A simplified method for preparing sers nanoparticles and its application in pesticide residue detection

Abstract

The application discloses a simplified SERS nanoparticle preparation method and application in pesticide residue detection, and belongs to the technical field of spectral analysis and detection. The preparation method comprises the following steps: taking gold nanoparticles as initial nanoparticles, then reducing AgNO3 under alkaline conditions by using beta-CD, so as to form Au-Ag Janus. The beneficial effects are as follows: the beta-CD modified silver-coated gold nanoparticles are Janus structure, the size of which can be adjusted according to requirements; the beta-CD comprises a hydrophobic inner cavity and a hydrophilic outline, so that hydrophobic organic small molecules can be captured in the cavity and stable host-guest inclusion compounds are formed, macromolecular recognition is realized, and the detection sensitivity of SERS is greatly improved. The preparation method of the Au-Ag Janus nano material is simple, fast, stable, reproducible and high in sensitivity, and the SERS detection method adopted is simple and fast.

Description

Technical Field

[0001] This invention belongs to the field of spectroscopic analysis and detection technology, specifically relating to a simplified method for preparing Au-Ag Janus nanomaterials and their application in pesticide residue detection. Background Technology

[0002] Pesticides are a special class of chemicals that, while controlling agricultural and forestry pests and diseases, can also harm humans and livestock, damaging the environment upon which humanity depends. According to literature, pesticide utilization rates are generally only 10%, with approximately 90% remaining in the environment, causing pollution. Large amounts of pesticides evaporate into the air, flow into water bodies, and accumulate in the soil, contaminating agricultural, livestock, and fruit products. They can also be transferred to humans through bioaccumulation in the food chain, posing a health risk. Pesticide residue problems exist to varying degrees in countries worldwide. For example, consuming food containing high levels of highly toxic pesticide residues can lead to acute poisoning in humans and livestock. The irrational use of pesticides, especially herbicides, results in frequent pesticide damage incidents, often causing large-scale yield reductions or even crop failures, severely impacting agricultural production. Excessive pesticide use damages the ecological environment, causing pollution; high residue levels have adverse effects on human health, causing not only acute poisoning but also teratogenic, carcinogenic, and mutagenic effects.

[0003] From an environmental protection perspective, rapid, convenient, and specific detection of pesticide residues in environmental samples is both necessary and urgent. Developing rapid detection methods and tools for various agrochemicals such as pesticides, fungicides, and herbicides in food is crucial. While traditional chromatography and gas chromatography-tandem mass spectrometry offer high detection accuracy, they suffer from drawbacks such as expensive instruments, complex operating systems, long measurement times, and sample degradation.

[0004] Surface-enhanced Raman spectroscopy (SERS) has attracted widespread attention due to its advantages of being fast, sensitive, non-destructive, and capable of detecting trace amounts. However, this technique is highly dependent on nanoparticles; if the nanoparticles are not uniform, it will lead to signal instability and poor repeatability. Therefore, the preparation of uniform and stable SERS-active nanomaterials is the key problem addressed in this invention.

[0005] Chinese patent application CN115825039A discloses a method for detecting pyrene based on β-cyclodextrin-modified silver nanoparticles and surface-enhanced Raman spectroscopy (SERS). The method includes mixing a solution with a sodium citrate solution and heating it until it changes from colorless to yellow-green to obtain a silver nanoparticle solution. The prepared silver nanoparticles are then mixed with mercapto-β-cyclodextrin, kept at a constant temperature and shaken overnight, and stored in the dark for later use. This method can be used to detect pyrene in the environment. However, the silver nanoparticles prepared by this patent are not uniform and stable enough, making them insufficiently sensitive as a SERS substrate for detecting pyrene, and their use for detecting pesticides is not disclosed.

[0006] A review of the literature revealed that the method proposed in the article "Lu,Y.;Yao,G.;Sun,K.;Huang,Q.,beta-Cyclodextrin coatedSiO2@Au@Ag core-shell nanoparticles for SERS detection of PCBs. PHYSICALCHEMISTRY CHEMICAL PHYSICS 2015,17(33),21149-21157." is to reduce silver on SiO2@Au nanoparticles with β-CD to prepare SiO2@Au nanoparticles. Although the prepared SiO2@Au@Ag nanoparticles have a more uniform morphology, the steps are relatively complicated, time-consuming, and have a short storage time. Summary of the Invention

[0007] The technical problem to be solved by this invention is how to solve the problems of poor stability and low reproducibility of existing SERS detection signals, thereby realizing the task of highly sensitive and rapid on-site detection of various pesticides.

[0008] The present invention solves the above-mentioned technical problems through the following technical means:

[0009] The first aspect of this invention provides a simplified method for preparing Au-Ag Janus nanomaterials, comprising the following steps:

[0010] (1) A solution of gold nanoparticles (AuNPs) was prepared by hydrothermal reduction.

[0011] (2) Using the gold nanoparticle solution obtained in step (1) as a precursor, AgNO3 is reduced with β-cyclodextrin under alkaline conditions to form Au-Ag Janus.

[0012] Beneficial effects: The β-CD modified silver-coated gold nanoparticles prepared by the technical solution of this invention have a Janus structure, and their size can be adjusted as needed. β-CD contains a hydrophobic cavity and a hydrophilic profile, thus it can capture hydrophobic small organic molecules in the cavity and form stable host-guest inclusion complexes, achieving polymer recognition. This greatly improves the detection sensitivity of SERS.

[0013] Preferably, the specific preparation method of gold nanoparticles in step (1) includes the following steps:

[0014] A. Prepare an aqueous solution of chloroauric acid, store it at 4°C protected from light, and use it for later use;

[0015] B. Place ultrapure water in a reactor, add a magnetic wave, place it in an oil bath, and heat and stir until boiling.

[0016] C. Add the aged chloroauric acid aqueous solution to water, add the reducing agent solution, and continue heating and stirring until the solution changes from colorless to wine red.

[0017] D. Stop heating and continue stirring while cooling;

[0018] E. Store in the refrigerator for later use.

[0019] Preferably, the preparation method of Au-Ag Janus in step (2) includes the following steps:

[0020] a. Place the prepared gold nanoparticle solution into a centrifuge and centrifuge;

[0021] b. Discard the supernatant, add ultrapure water to redissolve the nanoparticles, and place them in an ultrasonic machine to disperse the nanoparticles evenly.

[0022] c. Take the reducing agent β-cyclodextrin (β-CD) powder and gold nanoparticle solution, add them to ultrapure water, and place them in an oil bath for stirring and heating;

[0023] d. Add alkaline solution to adjust the pH of the reaction system while stirring;

[0024] e. Add AgNO3 solution to the reaction system and continue heating and stirring;

[0025] f. Allow the nanoparticles to cool naturally to room temperature, then centrifuge and wash them for later use.

[0026] Preferably, the reducing agent in step C is sodium citrate.

[0027] Preferably, the alkaline solution in step d is an aqueous solution of NaOH.

[0028] Preferably, in step c, the temperature is heated to 95-98°C.

[0029] Preferably, the stirring time in step e is 30-40 minutes.

[0030] A second aspect of the present invention provides a simplified Au-Ag Janus nanomaterial prepared by the above method.

[0031] A third aspect of the present invention proposes the application of the above-mentioned SERS substrate in pesticide residue detection.

[0032] Preferably, the pesticide includes, but is not limited to, one or more of thiram, paraquat, and carbendazim.

[0033] The advantages of this invention are:

[0034] 1. The technical solution of this invention prepares β-CD modified silver-coated gold nanoparticles with a Janus structure, the size of which can be adjusted as needed. β-CD contains a hydrophobic cavity and a hydrophilic profile, thus it can capture hydrophobic small organic molecules in the cavity and form stable host-guest inclusion complexes, achieving polymer recognition. This greatly improves the detection sensitivity of SERS.

[0035] 2. The SERS substrate preparation process in this invention is simple and rapid, resulting in a substrate with good stability, resistance to oxidation, and the ability to be stored at room temperature for extended periods while maintaining a certain SERS enhancement capacity. The substrate can be prepared at any time for testing, making it convenient and quick.

[0036] 3. This patent utilizes a simplified method to prepare β-CD-modified silver-coated gold nanoparticles. The preparation method is optimized for controlling the nanoparticle morphology, resulting in more uniform nanoparticle size and morphology, greater stability in conventional environments, longer shelf life, and improved measurement signals. This method can be widely applied to pesticide residue detection.

[0037] 4. This invention proposes a simpler and more effective method for preparing uniform nanoparticles with SERS activity. The prepared β-CD-modified Au-Ag Janus nanoparticles are uniform in size and morphology, and exhibit excellent physical and chemical stability, allowing for long-term storage under normal environmental conditions. Utilizing their excellent SERS activity and high adsorption capacity for pesticides, they can be widely used for the detection of various pesticide residues. Attached Figure Description

[0038] Figure 1 A 3D image of a single Au-Ag Janus particle prepared in Example 1 of this invention;

[0039] Figure 2 The image shows the SERS spectra of different concentrations of thiram detected in Example 2, and the image at 1376 cm⁻¹. -1 The relationship between SERS intensity and concentration of different concentrations of thiram is shown in the figure.

[0040] Figure 3 for Figure 4 The SERS spectra of different concentrations of paraquat were detected in Example 3, and the SERS spectra at 1192 cm⁻¹ were obtained. -1 The graph shows the relationship between the SERS intensity of different concentrations of paraquat and its concentration.

[0041] Figure 4 The image shows the SERS spectra of different concentrations of carbendazim detected in Example 4, and the values ​​at 1268 cm⁻¹. -1 The relationship between SERS intensity and concentration of different concentrations of carbendazim is shown in the figure.

[0042] Figure 5 The image shows the SERS spectra of different concentrations of thiram on the skin of fruits and vegetables in Example 5.

[0043] Figure 6 The image shows the SERS spectra of different concentrations of paraquat on the skin of fruits and vegetables in Example 6.

[0044] Figure 7 The above are SERS spectra of different concentrations of carbendazim detected on the surface of fruits and vegetables in Example 7.

[0045] Figure 8 The SERS substrate prepared in Example 1 had a detection concentration of 10. -14 SERS spectrum of M-ATP. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] Example 1:

[0048] This embodiment discloses a simplified method for preparing Au-Ag Janus nanomaterials, the specific steps of which are as follows:

[0049] (1) Preparation of gold nanoparticle (AuNPs) solution by hydrothermal reduction method

[0050] The gold nanoparticle solution was prepared by modifying the method described by Frens, and its synthesis method is based on the literature (G. Frens. Controlled Nucleation for the Regulation of the Regulation of the Particle Size in Monodisperse Gold Supplements. [J]. Nature Physical Science, 1973, 241, 20-22). In this embodiment, gold nanoparticles with a size of 20 nm were obtained by adjusting the synthesis conditions.

[0051] The preparation process of the gold nanoparticles is as follows: A. Dissolve an aqueous solution of chloroauric acid in ultrapure water to obtain an aqueous solution of chloroauric acid, and let the aqueous solution stand at 4°C in the dark. B. Place ultrapure water in an Erlenmeyer flask, add a magnetic stir bar, and heat in an oil bath until boiling. C. Add the aqueous solution of chloroauric acid prepared in A and an aqueous solution of sodium citrate, and continue heating and stirring until the color changes from colorless to wine red. D. Stop heating and continue stirring until room temperature. E. Store the solution in a refrigerator at 4°C for later use.

[0052] (2) The specific preparation method of Au-Ag Janus is as follows:

[0053] a. Take the gold nanoparticle solution obtained in step (1) and centrifuge it; b. Remove the supernatant of the centrifuged solution, add the same volume of aqueous solution, and aspirate it several times with a pipette tip to initially disperse the nanoparticles into the aqueous solution. Then, place the centrifuge tube in an ultrasonic machine and sonicate it to disperse the nanoparticles evenly; c. Take β-CD powder, the washed gold nanoparticle solution, and ultrapure water into an Erlenmeyer flask, place it in an oil bath, heat it to 95-98℃, and stir; d. Add NaOH solution to adjust the pH of the solution; e. Add AgNO3 solution and continue heating and stirring for 30-40 minutes; let the nanoparticles cool naturally to room temperature, and then centrifuge and wash them for later use.

[0054] The simplified Au-Ag Janus nanomaterials prepared above were used as SERS substrates for the detection of pesticide residues.

[0055] Example 2:

[0056] Prepare pesticide solution standards of different concentrations. Place the standard solution in a test bottle, add Au-Ag Janus nanoparticle solution, and then add NaCl solution, mixing thoroughly. Place aluminum foil on a glass slide and drop pesticide standards of different concentrations onto it. Allow the liquid standards to air dry at room temperature. Perform SERS detection using a Raman spectrometer. Figure 2The SERS spectra of different concentrations of thiram are shown; analysis of its characteristic Raman peak at 1376 cm⁻¹ is performed. -1 The peak intensity was obtained, and the Raman signal of the thiamethoxam with concentration was measured at 1376 cm⁻¹. -1 The graph shows the SERS intensity of thiram at different concentrations as a function of concentration. It can be seen that the higher the concentration of thiram, the stronger its SERS intensity at 1376 cm⁻¹. -1 The greater the SERS intensity at a given location, the better for achieving trace detection and analysis of fosetyl-Al.

[0057] Example 3:

[0058] The preparation of the SERS substrate in this embodiment is the same as in Example 1. The SERS substrate obtained in this embodiment is used for the detection of paraquat aqueous solution, and the operation steps are the same as in Example 1. The experimental results of this embodiment are as follows. Figure 3 As shown, the SERS spectra of different concentrations of paraquat in this embodiment and the SERS spectra at 1192 cm⁻¹ are presented. -1 The graph shows the relationship between the SERS intensity of paraquat at different concentrations and its concentration.

[0059] Example 4:

[0060] The preparation of the SERS substrate in this embodiment is the same as in Example 1. The SERS substrate obtained in this embodiment is used for the detection of carbendazim ethanol solution, and the operation steps are the same as in Example 1. The experimental results of this embodiment are as follows: Figure 4 The image shows the SERS spectra of different concentrations of carbendazim in this embodiment, and the SERS spectra at 1268 cm⁻¹. -1 The graph shows the relationship between the SERS intensity of different concentrations of carbendazim and the concentration.

[0061] Example 5:

[0062] In this embodiment, the preparation of the SERS substrate is the same as in Example 1. A pesticide standard of a certain concentration gradient is added dropwise to the surface of fruits and vegetables; after the solvent has completely evaporated, a cotton swab is dipped in a small amount of solvent and used to wipe the surface of the fruits and vegetables; the cotton swab used to wipe the pesticide residue is placed in a centrifuge tube containing a small amount of solvent for sample preparation; the sample with pesticide residue is placed in an ultrasonic machine for ultrasonication; the ultrasonicated sample is then subjected to SERS detection using a Raman spectrometer.

[0063] like Figure 5 The SERS spectrum of thiram pesticide residues detected on the surface of fruits and vegetables shows a detection limit as low as 0.33 ng / cm³. 2 .

[0064] Example 6:

[0065] In this embodiment, the preparation of the SERS substrate is consistent with that in Example 1. The obtained SERS substrate is used for the detection of paraquat residues on fruit peels, and the operation steps are the same as in Example 5. Figure 6 The SERS spectrum of paraquat pesticide residues detected on the surface of fruits and vegetables shows a detection limit as low as 0.26 pg / cm³. 2 .

[0066] Example 7:

[0067] The preparation of the SERS substrate in this embodiment is consistent with that in Example 1. The SERS substrate obtained in this embodiment is used for the detection of carbendazim pesticide residues on fruit peels, and the operation steps are the same as in Example 5. Figure 7 The SERS spectrum of carbendazim pesticide residues detected on the surface of fruits and vegetables shows a detection limit as low as 4.29 ng / cm³. 2 .

[0068] In the SERS detection of Examples 1 to 7 above, the specific parameters such as reagents and reaction conditions can be adjusted as needed, and they are not directly related to the improvement points of this invention, so they are not described in detail.

[0069] Figure 8 The SERS substrate prepared in Example 1 of this invention was used to detect a concentration of 10. -14 SERS spectrum of M-ATP.

[0070] The technical solution of the present invention has been described above with reference to the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvements made using the inventive concept and technical solution of the present invention, or the direct application of the inventive concept and technical solution to other situations without modification, are all within the protection scope of the present invention.

[0071] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A simplified method for preparing Au-Ag Janus nanomaterials, characterized in that, Includes the following steps: (1) Gold nanoparticle (AuNPs) solution was prepared by hydrothermal reduction method; (2) Using the gold nanoparticle solution obtained in step (1) as a precursor, AgNO3 is reduced with β-cyclodextrin under alkaline conditions to form Au-Ag Janus; The preparation method of gold nanoparticles in step (1) includes the following steps: A. Prepare an aqueous solution of chloroauric acid, store it at 4°C protected from light, and use it for later use; B. Place ultrapure water in a reactor, add a magnetic wave, place it in an oil bath, and heat and stir until boiling. C. Add the aged chloroauric acid aqueous solution to water, add the reducing agent solution, and continue heating and stirring until the solution changes from colorless to wine red. D. Stop heating and continue stirring while cooling; E. Store in the refrigerator for later use; The reducing agent in step C is sodium citrate; The preparation method of Au-Ag Janus in step (2) includes the following steps: a. Place the prepared gold nanoparticle solution into a centrifuge and centrifuge; b. Discard the supernatant, add ultrapure water to re-dissolve the nanoparticles, and place them in an ultrasonic machine to disperse the nanoparticles evenly; c. Add the reducing agent β-cyclodextrin (β-CD) powder and gold nanoparticle solution to ultrapure water, and place them in an oil bath for stirring and heating; d. Add alkaline solution to adjust the pH of the reaction system while stirring; e. Add AgNO3 solution to the reaction system and continue heating and stirring; f. Allow the nanoparticles to cool naturally to room temperature, then centrifuge and wash them for later use.

2. The simplified method for preparing Au-Ag Janus nanomaterials according to claim 1, characterized in that, In step d, the alkaline solution is an aqueous solution of NaOH.

3. The simplified method for preparing Au-Ag Janus nanomaterials according to claim 1, characterized in that, In step c, the temperature is heated to 95-98°C.

4. The simplified method for preparing Au-Ag Janus nanomaterials according to claim 1, characterized in that, The stirring time in step e is 30-40 minutes.

5. A simplified Au-Ag Janus nanomaterial, prepared by any one of the methods described in claims 1-4.

6. The application of the simplified Au-Ag Janus nanomaterial as described in claim 5 in pesticide residue detection.

7. The application according to claim 6, characterized in that, The pesticide is one or more of thiram, paraquat, and carbendazim.

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