Preparation method and application of composite SERS (Surface Enhanced Raman Scattering) substrate with Raman active interface structure and internal standard

Abstract

The invention discloses a preparation method and application of a composite SERS (Surface Enhanced Raman Scattering) substrate with a Raman active interface structure and an internal standard. The composite SERS substrate is obtained by inducing a noble metal precursor to nucleate and grow on the surface of an MOF (Metal Organic Framework) by utilizing a polydopamine engineering strategy. The preparation method of the MOF and precious metal composite SERS substrate is simple and efficient, has universality, has a high Raman activity interface structure and an internal standard, can greatly enhance Raman signals of molecules to be detected, and improves the accuracy and reliability of SERS detection results at the same time.

Description

Technical Field

[0001] The invention relates to a preparation method of a composite SERS substrate with a Raman active interface structure and an internal standard and application thereof, and belongs to the technical field of nano material science and surface enhanced Raman spectroscopy detection. Background Art

[0002] Surface enhanced Raman scattering (SERS) technology has the advantages of molecular fingerprint recognition, high sensitivity, and rapid non-destructive detection. It has been widely used in the identification and detection of various trace species. The SERS effect mainly comes from the electromagnetic field enhancement caused by surface plasmon resonance, which is particularly prominent in the gaps between adjacent noble metal nanoparticles. At the same time, as a near-field enhancement phenomenon, SERS can only greatly enhance its Raman signal when the molecules to be detected are located in these "hot spots". However, the interaction between typical organic pollutants such as phenols and polycyclic aromatic hydrocarbons and traditional noble metal substrates is very weak, which will result in weak or even no SERS detection signals. Therefore, the preparation of SERS substrates with excellent adsorption and enrichment capabilities and Raman signal enhancement effects remains a challenging task.

[0003] Compared with single-component noble metal substrates, the development of multi-component composite substrates with synergistic effects is expected to enrich the molecules to be detected on the surface of the "hot spot" structure, thereby improving the sensitivity of SERS detection. Metal-organic framework (MOF) materials have become ideal candidate materials for the preparation of composite SERS substrates due to their highly adjustable structure, large specific surface area and strong adsorption capacity. At present, there are three main ways to prepare this MOF-precious metal composite substrate: (1) using the solution impregnation method to embed precious metal nanoparticles inside the MOF (Anal. Chem., 2014, 86: 3955~3963); (2) using the seed growth method or the one-step solvothermal method to coat the MOF shell structure on the surface of the precious metal nanoparticles (Anal. Chem. 2021, 93, 7188~7195; Angew. Chem., 2013, 125, 3829~3833); (3) using the in situ reduction method or the decoration method to load precious metal nanoparticles on the outer surface of MOF (Anal. Chem. 2015, 87, 12177~12182; patent CN107478635A). Due to the formation of a large number of Raman "hotspot" structures on the MOF surface, the Raman signals of the molecules to be detected adsorbed on the noble metal surface or located at the MOF-noble metal interface will be significantly enhanced. Based on this, the third preparation method can expand the types of molecules detected by SERS (including molecules with strong, weak and no interaction forces with noble metals) and significantly improve the SERS signal and detection sensitivity. However, this composite SERS substrate has not been widely used in the quantitative analysis of trace species. One of the main reasons is the lack of a simple, efficient and universal strategy to prepare a composite SERS substrate with controllable "hotspot" structure and Raman active interface structure on the MOF surface. In addition, this type of composite substrate also has the disadvantages of uneven morphology and poor stability, which will lead to the instability of SERS detection signals. Summary of the invention

[0004] In view of the deficiencies of the above-mentioned prior art, the present invention provides a method for preparing a composite SERS substrate having a Raman active interface structure and an internal standard and its application. The technical problem to be solved is to design and select a simple, efficient and universal strategy to prepare a composite SERS substrate with noble metal nanoparticles loaded on the outer surface of MOF, so as to solve the problems of low loading efficiency of noble metal nanoparticles, inability to accurately control the Raman "hot spot" structure, poor stability and fluctuation of detection signals existing in such composite SERS substrates, and to use it for quantitative detection of phenolic compounds in actual environments and biological samples.

[0005] The present invention uses polydopamine (PDA) engineering strategy to induce the nucleation and growth of noble metal precursors on the MOF surface to obtain a MOF@noble metal composite SERS substrate. By precisely controlling the particle size and adjacent gaps of noble metal nanoparticles, a MOF-noble metal interface structure with high SERS activity is constructed. At the same time, the strong adsorption and enrichment ability of MOF and the stable Raman internal standard signal are used to achieve high-sensitivity detection and quantitative analysis of the molecules to be tested.

[0006] The preparation method of the composite SERS substrate with Raman active interface structure and internal standard of the present invention forms an adhesive PDA layer on the surface of MOF by utilizing PDA engineering strategy, and obtains it by nucleating and growing noble metal on the surface.

[0007] The MOF material is MIL-101 or UIO-66.

[0008] The noble metal nanoparticles are gold nanoparticles (AuNPs) or silver nanoparticles (AgNPs).

[0009] The specific steps include: Step 1: Disperse 30 mg of MOF material in 20 mL of 10 mM Tris buffer, add 90 mg of dopamine, stir the reaction at room temperature for 12 h, centrifuge and wash to obtain MOF@PDA.

[0010] Step 2: Nucleation and growth of precious metals 2a. Re-disperse the MOF@PDA obtained in step 1 in the silver ammonia solution, stir and react at room temperature for 1 h, add 10 mL of 5 mg / mL glucose solution, continue to stir and react at room temperature for 5-30 min, centrifuge and wash to obtain MOF@AgNPs.

[0011] 2b. Re-disperse the MOF@PDA obtained in step 1 in 20 mL of 2.5 mM chloroauric acid solution, add 200 μL of 1.0 M sodium borohydride solution dropwise, stir and react at room temperature for 1 h, centrifuge and wash, then disperse in gold growth solution again, continue stirring and react at room temperature for 5-30 min, centrifuge and wash to obtain MOF@AuNPs.

[0012] In the above reaction process, the particle size and adjacent gaps of the noble metal nanoparticles are regulated by the reaction time. At the beginning, as the reaction time increases, the particle size gradually increases, the adjacent gaps gradually decrease, and the detection signal gradually increases; however, when the particle size increases to a certain extent, the adjacent gaps increase instead, which leads to a decrease in the detection signal. Figure 3 The signal is strongest at 30 min, and then decreases.

[0013] In step 1, the pH of the Tris buffer is 8.5.

[0014] In step 2a, the silver ammonia solution is prepared by dissolving 0.5 g of silver nitrate in 50 mL of ultrapure water, and adding ammonia water dropwise until the initially generated precipitate is just dissolved, thereby obtaining the silver ammonia solution.

[0015] In step 2b, the gold growth solution is prepared by dissolving 1 g of polyvinyl pyrrolidone and 0.3 g of potassium iodide in 9 mL of ultrapure water, and adding 1 mL of 2 M ascorbic acid and 10 mL of 50 mM chloroauric acid to obtain the gold growth solution.

[0016] In the composite SERS substrate with Raman active interface structure and internal standard of the present invention, the Raman active interface structure is the interface structure of MOF-noble metal composite material, and the Raman internal standard is the characteristic peak of organic ligand terephthalic acid in the MOF structure.

[0017] The invention discloses an application of a composite SERS substrate with a Raman active interface structure and an internal standard in the detection of phenolic compounds.

[0018] The phenolic compound is 1-naphthol or 2-naphthol.

[0019] Specifically, the relative intensity of the characteristic peak of the phenolic compound and the internal standard peak is used as a signal parameter to achieve quantitative detection of the phenolic compound in the sample to be tested.

[0020] The sample to be tested is a liquid, including a water sample or a biological sample, such as river water, urine, etc.

[0021] The detection method is as follows: The concentrations were 1.0 × 10 -6 M, 5.0 × 10 -6 M, 1.0 × 10 -5 M, 1.0 × 10 -4 M and 1.0 × 10 -3 100 μL of the above phenolic compound aqueous solution of different concentrations was taken and mixed with 900 μL of 0.2 mg / mL composite SERS substrate suspension and shaken at room temperature for 90 min. 20 μL of the obtained solution was dropped on a clean silicon wafer for Raman spectroscopy test. -1 and 1603 cm -1 The Raman intensity ratio I 1062 / I 1603 The standard curve is obtained with the logarithmic concentration of phenolic compounds as the vertical coordinate and used for the quantitative detection of phenolic compounds in the samples to be tested.

[0022] Compared with the existing technology, the composite SERS substrate with noble metal nanoparticles loaded on the outer surface of MOF prepared by PDA engineering strategy has the following advantages and beneficial effects: 1. The composite SERS substrate of the present invention is obtained through a simple, efficient and universal PDA engineering strategy, in which PDA plays the role of stabilizer, reducing agent and bridging agent.

[0023] 2. The composite SERS substrate of the present invention has a Raman active interface structure, and its Raman activity can be optimized by regulating the particle size and adjacent gaps of the noble metal nanoparticles, which can expand the types of molecules detected by SERS and greatly enhance the Raman signals of the molecules to be detected near the interface.

[0024] 3. The present invention utilizes the MOF characteristic peak signal in the composite SERS substrate as the Raman internal standard, which can effectively avoid the problem of detection signal fluctuation caused by environmental factors and uneven substrate morphology, and improve the accuracy and reliability of SERS detection results. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the preparation of the composite SERS substrate with Raman active interface structure and internal standard in the present invention.

[0026] Figure 2 The transmission electron micrographs of the MIL-101@Ag seeds and MIL-101@AgNPs prepared in Example 1 of the present invention are shown in FIG. a is the MIL-101@Ag seeds; bd are the MIL-101@AgNPs obtained after the seed growth time is 5, 15, and 30 min, respectively.

[0027] Figure 3 The test results of the seed growth time on the composite SERS substrate enhancement effect in Example 4 of the present invention are shown in Figure 1. a is the Raman spectrum of MIL-101 and MIL-101@AgNPs obtained with a seed growth time of 30 min; b is the internal standard peak 1603 cm in MIL-101@Ag seeds and MIL-101@AgNPs obtained with seed growth times of 5, 15, and 30 min, respectively. -1 Comparison of Raman intensities at .

[0028] Figure 4 This is the test result of the stability of the composite SERS substrate in Example 4 of the present invention.

[0029] Figure 5 The results of the composite SERS substrate for detecting 1-naphthol in aqueous solution in Example 4 of the present invention are shown in Figure 4. Wherein, a is the SERS spectra of 1-naphthol at different concentrations; b is the linear relationship diagram established by the method.

[0030] Figure 6 This is the SERS spectra of MIL-101@AgNPs and AgNPs mixed with 1-naphthol in Example 4 of the present invention.

[0031] Figure 7 This is a SERS spectrum diagram of the composite SERS substrate in Example 5 of the present invention for detecting 1-naphthol in a river water sample.

[0032] Figure 8 This is a SERS spectrum diagram of the composite SERS substrate in Example 6 of the present invention for detecting 1-naphthol in a urine sample. DETAILED DESCRIPTION

[0033] In order to further understand the present invention, the technical solutions in the embodiments of the present invention are clearly and completely described below in combination with the drawings and specific embodiments of the specification. Obviously, the described embodiments are 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. Embodiment 1:

[0034] The preparation method of the composite SERS substrate having a Raman active interface structure and an internal standard in this embodiment comprises the following specific steps: 1. Preparation of MOF materials—MIL-101 400 mg of chromium nitrate nonahydrate and 166 mg of terephthalic acid were ultrasonically dissolved in 4.8 mL of ultrapure water, 67.4 μL of concentrated nitric acid was added, and then transferred to a 50 mL hydrothermal reactor and reacted at 220 °C for 8 h; after cooling to room temperature, the obtained product was washed with ultrapure water, N,N-dimethylformamide and anhydrous ethanol for 3 times each; finally, the product was vacuum dried at 120 °C for 2 h to obtain MIL-101.

[0035] 2. Preparation of MOF@PDA—MIL-101@PDA 30 mg of MIL-101 material was dispersed in 20 mL of 10 mM Tris buffer, 90 mg of dopamine was added, and the reaction was stirred at room temperature for 12 h. MIL-101@PDA was obtained after centrifugation and washing.

[0036] 3. Preparation of MOF@precious metal composite SERS substrate—MIL-101@AgNPs Dissolve 0.5 g of silver nitrate in 50 mL of ultrapure water, add ammonia water dropwise until the initially generated precipitate is just dissolved, and obtain a silver-ammonia solution; redisperse the MIL-101@PDA obtained in step 2 in the silver-ammonia solution, and stir the reaction at room temperature for 1 h to obtain MIL-101@Ag seeds ( Figure 2 a); Using the seed growth method, 10 mL of 5 mg / mL glucose solution was added to the above reaction system, and the reaction was continued with stirring at room temperature for 5-30 min. MIL-101@AgNPs were obtained after centrifugation and washing.

[0037] In this example, MIL-101@AgNPs with seed growth times of 5, 15, and 30 min were prepared, and the average particle sizes of the loaded AgNPs were 47, 68, and 101 nm, respectively. Figure 2 bd). Embodiment 2:

[0038] The preparation method of the composite SERS substrate having a Raman active interface structure and an internal standard in this embodiment comprises the following specific steps: 1. Preparation of MOF materials—MIL-101 The preparation method of MIL-101 in this example is the same as that in Example 1.

[0039] 2. Preparation of MOF@PDA—MIL-101@PDA The preparation method of MIL-101@PDA in this example is the same as that in Example 1.

[0040] 3. Preparation of MOF@precious metal composite SERS substrate—MIL-101@AuNPs The MIL-101@PDA obtained in step 2 was redispersed in 20 mL of 2.5 mM chloroauric acid solution, and 200 μL of 1.0 M sodium borohydride solution was added dropwise. After stirring at room temperature for 1 h, the mixture was centrifuged and washed to obtain MIL-101@Au seeds. 1 g of polyvinyl pyrrolidone and 0.3 g of potassium iodide were dissolved in 9 mL of ultrapure water, and 1 mL of 2 M ascorbic acid and 10 mL of 50 mM chloroauric acid were added to obtain a gold growth solution. The MIL-101@Au seeds were dispersed in the gold growth solution, and the reaction was continued to stir at room temperature for 5-30 min. After centrifugation and washing, MOF@AuNPs were obtained. Embodiment 3:

[0041] The preparation method of the composite SERS substrate having a Raman active interface structure and an internal standard in this embodiment comprises the following specific steps: 1. Preparation of MOF material—UIO-66 380.6 mg of zirconium chloride and 266 mg of terephthalic acid were ultrasonically dissolved in 163.4 mL of N,N-dimethylformamide, 27.5 mL of glacial acetic acid was added, and after stirring for 2 h, the mixture was transferred to a hydrothermal reactor and reacted at 120 °C for 24 h. After cooling to room temperature, the product was washed with N,N-dimethylformamide and anhydrous ethanol three times each. Finally, the product was vacuum dried at 80 °C for 12 h to obtain UIO-66.

[0042] 2. Preparation of MOF@PDA—UIO-66@PDA 30 mg of UIO-66 material was dispersed in 20 mL of 10 mM Tris buffer, 90 mg of dopamine was added, and the reaction was stirred at room temperature for 12 h. MIL-101@PDA was obtained after centrifugation and washing.

[0043] 3. Preparation of MOF@precious metal composite SERS substrate—UIO-66@AgNPs Dissolve 0.5 g of silver nitrate in 50 mL of ultrapure water, add ammonia water dropwise until the initially generated precipitate is just dissolved to obtain a silver-ammonia solution; redisperse the UIO-66@PDA obtained in step 2 in the silver-ammonia solution, stir the reaction at room temperature for 0.5-2 h, and obtain MIL-101@AgNPs after centrifugation and washing. Embodiment 4:

[0044] The MIL-101@AgNPs composite SERS substrate prepared in Example 1 was used to detect 1-naphthol in aqueous solution, and the specific steps were as follows: 1. Using the intensity of the internal standard peak as the signal parameter, the effect of the seed growth time on the enhanced effect of the prepared MIL-101@AgNPs composite SERS substrate in Example 1 was tested. Figure 3 As shown in the figure, when the seed growth time is 30 min, the internal standard peak (1603 cm -1 ) reaches the maximum SERS intensity, indicating that the Raman hotspot structure of the composite SERS substrate can be optimized by regulating the particle size and adjacent gaps of the noble metal nanoparticles. Unless otherwise specified, the following SERS tests all use MIL-101@AgNPs with a seed growth time of 30 min as the substrate.

[0045] 2. The stability of the MIL-101@AgNPs composite SERS substrate prepared in Example 1 was tested using the intensity of the internal standard peak as the signal parameter. Figure 4 As shown, the internal standard peak (1603 cm -1 ) remained almost unchanged within 45 days, indicating that the composite SERS substrate has good stability.

[0046] 3. The concentrations of the preparations were 1.0 × 10 -6 M, 5.0 × 10 -6 M, 1.0 × 10 -5 M, 1.0 × 10 -4 M and 1.0 × 10 -3 100 μL of the above 1-naphthol solution was mixed with 900 μL of 0.2 mg / mL composite SERS substrate suspension and shaken at room temperature for 90 min. 20 μL of the resulting solution was dropped on a clean silicon wafer for Raman spectroscopy test. The results are shown in Figure 5 As shown in a, the internal standard peak (1603 cm -1 ) after normalization, the characteristic peak of 1-naphthol molecule (1062 cm -1 ) intensity increases with the increase of its concentration. -1 and 1603 cm -1 The Raman intensity ratio I 1062 / I 1603 The standard curve was obtained by taking the logarithmic concentration of 1-naphthol as the ordinate and the logarithmic concentration of 1-naphthol as the abscissa. Figure 5 b, Linear regression equation: y = 1.5804 + 0.2557 x , correlation coefficient R 2 = 0.9913).

[0047] 4. Under the same test conditions, the 1.0 × 10 -4 M 1-naphthol solution. The results are as follows Figure 6 As shown, compared with the composite SERS substrate, the single AgNPs cannot detect the signal of 1-naphthol, indicating that the prepared MIL-101@AgNPs composite SERS substrate can effectively adsorb 1-naphthol molecules that have no interaction with the noble metal nanoparticles, and utilize its Raman active interface structure to achieve SERS detection of 1-naphthol molecules.

[0048] The acquisition conditions of the Raman spectrum in this embodiment are: the excitation wavelength is 785 nm, the excitation intensity percentage is 100%, the integration time and the average number are 1600 ms and 1 respectively. Embodiment 5:

[0049] The MIL-101@AgNPs composite SERS substrate prepared in Example 1 was used to detect 1-naphthol in river water, and the specific steps were as follows: 1. Add 1-naphthol of known concentration to river water samples to make the concentrations 10, 20 and 200 μM respectively. Take 100 μL of the above river water samples and mix with 900 μL of 0.2 mg / mL composite SERS substrate suspension and shake at room temperature for 90 min. Take 20 μL of the resulting solution and drop it on a clean silicon wafer. Perform Raman spectrum test according to the Raman spectrum acquisition conditions in Example 2. At the same time, take the river water sample without 1-naphthol as a blank control. The results are shown in Figure 2. Figure 7 As shown, the SERS signal intensity is positively correlated with the content of 1-naphthol in the river water sample.

[0050] 2. Using 1-naphthol 1062 cm in Raman spectroscopy -1 and internal standard peak 1603 cm -1 The Raman intensity ratio at the locations is used as the signal parameter, and the recovery rate is 97.0%-107.5% according to the standard curve obtained in Example 2, indicating that the composite SERS substrate with a Raman active interface structure and an internal standard prepared by the present invention can be applied to the quantitative analysis of the 1-naphthol content in actual river water samples. Embodiment 6:

[0051] The MIL-101@AgNPs composite SERS substrate prepared in Example 1 was used to detect 1-naphthol in urine, and the specific steps were as follows: 1. Add 1-naphthol of known concentration to urine samples to make the concentrations 10, 20 and 200 μM respectively. Take 100 μL of the above urine samples and mix with 900 μL of 0.2 mg / mL composite SERS substrate suspension and shake at room temperature for 90 min. Take 20 μL of the resulting solution and drop it on a clean silicon wafer. Perform Raman spectrum test according to the Raman spectrum acquisition conditions in Example 2. At the same time, take the urine sample without 1-naphthol as a blank control. The results are shown in Figure 2. Figure 8 As shown, the SERS signal intensity is positively correlated with the content of 1-naphthol in the urine sample.

[0052] 2. Using 1-naphthol 1062 cm in Raman spectroscopy -1 and internal standard peak 1603 cm -1 The Raman intensity ratio at the position is used as the signal parameter, and the recovery rate is 95.0%-102.7% according to the standard curve obtained in Example 2, indicating that the composite SERS substrate with a Raman active interface structure and an internal standard prepared by the present invention can be applied to the quantitative analysis of the 1-naphthol content in actual urine samples.

[0053] The above embodiments are preferred implementation modes of the present invention, but are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a composite SERS substrate having a Raman active interface structure and an internal standard, characterized in that: Using the PDA engineering strategy, an adhesive PDA layer is formed on the MOF surface, and the noble metal nanoparticles are nucleated and grown on the surface; The MOF material is MIL-101 or UIO-66; The noble metal nanoparticles are gold nanoparticles or silver nanoparticles.

2. The preparation method according to claim 1, characterized in that The steps include: Step 1: Disperse the MOF material in Tris buffer, add dopamine, stir and react at room temperature for 12 h, centrifuge and wash to obtain MOF@PDA; Step 2: Nucleation and growth of precious metals 2a. Re-disperse the MOF@PDA obtained in step 1 in the silver ammonia solution, stir and react at room temperature for 1 h, add the glucose solution, continue to stir and react at room temperature for 5-30 min, centrifuge and wash to obtain MOF@AgNPs; 2b. Re-disperse the MOF@PDA obtained in step 1 in chloroauric acid solution, add sodium borohydride solution dropwise, stir and react at room temperature for 1 h, centrifuge and wash, and then disperse it in gold growth solution again, continue to stir and react at room temperature for 5-30 min, centrifuge and wash to obtain MOF@AuNPs.

3. The preparation method according to claim 2, characterized in that: In step 1, the pH of the Tris buffer is 8.

5.

4. The preparation method according to claim 2, characterized in that: In step 2a, the silver ammonia solution is prepared by dissolving 0.5 g of silver nitrate in 50 mL of ultrapure water, and adding ammonia water dropwise until the initially generated precipitate is just dissolved, thereby obtaining the silver ammonia solution.

5. The preparation method according to claim 2, characterized in that: In step 2b, the gold growth solution is prepared by dissolving 1 g of polyvinyl pyrrolidone and 0.3 g of potassium iodide in 9 mL of ultrapure water, and adding 1 mL of 2 M ascorbic acid and 10 mL of 50 mM chloroauric acid to obtain the gold growth solution.

6. Use of the composite SERS substrate having a Raman active interface structure and an internal standard prepared by the preparation method according to any one of claims 1 to 5 in the detection of phenolic compounds.

7. The use according to claim 6, characterized in that: The phenolic compound is 1-naphthol or 2-naphthol.

8. The use according to claim 6, characterized in that: The relative intensities of the characteristic peaks of phenolic compounds and the internal standard peaks are used as signal parameters to achieve quantitative detection of phenolic compounds in the sample to be tested.

9. The use according to claim 8, characterized in that: The sample to be tested is a liquid, including a water sample or a biological sample.

10. The use according to claim 8, characterized in that: Prepare 1.0 × 10 -6 M to 1.0 × 10 -3 100 μL of the aqueous solutions of phenolic compounds with different concentrations in the range of M were taken and mixed with 900 μL of 0.2 mg / mL composite SERS substrate suspension and shaken at room temperature for 90 min. 20 μL of the obtained solution was dropped on a silicon wafer for Raman spectroscopy test. The Raman spectrum at 1062 cm -1 and 1603 cm -1 The Raman intensity ratio I 1062 / I 1603 The standard curve is obtained with the logarithmic concentration of phenolic compounds as the vertical coordinate and used for the quantitative detection of phenolic compounds in the samples to be tested.

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