Preparation method of SERS substrate for organophosphorus compound

Abstract

The invention discloses a preparation method of an SERS (Surface Enhanced Raman Scattering) substrate for organophosphorus compounds, which realizes rapid and sensitive detection of the organophosphorus compounds A hydrothermal method is used for synthesizing gold / silver nanoparticles, and the gold / silver nanoparticles are fixed on a gold film by adopting a physical sedimentation method to construct a periodic and uniform substrate. Different metal single atom solutions are prepared, metal single atoms are loaded on a gold / silver substrate, and single atom sites form an SERS enhanced area, so that adsorption of an organic phosphorus compound on the surface of the substrate is promoted, and sensitivity and repeatability of detection of the organic phosphorus compound are realized. The preparation method of the substrate is simple and convenient to operate and high in sensitivity and repeatability, and has good application in the aspect of organophosphorus compound detection.

Description

Technical Field

[0001] This invention relates to the field of analytical detection, and more specifically to a method for preparing SERS substrates suitable for organophosphorus compounds such as dimethyl methylphosphonate, malathion, diethyl cyanophosphonate, chlorpyrifos, and glyphosate. Background Technology

[0002] Organophosphorus compounds are diverse and highly toxic, and widely used in daily life. In agriculture, organophosphorus pesticides (such as chlorpyrifos, glyphosate, and dimethoate) are commonly used to control pests and weeds. However, pesticide residues can harm the environment and enter the human body through the food chain, seriously endangering human health. Therefore, achieving rapid and sensitive detection of nerve agents is of great significance to human health and national security. Currently, detection methods for organophosphorus compounds include GC-MS, LC-MS, immunoassay, and electrochemical methods. These methods are highly sensitive and accurate, but they have drawbacks such as long processing times, the need for professional operators, and sensitivity to environmental factors, failing to meet the requirements for rapid and sensitive detection. Theoretically, SERS technology can achieve single-molecule detection through the SPR phenomenon of noble metal nanostructures. However, due to the low polarity, volatility, and weak affinity for metals of organophosphorus compounds, the SERS detection of organophosphorus compounds faces challenges.

[0003] The enhancement of SERS primarily originates from two mechanisms: electromagnetic enhancement and chemical enhancement. Electromagnetic enhancement is related to the surface plasmon resonance effect of metal nanostructures, while chemical enhancement involves chemical interactions between molecules and the metal surface, such as charge transfer. Metal single atoms, due to their unique electron orbital distribution, possess excellent electron-accepting capabilities, such as in Ni. 2+ The d orbitals of the molecule may interact with the Fermi level of the metal, promoting molecule-metal charge transfer under laser excitation and significantly amplifying the Raman signal of the molecule. Bipyridine compounds can form stable complexes with metal ions such as ruthenium, palladium, nickel, and copper. The nitrogen atom or aromatic ring of bipyridine readily adsorbs onto the metal surface, and the N atom readily forms interactive hydrogen bonds with other molecules, promoting the adsorption of the analyte molecule, reducing the distance between the molecule and the metal, and bringing the molecule closer to the hot spot region, which is beneficial for electromagnetic enhancement. Summary of the Invention

[0004] In view of this, the main objective of this invention is to provide a method for preparing a SERS chip with loaded metal sites and its application in the detection of nerve agent target molecules, thereby solving the aforementioned technical problems. To achieve this objective, as one aspect of this invention, a method for preparing a regular and uniform Au / Ag substrate is provided. Through a charge transfer mechanism between metal and molecules, organophosphorus compounds are introduced into the SERS-enhanced hotspot region of the gold / silver nanoaggregates. Under optimal conditions of molar ratio, laser wavelength, integration time, and laser power, qualitative and quantitative analysis of dimethyl methylphosphonate, diethyl cyanophosphate, malathion, chlorpyrifos, and glyphosate is achieved.

[0005] The present invention adopts the following technical solution:

[0006] (1) Gold or silver nanoparticle sol was prepared by hydrothermal synthesis of trisodium citrate and then fabricated into gold / silver substrate chip.

[0007] (2) Load metal single atoms onto a gold / silver substrate chip, select the compound corresponding to the metal single atom, separate each metal atom through coordination or steric hindrance effect, and use drop coating to load the compound corresponding to the metal single atom onto the gold / silver substrate, thereby enabling the metal site, i.e. the metal single atom, to be loaded onto the gold or silver substrate chip, and finally forming a SERS substrate.

[0008] In step (1), silver nitrate solution is added to the container, heated to boiling in a water bath, trisodium citrate solution is added, and the reaction is continued to obtain silver nanoparticle sol; the particle size of the prepared silver nanoparticles is 30±10nm.

[0009] Alternatively, in step (1), deionized water is added to the container, followed by sodium citrate solid. The mixture is heated to boiling in a water bath, then chloroauric acid solution is added, and the reaction is continued to obtain a gold nanoparticle sol. The prepared gold nanoparticles have a particle size of 20±5 nm.

[0010] The gold / silver substrate is prepared by immersing a gold-plated silicon wafer in a synthesized gold or silver nanoparticle sol and allowing it to stand. Afterward, it is removed and dried in a vacuum drying oven at 50–60°C, forming a uniform and evenly distributed array structure of gold / silver nanoparticles.

[0011] Step (2) The compound corresponding to the metal single atom is selected from nickel bipyridine dichloride, ruthenium tripyridine chloride, copper bipyridine, palladium bipyridine dichloride, nickel chloride, ruthenium trichloride, copper chloride, palladium chloride, nickel hydroxide, nickel sulfate, palladium hydroxide, copper sulfate, etc.; the compound corresponding to the metal single atom is dispersed in an organic solvent and then coated onto a gold / silver substrate chip, the concentration of the compound corresponding to the metal single atom is 10. -2 ~10 -4 M.

[0012] The prepared SERS substrate is denoted as forming AB chip, where A corresponds to nickel, copper, palladium, ruthenium, etc.; and B corresponds to Au, Ag.

[0013] Application: The organophosphorus compounds to be tested are dropped onto a SERS substrate chip. Surface-enhanced Raman scattering (SERS) is performed on the chip at the corresponding optimal excitation wavelength. By measuring the Raman peak intensity of dimethyl methylphosphonate, malathion, diethyl cyanophosphate, chlorpyrifos, and glyphosate at specific wavelengths, the analysis and detection of several organophosphorus compounds can be achieved. The mass concentration of the sample solution is 10. 2 ~10 6 ng / L.

[0014] The optimal excitation wavelength was 785 nm. The organophosphorus compounds to be tested were dropped onto a SERS substrate chip for continuous spectral acquisition. The mass concentrations of dimethyl methylphosphonate, malathion, and diethyl cyanophosphate were 100 ppm, and the mass concentrations of chlorpyrifos and glyphosate were 1 ppm.

[0015] In step (2) of this invention, a metal single atom refers to the active site of a metal pair existing in the form of isolated atomic dispersion, which improves the utilization rate of metals and avoids the formation of clusters between metal elements. Usually, these metal atoms need to be "anchored" or "fixed" through strong chemical interactions.

[0016] Compared with the prior art, the beneficial effects achieved by the technical solution of this invention are:

[0017] 1. This invention relates to a detection technology for organophosphorus compounds. Utilizing the unique electronic orbitals of single atoms, charge transfer occurs between the single atom, the organophosphorus compound, and the metal under laser irradiation, promoting the polarization of groups such as P=O and creating a SERS-enhanced region. This enhances and amplifies the Raman signal of organophosphorus compounds adsorbed on the surface of silver nanoparticles, thereby achieving qualitative analysis of organophosphorus compounds. The qualitative analysis and detection of organophosphorus compounds involves dropping a sample solution onto a prepared chip, performing surface-enhanced Raman detection at the optimal excitation wavelength, laser power, and integration time, and comparing the Raman peak of the sample with that of a standard.

[0018] 2. Dimethyl methylphosphonate, malathion, diethyl cyanophosphonate, chlorpyrifos, and glyphosate exhibit different SERS characteristic peaks. These five compounds can be distinguished based on their different SERS characteristic peaks. The Raman characteristic peak of dimethyl methylphosphonate is at 710 cm⁻¹. -1 It is generated by CP bond vibration; the Raman characteristic peak of malathion is at 635 cm⁻¹. -1 The peak is generated by the P=S bond vibration; the Raman characteristic peak of diethyl cyanophosphonate is at 759 cm⁻¹. -1The Raman characteristic peaks of chlorpyrifos and glyphosate are generated by OPO vibration; the Raman characteristic peaks of chlorpyrifos and glyphosate are at 1310 cm⁻¹. -1 It is generated by the vibration of P=O and P=S groups.

[0019] This invention relates to the preparation of gold / silver nanoparticles based on the hydrothermal synthesis of trisodium citrate. A uniform gold / silver array is prepared by physical deposition and vacuum drying. The array surface is modified with metal single atoms. The SERS substrate has the advantages of simple synthesis, high sensitivity and good reproducibility. It is a qualitative analysis method that can directly use the SERS characteristic peaks of the sample solution. Attached Figure Description

[0020] Figure 1 Images (a) and (b) are SEM images of a periodic, regular, and uniform silver substrate, while images (c) and (d) are SEM images of the SERS chip containing bipyridine molecular sites.

[0021] Figure 2 HAADF-STEM image of silver sol

[0022] Figure 3 These are SERS spectra of four single-atom sites of malathion, at 535 cm⁻¹. -1 Bar chart of peak intensity contrast

[0023] Figure 4 These are SERS spectra of four single-atom site dimethyl methylphosphonate, at 710 cm⁻¹. -1 Bar chart of peak intensity contrast

[0024] Figure 5 These are SERS spectra of four single-atom sites of diethyl p-cyanophosphonate, at 759 cm⁻¹. -1 Bar chart of peak intensity contrast

[0025] Figure 6 This is the SERS spectrum of single-atom sites for chlorpyrifos and glyphosate.

[0026] Figure 7 SERS waterfall plots of multiple parallel measurements of malathion, dimethyl methylphosphonate, and diethyl cyanophosphonate Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0028] This invention discloses a method for preparing an organophosphorus compound surface-enhanced Raman scattering (SERS) substrate. The method involves first synthesizing a gold or silver nanoparticle sol, immobilizing the gold or silver nanoparticles on a silicon-based gold film, and then loading metal single atoms onto the gold / silver substrate. By determining the characteristic peak positions and intensities of the SERS peaks, the analytical detection of the sample can be achieved.

[0029] Example 1:

[0030] Preparation method of silver sol: Take 100mL of silver nitrate solution into a single-necked round-bottom flask, stir magnetically in a water bath, heat to boiling, add the prepared trisodium citrate solution, continue heating for 20-30 minutes until the color turns grayish-green, stop heating, cool naturally, and store away from light.

[0031] This invention allows for the preparation of silver nanoparticles with uniform particle size by controlling the concentration of sodium citrate, reaction temperature, and reaction time. The sodium citrate solution has a mass percentage concentration of 5%, the silver nitrate solution has a concentration of 1 mM, and the volume ratio of sodium citrate solution to silver nitrate solution is 50:1. The stirring speed is 400–600 r / min; the reaction temperature is 90–100 °C.

[0032] The synthesized silver sol was centrifuged at 7500 rpm for 5 minutes. After centrifugation, the supernatant was removed, ethanol solution was added, and the mixture was centrifuged again. The supernatant was removed, and the mixture was resuspended in pure water. Gold-plated silicon wafers, cut into regular 5mm × 5mm squares, were ultrasonically cleaned three times alternately with water and ethanol, and then vacuum-dried at 60℃. The gold-plated silicon wafers were then placed in the sol and allowed to stand for different periods.

[0033] Figure 1 These are SEM characterization images, showing that the particles have fallen onto the silicon wafer. The surface density of the nanoparticles can be controlled by adjusting the deposition time. Images (a) and (b) show the optimized density. With a deposition time of 3 hours, the particles are evenly distributed and have a moderate thickness.

[0034] Figure 2 Is TEM-HAADF such as Figure 2 Characterization diagram shows that the synthesized silver nanoparticles are approximately 30 nm in size.

[0035] Example 2:

[0036] Preparation method of gold sol: Place 100 mL of deionized water in a three-necked flask and place it in a constant temperature water bath. Add 0.097 g of sodium citrate to the water quantitatively and dissolve it completely with continuous stirring. When the system temperature stabilizes at 95-100℃, add 1 mL of 0.98% HAuCl4·3H2O solution dropwise, while increasing the stirring speed to 1000 r / min to ensure rapid mixing.

[0037] Example 3:

[0038] Preparation method of single-atom metal compounds loaded on gold / silver Ag substrates: Solutions of bipyridine nickel chloride, tripyridine ruthenium chloride, bipyridine copper, bipyridine palladium chloride, nickel chloride, ruthenium trichloride, copper chloride, palladium chloride, nickel hydroxide, nickel sulfate, palladium hydroxide, and copper sulfate at different concentrations were prepared using dimethyl sulfoxide at a concentration of 10%. -2 ~10 -4 M. The gold / silver substrate prepared in Example 1 or 2 is immersed in different single-atom metal compounds and left to stand for a period of time, such as 6 hours. After that, the chip is taken out, rinsed with pure water, and air-dried.

[0039] Figure 1 Figures (c) and (d) show the site chip with single atoms loaded. The regions loaded with single atoms form aggregates, which is conducive to the formation of hot spots and the adsorption of analyte molecules.

[0040] Example 4:

[0041] Malathion SERS detection: A standard solution of malathion was prepared and diluted to 100 ppm using methanol as the solvent. The Raman spectrometer parameters were set as follows: excitation wavelength 785 nm, laser power 50 mW, integration times 1, integration time 1 s. The Raman spectrometer was calibrated using a silicon wafer, with a characteristic peak shift of 520.6 cm⁻¹. -1 The Raman peak intensity of the silicon wafer was 5000. The prepared chip was then placed under a Raman spectrometer. The video screen was observed, the focus was adjusted, and 10 μl of diluted malathion solution was dropped onto the chip using a pipette. Continuous spectral acquisition was then performed, and the 535 cm⁻¹ peak intensity was observed. -1 The peak value at that location changes.

[0042] Figure 3 Four SERS enhancement effects of single-atom malathion were presented. According to the bar chart, it can be seen that the chip prepared with bipyridine nickel chloride as the single-atom solution (the corresponding gold or silver substrate can be used) is the optimal chip for malathion testing. The SERS peak intensity of 100 ppm malathion solution can reach 8000.

[0043] Example 5:

[0044] SERS detection of dimethyl methylphosphonate: A standard solution of dimethyl methylphosphonate was prepared and diluted to 100 ppm using methanol as the solvent. The Raman spectrometer parameters were set as follows: excitation wavelength 785 nm, laser power 30 mW, integration times 1, integration time 1 s. The Raman spectrometer was calibrated using a silicon wafer, with a characteristic peak shift of 520.6 cm⁻¹. -1The Raman peak intensity of the silicon wafer was 5000. The prepared chip was then placed under a Raman spectrometer. The video screen was observed, the focus was adjusted, and 10 μl of diluted dimethyl methylphosphonate solution was dropped onto the chip using a pipette. Continuous spectral acquisition was then performed, and the 710 cm⁻¹ peak intensity was observed. -1 The peak value at that location changes.

[0045] Figure 4 Four single-atom SERS enhancement effects on dimethyl methylphosphonate were presented. According to the bar chart, it can be seen that the optimal chip for SERS detection of dimethyl methylphosphonate is the Ni-Au chip (with gold as the bottom layer and Ni single atoms as the top layer), and the SERS peak intensity of a 100ppm dimethyl methylphosphonate solution can reach 4000.

[0046] Example 6:

[0047] SERS detection of diethyl cyanophosphonate: A standard solution of diethyl cyanophosphonate was prepared and diluted to 100 ppm using methanol as the solvent. The Raman spectrometer parameters were set as follows: excitation wavelength 785 nm, laser power 50 mW, integration times 1, integration time 1 s. The Raman spectrometer was calibrated using a silicon wafer, with a characteristic peak shift of 520.6 cm⁻¹. -1 The Raman peak intensity of the silicon wafer was 5000. The prepared chip was then placed under a Raman spectrometer. The video screen was observed, the focus was adjusted, and 10 μl of diluted diethyl cyanophosphonate solution was dropped onto the chip using a pipette. Continuous spectral acquisition was then performed, and the 759 cm⁻¹ peak intensity was observed. -1 The peak value at that location changes.

[0048] Figure 5 The SERS enhancement effects of four single-atom p-cyanophosphonate diethyl esters were presented. According to the bar chart, it can be seen that the optimal chip for SERS detection of cyanophosphonate diethyl ester is the Pd-Ag chip (Ag bottom layer and Pd single atoms top layer), and the SERS peak intensity of 100ppm cyanophosphonate diethyl ester solution can reach 5500.

[0049] Example 7:

[0050] SERS detection of chlorpyrifos and glyphosate: 10 mg of chlorpyrifos solid and 10 mg of glyphosate solid were respectively used as solvent to prepare chlorpyrifos solution and glyphosate solution with a mass concentration of 1 ppm using methanol. The Raman spectrometer parameters were set as follows: excitation wavelength 785 nm, laser power 50 mW, integration times 1, integration time 1 s. The Raman spectrometer was calibrated using a silicon wafer, and the characteristic peak shift of the silicon wafer was 520.6 cm⁻¹. -1The Raman peak intensity of the silicon wafer was 5000. The prepared chip was then placed under a Raman spectrometer. The video screen was observed, the focus was adjusted, and 10 μl of diluted chlorpyrifos and glyphosate solutions were respectively dropped onto the chip using a pipette. Continuous spectral acquisition was then performed, and the image was observed at 1310 cm⁻¹. -1 The peak value changes at the specified location. The optimal substrate for organophosphorus pesticides is a Ni-Au substrate (Au as the bottom layer and Ni single atoms as the top layer). According to Raman spectroscopy results, the SERS peak intensity of a 1 ppm chlorpyrifos solution can reach 2000, and the SERS peak intensity of a 1 ppm glyphosate solution can reach 4000.

[0051] Figure 6 The results are from Example 5, namely the SERS spectra of chlorpyrifos and glyphosate.

[0052] Example 8:

[0053] Repeatability testing:

[0054] 10 μl of 100 ppm diethyl cyanophosphonate, dimethyl methylphosphonate, and malathion solutions were dropped onto Pd-Ag, Ni-Ag, and Ni-Au chips, respectively. After natural drying, Raman spectra were collected with a laser power of 50 mW and an integration time of 1 s.

[0055] Figure 7 The results are from Example 6, which shows multiple parallel measurements of the SERS spectra of malathion, dimethyl methylphosphonate, and diethyl cyanosulfate. The characteristic peak positions for each molecule are consistent, the signal intensity is uniformly distributed along the Y-axis, and the peak shape shows no significant changes, indicating good reproducibility of the SERS substrate and its applicability to the qualitative analysis of organophosphorus compounds using SERS.

Claims

1. A method for preparing a SERS substrate for an organophosphorus compound, characterized by, The method comprises the following steps: (1) preparing gold or silver nano-particle sol by using the trisodium citrate hydrothermal synthesis method, and then preparing a gold / silver substrate chip; (2) loading metal monatomic atoms on the gold / silver substrate chip, selecting a compound corresponding to the metal monatomic atoms, separating each metal atom by coordination or steric hindrance effect, loading the compound corresponding to the metal monatomic atoms on the gold / silver substrate by using the drop coating method, and then loading the metal sites, i.e. the metal monatomic atoms, on the gold or silver substrate chip, and finally forming a SERS substrate.

2. The method for preparing a SERS substrate for organic phosphorus compounds according to claim 1, characterized by, In step (1), silver nitrate solution is added to a container, heated to boiling in a water bath, and then trisodium citrate solution is added, and the reaction is continued to obtain silver nano-particle sol; the prepared silver nano-particle has a particle size of 30±10 nm. In step (1), deionized water is added to a container, and then sodium citrate solid is added, heated to boiling in a water bath, and then chloroauric acid solution is added, and the reaction is continued to obtain gold nano-particle sol. The prepared gold nano-particle has a particle size of 20±5 nm.

3. The method for preparing a SERS substrate for organophosphorus compounds according to claim 1, characterized by, The gold / silver substrate is prepared by immersing the gold-plated silicon wafer in the prepared gold or silver nano-particle sol, and then taking it out and drying it in a vacuum drying oven at a temperature of 50-60°C; a uniform and full array structure of gold / silver nano-particles is formed.

4. The method for preparing a SERS substrate for organic phosphorus compounds according to claim 1, characterized by, Step (2) the compound corresponding to the metal monatomic is selected from nickel dipyridyl dichloride, trispyridine ruthenium chloride, copper dipyridyl, palladium dipyridyl dichloride, nickel chloride, ruthenium trichloride, copper chloride, palladium chloride, nickel hydroxide, nickel sulfate, palladium hydroxide, copper sulfate and the like; the compound corresponding to the metal monatomic is dispersed in an organic solvent, and then coated on a gold / silver substrate chip, the concentration of the compound corresponding to the metal monatomic is 10 -2 ~ 10 -4 M.

5. The SERS substrate prepared by the method according to any one of claims 1-4 is denoted as A-B chip, A corresponds to nickel, copper, palladium, ruthenium, etc.; and B corresponds to Au and Ag.

6. The SERS substrate prepared by the method according to any one of claims 1-4 is used for detection of organic phosphorus compounds, including qualitative and quantitative analysis and detection of dimethyl methylphosphonate, diethyl cyanophosphonate, malathion, chlorpyrifos and glyphosate.

7. Use according to claim 6, characterized in that, The organic phosphorus compound to be detected is dropped on the SERS substrate chip, and the chip is subjected to surface-enhanced Raman scattering detection under the corresponding optimal excitation wavelength, and the Raman peak intensity of dimethyl methylphosphonate, malathion, diethyl cyanophosphonate, chlorpyrifos and glyphosate at a specific wavelength is measured to realize analysis and detection of several organic phosphorus compounds.

8. Use according to claim 7, characterized in that, The optimal excitation wavelength is 785 nm, the organic phosphorus compound to be detected is dropped on the SERS substrate chip, and continuous spectrum sampling is performed. The mass concentration of dimethyl methylphosphonate, malathion and diethyl cyanophosphonate is 100 ppm, and the mass concentration of chlorpyrifos and glyphosate is 1 ppm.

9. Use according to claim 7, characterized in that, The chip for SERS detection of dimethyl methylphosphonate is a Ni-Au chip; the chip for SERS detection of diethyl cyanophosphonate is a Pd-Ag chip; and the substrate for organic phosphorus pesticide is a Ni-Au chip.

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