Preparation method and application of patterned silver-coated gold Au@Ag nanostructure substrate

Abstract

The application belongs to the technical field of Raman substrates, and particularly relates to a preparation method and application of a patterned silver-coated gold Au@Ag nanostructure substrate. The patterned silver-coated gold Au@Ag nanostructure substrate in-situ synthesizes an Ag shell layer by taking patterned Au nanostructures with uniform particle sizes and close packing as a template, the Ag uniformly wraps each Au nanoparticle, and a high-quality patterned silver-coated gold Au@Ag core-shell nanostructure is obtained, without introducing any additional stabilizer and without a complex experimental step flow, and the stable and universal preparation of the SERS substrate with high sensitivity and high enhancement uniformity provides a reference. Due to the synergistic effect of Au and Ag, the SERS effect of the substrate is enhanced, the Raman enhancement effect of the nanostructure is stronger than that of the patterned Au nanostructure, which is more conducive to the detection and analysis of molecules, and the problem of easy oxidation of the Ag shell is avoided, and the nanostructure has good signal enhancement uniformity.

Description

Technical Field

[0001] This invention belongs to the technical field of Raman substrates, specifically relating to a method for preparing and applying a patterned silver-coated gold Au@Ag nanostructure substrate. Background Technology

[0002] Surface-enhanced Raman scattering (SERS) is a highly sensitive, non-destructive characterization technique widely used in trace detection, bioimaging, and compound analysis. With the continuous development of nanomaterial preparation technology and the improvement of signal detection systems, SERS detection technology has made rapid progress, playing an indispensable role in many fields and possessing promising prospects and broad application potential. However, SERS detection technology still faces some challenges, such as the stability of the structure and properties of the SERS substrate. In the testing environment, if the substrate structure and chemical properties are unstable, such as particle aggregation in nanoparticle substrates or oxidation of the metal surface in metal nanostructure substrates, the Raman enhancement effect of the substrate will be greatly weakened, until it completely loses its Raman enhancement capability.

[0003] Ag nanoparticles are nanomaterials with surface plasmon resonances (SPRs). Under excitation light ranging from 300 nm to 1200 nm, Ag nanoparticles exhibit a strong Raman effect. However, Ag nanoparticles are highly unstable and their surfaces are easily oxidized, significantly reducing the Raman enhancement effect. Under excitation light of 632.8 nm, Au exhibits excellent Raman enhancement, while at 514.2 nm, it shows only a weak effect. In contrast, Ag exhibits strong Raman enhancement under different excitation light conditions. Studies have shown that because Au and Ag have different plasmon resonance peaks, the plasmon resonance peaks of gold-silver bimetallic materials change with variations in the gold and silver composition.

[0004] In recent years, numerous methods have been explored for preparing bimetallic nanoparticles, including deposition-precipitation, seed-mediated methods, co-precipitation, displacement methods, and template growth methods. The synergistic effect between different types of noble metal nanoparticles makes these bimetallic nanoparticles with Raman enhancement suitable for detecting various illicit food additives, explosives, DNA strands, proteins, and environmental pollutants. However, the introduction of surfactants has a certain impact on trace detection. Added surfactants may become impurities or adsorb onto the nanoparticle surface, affecting the sensitivity and signal reproducibility of Raman analysis. Furthermore, these preparation methods struggle to produce Raman substrates with uniformly distributed "hot spots," resulting in poor Raman signal uniformity, which is unsuitable for practical analysis. Therefore, developing a simpler method for synthesizing bimetallic SERS substrates that can produce synergistic effects and enhance Raman performance is crucial. Summary of the Invention

[0005] To address the above problems, the present invention aims to provide a method for preparing and applying a patterned silver-coated gold Au@Ag nanostructure substrate.

[0006] The technical content of this invention is as follows:

[0007] This invention provides a method for preparing a patterned silver-coated gold Au@Ag nanostructure substrate, comprising the following steps:

[0008] 1) Fabrication of silicon wafers with patterned Au nanostructures;

[0009] The Au nanostructure is shown below:

[0010] Its lower end grows on a silicon wafer, where m and n are natural numbers;

[0011] 2) Fabrication of patterned silver-coated gold Au@Ag nanostructure substrates

[0012] In an inert gas atmosphere, the silicon wafer with patterned Au nanostructures described in step 1) is added to a substrate containing Ag. + The silicon wafer is immersed in a mixed solution, then reacted at 80°C. After the reaction is resolved, the wafer is removed, ultrasonically treated, cleaned to remove metal deposits, and dried to obtain a patterned silver-coated gold Au@Ag nanostructure substrate.

[0013] The one containing Ag + The mixed solution is a mixture of silver salt and organic solution;

[0014] The solid-liquid ratio of the silver salt to the organic solution is 1:(100-120)mg / mL;

[0015] The organic solution includes one or more of ethanol and DMF.

[0016] The one containing Ag + In the mixed solution, the mixing ratio can be selected according to the thickness of the silver layer; under different ratios, the more DMF, the thicker the silver layer.

[0017] Step 1) describes the fabrication of the silicon wafer with the patterned Au nanostructure as follows:

[0018] 1.1) Grafting initiator on silicon wafer surface

[0019] The silicon wafer was treated and cleaned with piranha solution (H2O2:H2SO4 = 3:7), then immersed in a mixed solution of toluene, triethylamine and BPASiCl, and left to stand overnight. The silicon wafer surface after being immersed in piranha solution has a large number of oxygen-containing groups such as hydroxyl groups, which can undergo esterification reaction (grafting) with BPASICL in an alkaline environment. After the reaction is completed, the surface-modified silicon wafer is thoroughly rinsed with toluene and ethanol, and then vacuum dried to obtain the silicon wafer with surface grafting initiator BPASiCl.

[0020] The BPASiCl is prepared as follows:

[0021]

[0022] α-Bromophenylacetic acid was thoroughly mixed with 5-hexenyl-1-ol and DMAP, pre-cooled at 0°C, and then slowly added dropwise in a solution of N,N'-dicyclohexylcarbodiimide (DCC) dissolved in DCM. After the addition was complete, the mixture was stirred and allowed to naturally warm to room temperature, where it was stirred again. After the reaction was complete, the mixture was filtered, and the filtrate was collected. The solvent was removed by rotary evaporation, and the solution was then purified by silica gel column chromatography to obtain α-bromophenylacetic acid hexenyl ester.

[0023] α-Bromophenylhexenyl acetate and dichlorodimethylsilane were mixed and pre-cooled at 0°C. Nitrogen gas was then introduced and bubbled. KARSTTEDT catalyst was added, and the mixture was stirred and allowed to naturally warm to room temperature. The mixture was then stirred at room temperature. After the reaction was complete, the solvent was removed by rotary evaporation, and the solution was filtered once using a 0.22 μm PTFE filter. The resulting filtrate was BPASiCl.

[0024]

[0025] 1.2) Preparation of patterned PDMAEMA polymer brushes

[0026] Under an argon atmosphere, with the surface-grafted BPASiCl silicon wafer facing upwards, a mixed solution containing PTH, DMF, and DMAEMA purified by silica gel column chromatography is slowly applied to the silicon wafer surface, ensuring complete coverage. Then, a mask with the desired pattern is placed on top of the droplet, forming a thin liquid layer between the mask and the silicon wafer surface. The silicon wafer is then irradiated under a 365nm ultraviolet light source. The substrate is then removed from the glove box and thoroughly washed with DCM reflux in a Soxhlet extractor to remove unpolymerized monomers. Vacuum drying yields a silicon wafer with a patterned PDMAEMA polymer brush. The PDMAEMA structure on the silicon wafer is shown below.

[0027]

[0028] The PTH used was prepared as follows:

[0029]

[0030] Phenothiazine, chlorobenzene, NaOtBu, RuPhos, RuPhos-G2, and 4 mL of dioxane were mixed under an argon atmosphere and heated to react, turning the solution black. After the reaction was complete, the mixture was dissolved in DCM, transferred to a separatory funnel, washed three times with water, and separated. The product was in the organic phase. The organic phase was dried with anhydrous sodium sulfate, then filtered and the filtrate was collected. The solvent was removed by rotary evaporation, and the product was then purified by silica gel column chromatography to obtain white crystalline PTH.

[0031] 1.3) Preparation of patterned PDMAEMA-b-PMMA block copolymer polymer brushes

[0032] Under an argon atmosphere, a silicon wafer with a patterned PDMAEMA polymer brush was placed face up. A drop of a mixed solution containing PTH, DMF, and purified MMA was dropped onto the silicon wafer surface, ensuring the droplet completely covered the surface. A coverslip was then placed on top of the droplet, forming a thin liquid layer between it and the silicon wafer. The entire apparatus was irradiated with a 365nm ultraviolet light source. The silicon wafer was then placed in a Soxhlet extractor for DCM reflux cleaning and vacuum drying, resulting in a silicon wafer with a patterned PDMAEMA-b-PMMA block copolymer polymer brush grown on its surface. The structure of the PDMAEMA-b-PMMA block copolymer on the silicon wafer is shown below:

[0033]

[0034] 1.4) Preparation of patterned PMETAC-b-PMMA block copolymer polymer brushes

[0035] Under an argon atmosphere, acetone, iodomethane, and a silicon wafer with a patterned PDMAEMA-b-PMMA block copolymer polymer brush grown on its surface are mixed and reacted at room temperature. After the reaction is complete, the filtrate is discarded, and the iodomethane residue is thoroughly washed with acetone, followed by vacuum drying. The amino groups on the PDMAEMA blocks are converted into positively charged NH4 under the action of potassium iodide. + A silicon wafer with a patterned PMETAC-b-PMMA block copolymer polymer brush was obtained. The structure of the PMETAC-b-PMMA block copolymer on the silicon wafer is shown below:

[0036]

[0037] 1.5) Preparation of patterned Au nanostructures

[0038] A silicon wafer with a patterned PMETAC-b-PMMA block copolymer polymer brush was immersed in a mixed solution containing HAuCl4·3H2O, TBAB, oleylamine, and DMF under an argon atmosphere to ensure that as much chloroaurate ion precursor as possible was loaded into the patterned PMETAC block regions. The reaction was carried out at 90°C for 24 hours. After the reaction, the silicon wafer was added to ethanol and ultrasonically treated to remove Au nanoparticles generated outside the PMETAC block pattern on the silicon wafer surface. Vacuum drying was then performed to obtain a silicon wafer with a patterned Au nanostructure. The patterned Au nanostructure on the silicon wafer is shown below:

[0039] In the above structure, m and n are both natural numbers.

[0040] The present invention also provides a patterned silver-coated gold Au@Ag nanostructure substrate obtained by the above preparation method, which has nanoparticles with Ag as the shell and Au as the core, forming a patterned core-shell nanostructure with uniform particle size and dense packing.

[0041] This invention also provides the application of patterned silver-plated gold Au@Ag nanostructure substrates in the fabrication of SERS sensors.

[0042] This invention also provides an application of patterned silver-coated gold Au@Ag nanostructure substrate in the quantitative and qualitative detection of pesticide residues;

[0043] The pesticide residues mentioned include thiram.

[0044] This invention also provides an application of patterned silver-coated gold Au@Ag nanostructure substrate in the detection of chemical dyes;

[0045] The chemical dyes include 4-AMTP, 4-MBA, and methylene blue.

[0046] The beneficial effects of this invention are as follows:

[0047] The method for preparing patterned silver-coated gold Au@Ag nanostructure substrate of the present invention uses patterned Au nanostructures with uniform particle size and dense packing as templates to synthesize Ag shells in situ. Ag uniformly coats each Au nanoparticle, resulting in high-quality patterned silver-coated gold Au@Ag core-shell nanostructures. This method does not require the introduction of any additional stabilizers or complex experimental procedures. It can provide a reference for the stable and universal preparation of SERS substrates with high sensitivity and high enhancement uniformity.

[0048] The patterned silver-coated gold Au@Ag nanostructure substrate of the present invention enhances the SERS effect of the substrate due to the synergistic effect of Au and Ag. The Raman enhancement effect of this nanostructure is stronger than that of patterned Au nanostructures, which is more conducive to molecular detection and analysis. It also avoids the problem of easy oxidation of Ag shell and has good signal enhancement uniformity.

[0049] The application of the patterned silver-coated gold Au@Ag nanostructure substrate of this invention, due to the strong SERS effect of this nanostructure base, can be used for the detection of Raman signal intensity. Specifically, the detection limit for 4-MBA molecules can reach 10. -10 M, EF height reaches 8.8×10 9 The relative standard deviation of the Raman signal intensity measured at ten random points was 6.72%. This substrate also possesses practical application performance, achieving a minimum detection concentration of 10 for the pesticide thiram. -8 M, and there is a linear relationship between the logarithm of the concentration of thiamethoxam and the corresponding Raman signal intensity, which can be used for quantitative detection. Attached Figure Description

[0050] Figure 1 This is a schematic diagram illustrating the fabrication of the patterned Au@Ag nanostructure SERS substrate of this invention;

[0051] Figure 2 This is a schematic diagram of the in-situ synthesis of patterned Au nanostructures;

[0052] Figure 3 This is a microscopic image of the array morphology of the patterned Au@Ag nanostructures of this invention;

[0053] Figure 4 SEM images of the microstructures of patterned Ag nanostructures, Au nanostructures, and Au@Ag nanostructures;

[0054] Figure 5 TEM images of the triangular Au@Ag nanostructures at low and high magnification;

[0055] Figure 6 This is a microscopic image of the core-shell structure of the patterned Au@Ag nanostructure of this invention;

[0056] Figure 7 AFM images of the triangular Au nanostructure and the Au@Ag nanostructure after removing the outer PMMA layer;

[0057] Figure 8 GI-WAXS curves for patterned Au@Ag nanostructures;

[0058] Figure 9 SEM images and particle size distribution histograms of Au@Ag nanoparticles;

[0059] Figure 10 TEM images of Au@Ag nanoparticles at different reaction times and the corresponding Ag shell thicknesses;

[0060] Figure 11 The image shows the Raman signal enhancement results of 4-MBA molecules by Au@Ag nanoparticles with different shell thicknesses.

[0061] Figure 12 The image shows the Raman signal enhancement results of 4-MBA molecules on patterned Ag nanostructure substrates, Au nanostructure substrates, and Au@Ag nanostructure substrates.

[0062] Figure 13 Raman signal results for different concentrations of 4-MBA molecules;

[0063] Figure 14 The graph shows the logarithmic relationship between the concentration of 4-MBA solution and the Raman signal intensity, as well as the results of linear fitting.

[0064] Figure 15 Raman signal intensities and histograms at ten random points on the surface of a patterned Au@Ag nanostructure substrate;

[0065] Figure 16 The electric field distribution of Au@Ag nanoparticles as simulated by FDTD;

[0066] Figure 17 The figure shows the Raman signals of different concentrations of thiram bimolecule and the relationship between the logarithm of thiram bimolecule concentration and its Raman signal intensity. Detailed Implementation

[0067] The present invention will be further described in detail below through specific implementation examples and accompanying drawings. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art fall within the scope of the appended claims.

[0068] Unless otherwise specified, all raw materials and reagents used in this invention are from the conventional market.

[0069] Example 1

[0070] A method for preparing a patterned silver-coated gold (Au@Ag) nanostructure SERS substrate, the process flow of which is as follows: Figure 1 As shown:

[0071] 1) Grafting initiator on silicon wafer surface

[0072] Silicon wafers were cut into 1.0cm × 0.5cm pieces and ultrasonically cleaned in EtOH. The wafers were then treated with a piranha solution (H₂O₂:H₂SO₄ = 3:7) at 120°C for 2 hours (Note: Care must be taken during the preparation and post-treatment of the piranha solution; improper operation may result in explosion or burns). After treatment, the wafers were thoroughly rinsed with plenty of deionized water and then dried in a vacuum oven at 40°C for 24 hours. Finally, the wafers were stored in an argon-filled glove box. The wafers were then immersed in a mixed solution of toluene (50mL), triethylamine (0.02mL), and BPASiCl (180μL) and allowed to stand overnight. After the reaction was complete, the surface-modified wafers were thoroughly rinsed with toluene and ethanol and then vacuum dried at 40°C to obtain the grafted initiator wafers.

[0073] The BPASiCl is prepared as follows:

[0074]

[0075] 10.0 g of 5-hexenyl-1-ol, 6.8 mL of α-bromophenylacetic acid, and 0.5 g of DMAP were added to a 250 mL round-bottom flask equipped with a magnetic stirrer. After thorough mixing, the reaction solution was pre-cooled at 0 °C. 10.7 g of N,N'-dicyclohexylcarbodiimide was dissolved in 40 mL of DCM and then slowly added dropwise to the round-bottom flask. After the addition was complete, the mixture was stirred and allowed to warm naturally to room temperature. The mixture was stirred at room temperature for 24 h. After the reaction was complete, the mixture was filtered, and the filtrate was collected. The solvent was removed by rotary evaporation, and the solution was then purified by silica gel column chromatography (eluent: PE:EA = 30:1) to obtain a colorless and transparent liquid (α-bromophenylacetic acid hexenyl ester) (12.23 g, 87.8%).

[0076] 2) Preparation of patterned PDMAEMA polymer brushes

[0077] Under an argon atmosphere, a silicon wafer grafted with BPASiCl was placed face up in a culture dish. A mixed solution containing PTH (32 mg, 0.1169 mmol, relative monomer concentration 5.0 mol%), DMF (100 μL), and purified DMAEMA (400 μL, 2.37 mmol) was dropped onto the silicon wafer surface, ensuring complete coverage. A mask with the desired pattern was then placed on top of the droplet, forming a thin liquid layer between the mask and the silicon wafer surface. The culture dish was placed approximately 10 cm below a 365 nm UV light source at approximately 80 μW / cm². 2The culture dish was irradiated with ultraviolet light of high intensity for 30 min. Then, the substrate was removed from the glove box and washed with DCM reflux in a Soxhlet extractor for 12 h to thoroughly remove unpolymerized monomers. Finally, it was vacuum dried at 40 °C to obtain a silicon wafer with patterned PDMAEMA polymer brush.

[0078] The PTH used was prepared as follows:

[0079]

[0080] Under an argon atmosphere, 0.739 g of phenothiazine, 0.531 mL of chlorobenzene, 0.498 g of NaOtBu, 0.030 g of RuPhos, 0.052 g of RuPhos-G2, and 4 mL of dioxane were added to a 25 mL round-bottom flask equipped with a magnetic stirrer. The reaction solution was heated at 110 °C for 5 h, and the solution turned black. After the reaction was complete, the product was dissolved in DCM, transferred to a separatory funnel, washed three times with water, and separated. The product was in the organic phase. The organic phase was dried with anhydrous sodium sulfate, then filtered and the filtrate was collected. The solvent was removed by rotary evaporation, and then purified by silica gel column chromatography (eluent: PE:DCM = 97:1) to obtain white crystals (PTH) (1.2 g, 94%).

[0081] 3) Preparation of patterned PDMAEMA-b-PMMA block copolymer polymer brushes

[0082] Under an argon atmosphere, a silicon wafer with a patterned PDMAEMA polymer brush was placed face up in a petri dish. A drop of a mixed solution containing PTH (5.2 mg, 0.019 mmol, relative monomer concentration 0.5 mol%), DMF (100 μL), and purified MMA (400 μL, 3.74 mmol) was dropped onto the silicon wafer surface, ensuring complete coverage. A coverslip was then placed on top of the droplet, forming a thin liquid layer between it and the silicon wafer. The entire apparatus was placed approximately 4 cm below a 365 nm ultraviolet light source with an intensity of approximately 80 μW / cm². 2 The device was irradiated with ultraviolet light for 15 minutes. The culture dish was removed from the glove box, and the silicon wafer was placed in a Soxhlet extractor and washed with DCM reflux for 12 hours. It was then vacuum dried at 40°C to obtain a silicon wafer with patterned PDMAEMA-b-PMMA block copolymer polymer brushes grown on its surface.

[0083] 4) Preparation of patterned PMETAC-b-PMMA block copolymer polymer brushes

[0084] Acetone (18 mL), methyl iodide (2 mL), and a silicon wafer with patterned PDMAEMA-b-PMMA block copolymer polymer brushes grown on its surface were added to a 100 mL Erlenmeyer flask with a ground glass stopper under an argon atmosphere. The flask was sealed with a glass stopper, and the reaction was carried out at room temperature for 12 h. After the reaction was completed, the filtrate was discarded, and the methyl iodide residue was thoroughly washed with acetone. Then, the wafer was dried under vacuum at 40 °C to obtain the silicon wafer with the patterned PDMAEMA-b-PMMA block copolymer polymer brushes.

[0085] 5) Preparation of patterned Au nanostructures

[0086] Under an argon atmosphere, a silicon wafer with a patterned PMETAC-b-PMMA block copolymer polymer brush was placed in a 25 mL Schlenk flask. A freshly prepared mixed solution containing HAuCl4·3H2O (2.5 mg, 0.06 mmol), TBAB (0.1 mg, 0.0003 mmol), oleylamine (15 μL, 0.05 mmol), and 1 mL DMF was added. The silicon wafer was immersed in this solution for 7 days to ensure that the chloroaurate ion precursor was loaded as much as possible within the patterned PMETAC block regions. The silicon wafer was then reacted in the mixed solution at 90 °C for 24 h. After the reaction, the silicon wafer was removed from the Schlenk flask and placed in another clean glass bottle. 2 mL of EtOH was added to the glass bottle, and the mixture was sonicated for 15 min using a 180 W ultrasonicator to remove Au nanoparticles generated outside the PMETAC block pattern area on the silicon wafer surface. The wafer was then vacuum dried at 40 °C to obtain a silicon wafer with a patterned Au nanostructure.

[0087] The reaction flow of steps 1) to 5) above is as follows: Figure 2 As shown.

[0088] 6) Preparation of patterned silver-coated gold (Au@Ag) nanostructure substrates

[0089] A silicon wafer with patterned Au nanostructures was placed in a 25 mL Schlenk flask under an argon atmosphere, and a mixed solution containing AgNO3 (6 mg, 0.35 mmol), EtOH (5 μL), and 0.5 mL DMF was added. The wafer was soaked for one day, followed by reaction at 80 °C for 24 h. After the reaction, the silicon wafer was transferred from the Schlenk flask to another clean glass bottle, and 3 mL of EtOH was added. The bottle was then sonicated for 20 min using a 180 W sonicator, followed by the addition of 3 mL of DMF. Sonication for another 20 min was performed to remove metal deposits outside the patterned area on the silicon wafer surface. The wafer was then vacuum dried at 40 °C to obtain a patterned silver-coated gold Au@Ag nanostructure substrate.

[0090] Example 2

[0091] Preparation of patterned Ag nanostructures

[0092] 1) Fabrication of patterned PtBA polymer brushes based on silicon wafers

[0093] Under an argon atmosphere, a silicon wafer with the surface grafting initiator (step 1) from Example 1) was placed face up in a petri dish. Using a 100 μL pipette, a mixed solution of PTH (5.2 mg, 0.019 mmol, relative monomer concentration 0.5 mol%), DMF (100 μL), and purified tBA (540 μL, 3.74 mmol) was dropped onto the silicon wafer surface to completely cover it. Then, a mask with the desired pattern was placed over the silicon wafer surface, forming a thin liquid layer between the mask and the wafer. Subsequently, the entire system was placed at a wavelength of 365 nm and an intensity of approximately 80 μW / cm². 2 About 4cm below the UV lamp ( Figure 2-4 The silicon wafers were then exposed to ultraviolet light for 5, 10, 15, 20, or 25 minutes. The system was then removed from the glove box and refluxed with DCM in a Soxhlet extractor for 12 hours to thoroughly clean away any unpolymerized monomers from the silicon wafer surface. Finally, the wafers were vacuum dried at 40°C.

[0094] 2) Preparation of patterned PtBA-b-PMMA block copolymer polymer brushes based on silicon wafers

[0095] Under an argon atmosphere, a silicon wafer with a patterned PtBA polymer brush was placed face up in a petri dish. A mixture of PTH (5.2 mg, 0.019 mmol, relative monomer concentration 0.5 mol%), DMF (100 μL), and purified MMA (400 μL, 3.74 mmol) was pipetted into the silicon wafer surface using a 100 μL pipette. The mixture was then dropped onto the silicon wafer surface, ensuring complete coverage. A transparent coverslip was then placed on the silicon wafer surface, creating a thin liquid layer between the coverslip and the wafer surface. The entire system was then placed at a wavelength of 365 nm and an intensity of approximately 80 μW / cm². 2 The wafer was placed approximately 4 cm below a UV lamp and irradiated for 15 minutes. Afterward, the wafer and coverslip were removed from the glove box and placed in a Soxhlet extractor. The wafer was thoroughly cleaned with DCM and refluxed for 12 hours, then vacuum dried at 40°C.

[0096] 3) Preparation of patterned PAA-b-PMMA block copolymer polymer brushes based on silicon wafers

[0097] Add 5 mL of DCM, 10 mL of TFA, and a silicon wafer with a patterned PtBA-bPMMA block copolymer polymer brush to a 250 mL Erlenmeyer flask and react at room temperature for 24 h. Rinse the silicon wafer three times with DCM to thoroughly remove reaction residues, and then vacuum dry at 40 °C.

[0098] 4) Fabrication of patterned Ag nanostructures based on silicon wafers

[0099] Under an argon atmosphere, a silicon wafer coated with a patterned PAA-b-PMMA block copolymer polymer brush was placed in a 25 mL Schlenk flask, and then a freshly prepared mixed solution containing AgNO3 (12 mg, 0.07 mmol), 1 mL DMF, and the reducing agent EtOH (10 μL) was added. The silicon wafer was immersed in this solution for 2 days to ensure that the patterned PAA block regions were loaded with Ag as much as possible. + Precursor. Then, the Schlenk flask was removed from the glove box and reacted at 80°C for 24 h. After the reaction was complete, the silicon wafer was removed from the Schlenk flask and placed in another clean glass bottle. 2 mL of DMF was added, and the bottle was sonicated for 15 min in a 180 W sonicator to remove Ag nanoparticles formed on the silicon wafer surface outside the PAA block pattern. Then, it was thoroughly cleaned with EtOH and vacuum dried at 40°C.

[0100] 1. The morphology and composition of the patterned Au@Ag nanostructures prepared in Example 1 were analyzed.

[0101] The array morphology of the Au@Ag nanostructures was characterized using SEM, such as... Figure 3 As shown, the triangular nanostructure array perfectly replicates the patterned Au nanostructure pattern. The equilateral triangles have sides of 20 μm each, with clearly discernible edges. EDS elemental analysis confirmed the composition of the patterned nanostructures, such as... Figure 3 As shown in c and d, the simultaneous appearance of triangular arrays of Au and Ag elements proves that the patterned Au@Ag nanostructure prepared in this invention is composed of Au and Ag elements.

[0102] The microstructures of the patterned Ag, Au, and Au@Ag metal nanostructures prepared above were characterized using SEM, such as... Figure 4 As shown. Figure 4 a, b and Figure 4The microstructures of patterned Ag nanostructures, Au nanostructures, and Au@Ag nanostructures prepared using the same copolymer brush template are shown. It can be observed that the nanoparticles with uniform particle size are tightly packed together, which proves the versatility and good controllability of the template method for preparing two-dimensional inorganic nanostructures, and provides a basis for the preparation of SERS substrates with good reinforcement effect.

[0103] The microstructure of the patterned Au@Ag nanostructure was characterized using TEM. Figure 5 As shown, the triangular Au@Ag nanostructures can be easily peeled off the silicon wafer surface while maintaining structural integrity. This is attributed to the tight bonding between the PMETAC blocks and the nanoparticles, which act as adhesives to the nanoparticles when peeled off along with the Au@Ag nanostructures, thus maintaining structural integrity. Wrinkling or folding of the triangular edges in some areas is due to the natural slight folding of the triangular film edges after peeling from the silicon wafer. High-magnification TEM images reveal a uniform and densely packed core-shell nanoparticle cluster with diameters ranging from 10 nm to 50 nm. This aggregated structure contains numerous "hot spots," laying the foundation for the fabrication of substrates with excellent Raman enhancement effects.

[0104] Under high magnification using scanning transmission electron microscopy (STEM), the core-shell structure of nanoparticles can be seen more clearly. For example... Figure 6 As shown, Au@Ag nanoparticles exhibit a bright center and dark outer ring morphology, indicating the formation of a core-shell structure with Au as the core and Ag as the shell. The absence of a core-shell morphology in some nanoparticles may be due to differences in the focal plane. To further verify the successful preparation of Au@Ag nanoparticles, EDS elemental analysis was used to characterize the elements contained in the nanoparticles and their distribution. The outer hollow ring pattern represents Ag, and the inner solid circle pattern represents Au. Ag completely and uniformly encapsulates Au in the shell, and the particle size distribution of Au in the core layer is relatively uniform. The thickness of Ag in the shell is also relatively consistent, indicating that the synthesis process of the Ag shell is stable and uniform, verifying the feasibility of the method for preparing patterned Au@Ag nanostructures using PMETAC-b-PMMA block copolymer polymer brushes.

[0105] The thickness and morphology of the patterned Au@Ag nanostructure were characterized using AFM. Figure 7As shown, after the outer PMMA blocks were burned off, the thickness of the triangular Au@Ag nanostructure was 45.4 ± 3.2 nm, which is higher than the thickness of the triangular Au nanostructure before the reaction. Furthermore, the surface of this triangular Au@Ag nanostructure is smooth, and the thickness is relatively uniform throughout, which also indicates that the synthesis process of the Ag shell was stable and controllable. This further demonstrates the successful preparation of a uniformly structured Au@Ag nanostructure, laying an important foundation for the preparation of SERS substrates with good signal enhancement stability.

[0106] The composition and structure of the prepared patterned Au@Ag nanostructures were characterized using GI-WAXD. Figure 8 The figures show the characteristic diffraction peaks of the crystal structure of patterned Au nanostructure, Ag nanostructure, and Au@Ag nanostructure, respectively, which further proves the formation of polycrystalline Au@Ag nanoparticles and verifies the feasibility of preparing Au@Ag nanostructures using a PDMAEMA-b-PMMA block copolymer polymer brush as a template.

[0107] According to TEM results, the average particle size of Au nuclei is 17.5 nm. Figure 9 To investigate the Ag shell thickness in Au@Ag nanoparticles at different reaction times, the reaction times for the Ag shell were set to 1.5 h, 3 h, 4.5 h, and 6 h, respectively. The morphology of the Au@Ag nanoparticles at different reaction times was characterized using TEM, and the Ag shell thickness at the corresponding reaction times was statistically analyzed. The results are as follows: Figure 10 As shown, as the reaction time increased from 1.5 h to 4.5 h, Ag uniformly encapsulated the Au core as a shell, with the thickness increasing slowly with increasing reaction time (2.4 nm, 4.0 nm, and 5.4 nm). The Au@Ag nanoparticles remained uniformly and tightly packed, forming many SERS "hot spots". When the reaction time continued to increase from 4.5 h to 6 h, the Ag shell became irregular, and the thickness increased significantly (11.2 nm). The irregular geometric shape became prominent, and the distribution of Au@Ag nanoparticles showed aggregation, with the number of "hot spots" greatly reduced.

[0108] To investigate the effect of Ag layer thickness on the SERS effect of patterned Au@Ag nanostructures, four patterned Au@Ag nanostructure substrates with different Ag layer thicknesses were used to detect the SERS effect at a 4-MBA concentration of 10⁻⁶. -6 Raman signal at time M. For example... Figure 11 As shown, 1078cm is still selected. -1Using the Raman signal peak intensity generated at the reference point, when the Ag layer thickness is less than 5.4 nm, as the Ag shell thickness increases, the Au@Ag nanoparticle size gradually increases, the particles pack more tightly, generating more "hot spots," and the Raman enhancement effect is enhanced. When the Ag shell thickness is further increased to 11.2 nm, due to the non-uniform particle size and particle aggregation, the SERS "hot spots" are greatly reduced, leading to a weakening of the SERS effect on the corresponding substrate. Therefore, a patterned nanostructure with an Ag layer thickness of 5.3 nm was selected as the optimal group, and subsequent experiments were conducted using a patterned nanostructure with an Ag layer thickness of 5.3 nm.

[0109] To compare the SERS effect strength of patterned Au@Ag nanostructures, Au nanostructures, and Ag nanostructures, 4-MBA was used as a probe molecule to investigate the properties of three different SERS substrates. Figure 12 As shown, three different substrates at a 4-MBA molecular concentration of 10 -6 In the case of M, the Raman signal enhancement effect varies greatly. (Using 1078 cm⁻¹) -1 Using the Raman signal peak intensity generated at the point of origin as a reference, the SERS effect of the patterned Au@Ag nanostructure is the strongest, followed by the SERS effect of the Ag nanostructure, and the SERS effect of the Au nanostructure is the weakest. It is speculated that this is due to some special electron transfer interaction between the Ag shell and the Au core, which increases the electron density of the Ag shell, thus causing the Ag shell to become a negative oxidation state of Ag. δ- Furthermore, the coupling between plasmons between the shell and the core enhances the SERS effect of the core-shell nanoparticles.

[0110] The Raman signal intensity of 4-MBA molecules at different concentrations was measured to evaluate the SERS sensitivity of Au@Ag nanostructures. Figure 13 As shown, the concentration of 4-MBA molecules ranges from 1 μm to 100 pm, and a 1078 cm⁻¹ concentration was selected. -1 Using the peak signal intensity as a reference, the Raman signal was very strong when the concentration of 4-MBA molecules was 1 μm. As the concentration of probe molecules gradually decreased from 1 μm to 100 pm, the intensity of the Raman signal generated on the substrate surface also decreased accordingly. Even when the concentration of 4-MBA molecules decreased to 100 pm, the enhancement effect of the substrate on the Raman signal of 4-MBA molecules could still be detected, indicating that the Au@Ag nanostructure substrate has relatively high sensitivity.

[0111] To further explore the feasibility of using this substrate for quantitative SERS detection, the Raman signal intensity of 4-MBA molecules at concentrations ranging from 1 μm to 1 pm was fitted. The results also revealed an adsorption-saturation Langmuir relationship between the 4-MBA molecule concentration and its Raman signal intensity: at very low concentrations, the substrate adsorption efficiency is strong, and increasing the 4-MBA probe molecule concentration significantly enhances the Raman signal intensity; however, as the concentration increases to a certain level, the substrate adsorption efficiency decreases until adsorption saturation occurs, and further increasing the probe molecule concentration slows down the enhancement trend of the Raman signal intensity. Figure 14 Plotting the logarithms of both concentration and peak intensity yields a fitting result of an R² line. 2 The linear correlation equation for the line with a value of 0.937 is as follows:

[0112] Log I1078 = 7.98 + 0.55log C 4-MBA

[0113] The feasibility of using Au@Ag nanostructured substrates for SERS quantitative analysis was verified.

[0114] To verify the reproducibility of the Raman enhancement effect in different regions of the patterned Au@Ag nanostructure, a 1.5 mm × 0.7 mm region was randomly selected on the substrate surface, and ten detection points were randomly selected within this region for SERS detection. Figure 15 As shown. By Figure 15 From b, we can see that the Raman signal intensity at each point is almost the same. Based on these ten Raman signals at 1078 cm⁻¹, -1 The signal strength at the location was calculated to have a relative standard deviation of approximately 6.72%, indicating that the "hot spots" are uniformly distributed in the substrate space, thus enabling the substrate to exhibit good Raman signal reproducibility and stability.

[0115] 2. SERSEF calculation of patterned Au@Ag nanostructures

[0116] To further demonstrate the SERS effectiveness of this patterned Au@Ag nanostructure, the average EF value of the substrate was calculated according to the following formula:

[0117] EF = [I SERS ] / [I bulk ]×[C bulk ] / [C SERS ]

[0118] I SERS and I bulk These are the Raman signals of 4-MBA and the Raman signal intensity of the sample itself, respectively; C SERS and C bulkThese represent the 4-MBA molecular concentrations on patterned Au@Ag nanostructure surfaces and bare silicon surfaces, respectively. 4-MBA was selected at a concentration of 1078 cm⁻¹. -1 The characteristic peak signal intensity at the location is calculated, and the I of 4-MBA is... SERS =790.3, C SERS =1×10 -10 M,I bulk =9.2, C bulk =1×10 - 2 The calculated value of M.EF is 8.59 × 10⁻⁶. 9 This further demonstrates the feasibility and superiority of the in-situ synthesis of Au@Ag nanostructures using a bottom-up technique.

[0119] 3. SERS simulation of patterned Au@Ag nanostructures

[0120] To further verify the SERS effect of the Au@Ag nanostructures, the electric field distribution on the surface of the Au@Ag nanostructures was simulated using a simple FDTD model. Based on experimental results, the parameters for the computational model were estimated. The diameter of the Au core nanoparticles was uniformly estimated at 17.5 nm, the Ag shell thicknesses were 2.4 nm, 4.0 nm, and 5.4 nm, and the spacing between nanoparticles was 2 nm. The SERS signal intensity was equal to E / E0, where E represents the strongest generated electric field intensity, E0 represents the incident electric field intensity, and EF is defined as |E / E0|. 4 In this linear simulation, a 785 nm plane wave source along the y-axis was used as the excitation source. The simulated electric field distributions of Au@Ag nanoparticles with different Ag shell thicknesses in the xz plane are shown below. Figure 16 As shown in the figure, the simulation results reveal a very strong electric field enhancement at the gaps between Au@Ag nanoparticles, known as "hot spots." This electric field enhancement at the hot spots increases with the thickness of the silver shell layer. The strongest electric field enhancement occurs at the hot spots of the Au@Ag nanostructure when the Ag shell thickness reaches 5.4 nm, with a maximum electric field enhancement (EF) of 10⁸. This strong EF can be attributed to the gaps created by the close packing of Au@Ag nanoparticles and the tight coupling between the core and shell elements. The simulation results are largely consistent with the experimental calculations, fully demonstrating the strong SERS effect of patterned Au@Ag nanostructures and providing a theoretical possibility for preparing Au@Ag nanostructures using copolymer brushes for SERS substrates.

[0121] 4. Patterned Au@Ag nanostructures for pesticide residue detection

[0122] To investigate the practical application performance of Au@Ag nanostructures as SERS substrates, the Raman signal enhancement effect of Au@Ag nanoparticles on the common pesticide thiram was studied. The results are as follows: Figure 17 As shown, the Raman signal of thiram gradually increases with the concentration of thiram from 10 nm to 10 μm. Using Raman spectra acquired by confocal laser, characteristic fingerprint information of target probe molecules such as thiram can be obtained simply and efficiently through an Au@Ag substrate. Even at an ultra-low concentration of thiram at 10 nm, the Raman signal at 1378 cm⁻¹... -1 The signal at the location of (the characteristic Raman signal of methimazole) can also be accurately detected. A 1378cm² measurement was selected. -1 Using the signal peak intensity at a given location as a reference, the relationship between the Raman signal intensity and concentration of the thiamethoxam bimolecule in the concentration range of 10 nm to 10 μm was plotted. The results conform to a linear equation:

[0123] Log I1078=54232+6603log C 4-MBA

[0124] Among them, R 2 =0.948, indicating that this substrate is promising for practical quantitative testing.

Claims

1. A method for preparing a patterned silver-coated gold Au@Ag nanostructure substrate, characterized in that, Includes the following steps: 1) Fabrication of silicon wafers with patterned Au nanostructures; The patterned Au nanostructure is shown below: Its lower end grows on a silicon wafer, where m and n are natural numbers; 2) Fabrication of patterned silver-coated gold Au@Ag nanostructure substrates In an inert gas atmosphere, the silicon wafer with patterned Au nanostructures described in step 1) is added to a substrate containing Ag. + The silicon wafer is immersed in a mixed solution, then reacted at 80°C. After the reaction is resolved, the wafer is removed, ultrasonically treated, cleaned to remove metal precipitates, and dried to obtain a patterned silver-coated gold Au@Ag nanostructure substrate.

2. The preparation method according to claim 1, characterized in that, The one containing Ag + The mixed solution is a mixture of silver salt and organic solution.

3. The preparation method according to claim 2, characterized in that, The solid-liquid ratio of the silver salt to the organic solution is 1:(100~120) mg / mL.

4. The preparation method according to claim 2, characterized in that, The organic solution includes one or more of ethanol and DMF.

5. A patterned silver-coated gold Au@Ag nanostructure substrate obtained by the preparation method according to any one of claims 1-4, characterized in that, It has nanoparticles with Ag as the shell and Au as the core, forming a patterned core-shell nanostructure with uniform particle size and dense packing.

6. The application of the patterned silver-plated gold Au@Ag nanostructure substrate as described in claim 5 in the fabrication of SERS sensors.

7. The application of the patterned silver-coated gold Au@Ag nanostructure substrate as described in claim 5 in the quantitative and qualitative detection of pesticide residues, characterized in that, The pesticide residues mentioned include thiram.

8. The application of the patterned silver-coated gold Au@Ag nanostructure substrate as described in claim 5 in the detection of chemical dyes; The chemical dyes include 4-AMTP, 4-MBA, and methylene blue.

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