratio of 1:1. The gold micro-nanojunction array is used as the substrate, and the self-assembly liquid is dropped on the surface of the substrate. After the MOFs are assembled on the water surface, the excess water is absorbed and the layer is dried naturally to form the first metal organic framework layer. Then, the self-assembly liquid is dropped on the first metal organic framework layer. After the MOFs are assembled on the water surface, the excess water is absorbed and the layer is dried naturally to form the second metal organic framework layer, thereby obtaining a composite SERS substrate based on a metal organic framework.

[0054] Example 3 A method for preparing a composite SERS substrate based on a metal organic framework comprises the following steps: S1. Preparation of Metal Organic Framework MOFs Nanoparticles: 0.5 g of zinc acetate dihydrate was dissolved in 8 mL of deionized water, which was called a metal cation solution; 1.86 g of 2-methylimidazole and 0.24 mg of hexadecyltrimethylammonium bromide were uniformly mixed with 8 mL of deionized water, which was called a 2-methylimidazole organic ligand solution.

[0055] The metal cation solution and the 2-methylimidazole organic ligand solution were poured into a small bottle at a volume ratio of 1:1 at the same time and gently stirred for about 10 seconds. The solution turned light blue and gradually turned milky white, and then stood for 2 hours for coordination polymerization to allow the metal cations and ligands to react fully. After the reaction, the solution was centrifuged at 8000 rpm for 10 minutes to remove the unreacted reagents and surfactants, and was washed three times by centrifugation with deionized water to obtain MOFs nanoparticles, which were stored in deionized water for later use to form a MOFs nanoparticle solution. The concentration of the MOFs nanoparticle solution was 8wt%.

[0056] S2. Preparation of self-assembly stock solution of MOFs nanoparticles: Take S1 to obtain 1 mL of MOFs nanoparticle solution, add 10 mL of 2.5% wt PVP aqueous solution, and react at 30 °C and 500 r / min for 24 h. Then centrifuge and wash with ethanol three times, and finally disperse in 800 μL of ethanol as the assembly stock solution. The concentration of metal organic framework nanoparticles in the self-assembly stock solution is 10 wt%.

[0057] S3. Preparation of composite SERS substrate: The self-assembly liquid is prepared by mixing the self-assembly stock solution and water in a volume ratio of 1:3. The gold micro-nanojunction array is used as the substrate, and the self-assembly liquid is dropped on the surface of the substrate. After the MOFs are assembled on the water surface, the excess water is absorbed and the substrate is dried naturally to form the first metal organic framework layer. Then, the self-assembly liquid is dropped on the first metal organic framework layer. After the MOFs are assembled on the water surface, the excess water is absorbed and the substrate is dried naturally to form the second metal organic framework layer, thereby obtaining a composite SERS substrate based on a metal organic framework.

[0058] Example 4 A method for preparing a composite SERS substrate based on a metal organic framework comprises the following steps: S1. Preparation of Metal Organic Framework MOFs Nanoparticles: 0.5 g of zinc acetate dihydrate was dissolved in 8 mL of deionized water, which was called a metal cation solution; 1.86 g of 2-methylimidazole and 0.24 mg of hexadecyltrimethylammonium bromide were uniformly mixed with 8 mL of deionized water, which was called a 2-methylimidazole organic ligand solution.

[0059] The metal cation solution and the 2-methylimidazole organic ligand solution were poured into a small bottle at a volume ratio of 1:1 at the same time and gently stirred for about 10 seconds. The solution turned light blue and gradually turned milky white, and then stood for 2 hours for coordination polymerization to allow the metal cations and ligands to react fully. After the reaction, the solution was centrifuged at 8000 rpm for 10 minutes to remove the unreacted reagents and surfactants, and was washed three times by centrifugation with deionized water to obtain MOFs nanoparticles, which were stored in deionized water for later use to form a MOFs nanoparticle solution. The concentration of the MOFs nanoparticle solution was 20wt%.

[0060] S2. Preparation of self-assembly stock solution of MOFs nanoparticles: Take S1 to obtain 1 mL of MOFs nanoparticle solution, add 10 mL of 2.5% wt PVP aqueous solution, and carry out modification reaction at 30 °C and 500 r / min for 24 h, then centrifuge and wash with ethanol 3 times, and finally disperse in 2000 μL of ethanol as the assembly stock solution. The concentration of metal organic framework nanoparticles in the self-assembly stock solution is 10 wt%.

[0061] S3. Preparation of composite SERS substrate: The self-assembly liquid is prepared by mixing the self-assembly stock solution and water in a volume ratio of 1:2. The gold micro-nano junction array is used as the substrate and the self-assembly liquid is dropped on the substrate surface. After the MOFs are assembled on the water surface, the excess water is absorbed and the substrate is dried naturally to form the first metal organic framework layer. Then, the self-assembly liquid is dropped on the first metal organic framework layer. After the MOFs are assembled on the water surface, the excess water is absorbed and the substrate is dried naturally to form the second metal organic framework layer, thereby obtaining a composite SERS substrate based on a metal organic framework.

[0062] The metal organic framework-based composite SERS substrates prepared in Examples 1 to 4 have similar structures and similar effects. Taking the metal organic framework-based composite SERS substrate prepared in Example 1 as an example, the structure and performance of the MOFs nanoparticles and the composite SERS substrate prepared in Example 1 are tested, and the results are as follows: The preparation method of the single layer of MOFs nanoparticles and the double layer of MOFs nanoparticles comprises the following steps: The monolayer self-assembly of MOFs nanoparticles is based on a silicon wafer (hydrophilic treatment) covered with water. The self-assembly liquid is dripped on the surface of the substrate. After the MOFs are assembled on the water surface, the excess water is absorbed and the membrane is naturally dried to form a monolayer. Self-assembly liquid is then dripped on the monolayer membrane. After the MOFs are assembled on the water surface, the excess water is absorbed and the second layer is naturally dried.

[0063] Figure 1 The morphological structure diagrams of the single layer and double layer of MOFs nanoparticles of the present invention are shown in FIG. Figure 1 a in the figure is the morphological structure diagram of a single layer of MOFs nanoparticles, and b is the cross-sectional morphology diagram of a double layer of MOFs nanoparticles. Figure 1 As shown, the particle size of MOFs nanoparticles is between 150nm and 200nm. By adding self-assembly liquid to the monolayer film, MOFs nanoparticles can be accumulated to form a double-layer structure.

[0064] Figure 2 This is a morphological structure diagram of the first layer of MOFs and the second layer of MOFs constructed on the SERS substrate in Example 1 of the present invention. Figure 2 a in FIG. 1 is a cross-sectional morphology diagram of the first layer of MOFs constructed on the SERS substrate, and b is a cross-sectional morphology diagram of the second layer of MOFs constructed on the SERS substrate. Figure 2 As shown, the synthesized MOFs material is laid on the SERS substrate to form a first MOFs layer; the synthesized MOFs layer is laid on the SERS substrate and dried and then another MOFs layer is laid to form a second MOFs layer, thereby obtaining a composite SERS substrate based on a metal organic framework.

[0065] The MOFs nanoparticle layer prepared in Example 1 was subjected to an adsorption test of ethyl formate, which specifically includes the following steps: The concentration is 10 -4 mol / L ethyl carbamate ethanol solution, add MOFs nanoparticle layer and mix and stir for 20 minutes. Under the reaction conditions of 30℃ and 500r / min, the MOFs nanoparticle layer measures the light absorption spectrum of the solution after adsorption for 10min, 20min, 30min, 40min, 50min and 60min respectively. The test method of light absorption spectrum is as follows:

[0066] The adsorbed solution was mixed with 10 -4 mol / L phosphoric acid, 10 -4 The three mol / L o-phthalaldehyde solutions were mixed and stirred for 20 min at 30°C and 500 r / min. The light absorption spectrum of the solution after the reaction was tested.

[0067] Among them, ethyl carbamate reacts with an indicator molecule (o-phthalaldehyde) with a light absorption peak. Since -NH2 (amino) and -OR (alkoxy) in ethyl carbamate are auxochromophores, the absorbance of the indicator molecule will increase after reacting with the indicator. Therefore, the concentration of ethyl carbamate can be indirectly analyzed quantitatively by using the intensity change of the absorbance of the indicator molecule before and after the reaction.

[0068] Figure 3 This is a graph showing the adsorption performance of ethyl carbamate by the MOFs nanoparticle layer of the present invention. Figure 3 Where a is the absorbance intensity at different times, and b is the adsorption amount at different times. Figure 3 As shown in the figure, the UV spectrum and absorbance of the amount of EC adsorbed by the MOFs nanoparticle layer at different times, the adsorption amount increases with the extension of the adsorption time, and the adsorption amount is the largest at 30 minutes.

[0069] The first metal organic framework layer formed by the SERS substrate construction in Example 1 was subjected to an adsorption test of ethyl formate, which specifically includes the following steps: The first metal organic framework layer of the SERS substrate was constructed and placed in 1L of 10 -4 mol / L ethyl formate ethanol solution, immersed at 30℃ for 10min, taken out and dried naturally, and Raman spectroscopy was measured. The spectral acquisition conditions were: excitation wavelength of 785nm, energy of 15mW, integration time of 5s, and integration times of 1. The sample of the first metal organic framework layer formed by constructing the SERS substrate without adsorption was used as a blank control.

[0070] Figure 4This is a graph showing the adsorption performance of ethyl carbamate when the first metal organic framework layer is adsorbed on the SERS substrate in Example 1 of the present invention. Figure 4 As shown in Example 1, after the first metal organic framework layer is constructed to adsorb ethyl carbamate, the -1 、1016cm -1 、1133cm -1 、1176cm -1 、1359cm -1 and 1462cm -1 Significant Raman vibration peaks can be detected at 689cm -1 The Raman peak intensity is about 5000.

[0071] The metal organic framework-based composite SERS substrate prepared in Example 1 was subjected to a urethane adsorption test, which specifically includes the following steps: The metal organic framework-based composite SERS substrate samples prepared in Example 1 were placed in 1L, 2L and 3L of 10 -4 mol / L ethyl formate ethanol solution, immersed at 30℃ for 10min, taken out and dried naturally, and Raman spectrum measurement was performed. The spectrum acquisition conditions were: excitation wavelength of 785nm, energy of 15mW, integration time of 5s, and integration times of 1. The non-adsorbed metal-organic framework-based composite SERS substrate sample was used as a blank control.

[0072] Figure 5 This is a Raman spectrum of the composite SERS substrate based on a metal organic framework in Example 1 of the present invention. Figure 5 As shown in the figure, in ethyl carbamate ethanol solutions of the same concentration and different volumes, the Raman vibration peak position of the Raman spectrum of ethyl carbamate adsorbed by the metal organic framework-based composite SERS substrate prepared in Example 1 is the same, at 689 cm -1 、1016cm -1 、1133cm -1 、1176cm -1 、1359cm -1 and 1462cm -1 A significant Raman vibration peak can be measured at 689cm -1 There is a significant difference, at a concentration of 10 -4 mol / L ethyl carbamate ethanol solution, its 689cm -1 The Raman peak intensity is about 15000.

[0073] The metal organic framework based composite SERS substrate prepared in Example 1 was placed in 2L of 10 -3 mol / L、10 -4 mol / L、10 -5 mol / L、10 -6 mol / L ethyl formate ethanol solution, immersed at 30℃ for 10min, taken out and dried naturally, and Raman spectrum measurement was carried out. The spectrum collection conditions were: excitation wavelength of 785nm, energy of 15mW, integration time of 5s, and integration times of 1. Figure 6 The Raman spectra of the composite SERS substrate based on the metal organic framework in Example 1 of the present invention at different concentrations of urethane are shown in FIG. Figure 6 As shown in the figure, when the concentration of ethyl formate solution increases from 10 -3 mol / L decreased to 10 - 7 mol / L,689cm -1 、1016cm -1 、1133cm -1 、1176cm -1 、1359cm -1 and 1462cm -1 The intensity of the Raman vibration peak at 689 cm -1 The Raman peak at 10 -7 mol / L ethyl carbamate solution can still be measured.

[0074] The metal organic framework-based composite SERS substrate prepared according to Example 1 was -1 The Raman peak intensity changes at the urethane peak, the linear response relationship between different concentrations of ethyl formate and the Raman absorption spectrum light intensity was constructed, and the fitting curve of Raman spectrum light intensity and ethyl formate concentration was drawn. The curve with the highest fitting degree was selected as the standard curve for ethyl formate detection. Figure 7 The linear response relationship between the Raman peak intensity and the concentration of ethyl formate detected by the composite SERS substrate based on the metal organic framework in Example 1 of the present invention is shown in FIG. Figure 7 As shown, at a concentration of 1×10 - 7 M~1×10 -3 The linear relationship is good within the range of M, and the curve with the highest fitting degree is selected as the standard curve for ethyl carbamate detection, y=3.3694.0+4787.4x, R 2 =0.99697, the minimum detection limit is 1×10 -7 M, indicating that the method established by the present invention has high sensitivity and accuracy for detecting EC in wine.

[0075] In order to verify the effectiveness and reliability of the designed metal-organic framework-based composite SERS substrate for detecting EC concentration in wine, the EC in wine was detected by spiking method to simulate the actual sample detection. -5 The composite SERS substrate was placed in urethane solutions of different concentrations (spiked samples) at 30 °C for 10 min, taken out and dried naturally, and Raman spectra were measured. The spectrum acquisition conditions were: excitation wavelength 785 nm, energy 15 mW, integration time 5 s, and integration times 1. The experimental results are shown in Figure 8 shown.

[0076] Figure 8 This is a graph showing the test results of the actual sample simulated by the spiked method of the present invention. Figure 8 Where a is the Raman spectrum of the standard sample, and b is the concentration of the spiked sample calculated based on the working curve. Figure 8 As shown in the figure, the collected spectral lines are successively de-baselined and the 689cm -1 The Raman peak intensity at 14056 was substituted into the standard working curve, and the calculated concentration of ethyl formate was 4.89×10 -5 M, indicating that the metal-organic framework-based composite SERS substrate has good detection performance for EC in wine.

[0077] It should be noted that when the present invention involves a numerical range, it should be understood that the two endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as those in the embodiments, in order to avoid redundancy, the present invention describes a preferred embodiment. Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the attached claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0078] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for preparing a composite SERS substrate based on a metal organic framework, characterized in that: The following steps are involved: Adding polyvinyl pyrrolidone solution to the metal organic framework nanoparticle solution to modify the metal organic framework nanoparticles to obtain a self-assembly stock solution; The self-assembly stock solution is prepared into a self-assembly liquid, and the gold micro-nano junction array is used as the substrate. The self-assembly liquid is dropped on the surface of the substrate to self-assemble to form a first metal organic framework layer. Then, the self-assembly liquid is dropped on the first metal organic framework layer to self-assemble to form a second metal organic framework layer, thereby obtaining a composite SERS substrate based on a metal organic framework.

2. The method for preparing a metal organic framework-based composite SERS substrate according to claim 1, characterized in that: The volume ratio of the metal organic framework nanoparticle solution to the polyvinyl pyrrolidone solution is 1:8-12, the concentration of the metal organic framework nanoparticle solution is 5wt%-20wt%, and the concentration of the polyvinyl pyrrolidone solution is 1.25wt%-2.5wt%.

3. The method for preparing a metal organic framework-based composite SERS substrate according to claim 1, characterized in that: The modification conditions are to react at 30°C to 50°C and 300r / min to 500r / min for 24h to 36h. After the modification, it is dispersed in ethanol to form a self-assembly stock solution. The concentration of the metal organic framework nanoparticles in the self-assembly stock solution is 8wt% to 12wt%; the self-assembly solution is prepared by mixing the self-assembly stock solution and water in a volume ratio of 1:1 to 3.

4. The method for preparing a metal organic framework-based composite SERS substrate according to claim 1, characterized in that: The self-assembly construction is to spread the self-assembly liquid on the surface of the substrate or the first metal organic framework layer, remove excess water and dry it after standing for 3h to 8h.

5. The method for preparing a metal organic framework-based composite SERS substrate according to claim 1, characterized in that: The thickness of the gold micro-nano junction array is 200nm-400nm, and the particle size of the metal organic framework nanoparticles is 150nm-650nm.

6. The method for preparing a metal organic framework-based composite SERS substrate according to claim 1, characterized in that: The method for preparing a metal organic framework nanoparticle solution comprises the following steps: The metal cation solution and the 2-methylimidazole organic ligand solution are mixed to carry out coordination polymerization to obtain metal organic framework nanoparticles, and the metal organic framework nanoparticles are dispersed in a solvent to obtain a metal organic framework nanoparticle solution, wherein the 2-methylimidazole organic ligand solution is a mixture of 2-methylimidazole, hexadecyltrimethylammonium bromide and a solvent.

7. The method for preparing a metal organic framework-based composite SERS substrate according to claim 6, characterized in that: The volume ratio of the metal cation solution to the 2-methylimidazole organic ligand solution is 1:1-3, the metal cation solution is an aqueous solution of zinc acetate dihydrate with a concentration of 0.5 g / mL-0.8 g / mL; the mass ratio of 2-methylimidazole, hexadecyltrimethylammonium bromide and water is 1.86 g:0.24 mg-0.98 mg:8 mL.

8. The method for preparing a metal organic framework-based composite SERS substrate according to claim 6, characterized in that: The coordination polymerization time is 1 h to 3 h, and the reaction temperature is room temperature.

9. A composite SERS substrate based on a metal organic framework obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the metal organic framework-based composite SERS substrate according to claim 9 in detecting ethyl carbamate in wine.

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