Preparation method of Au@AgNPs-PDMS film SERS detection platform and application in detection of cosmetic asiaticoside

Abstract

The application discloses a kind of Au@AgNPs-PDMS film SERS detection platform preparation method and its application in cosmetic asiaticoside detection.The method is first prepared spherical, flower-like, hexagonal three kinds of AgNPs, with asiaticoside as target object, and the flower-like AgNPs with optimal enhancement effect are screened out;Subsequently, Au@Ag core-shell nanoparticles are prepared by seed growth method;Then, PDMS film is treated by plasma hydrophilization and modified by APTMS silanization;Finally, the uniform self-assembly of Au@AgNPs on the surface of PDMS film is realized through the chemical interaction between Ag and amino group.When the detection platform is applied to cosmetic asiaticoside detection, the sample is pretreated first, then SERS spectrum is collected, and finally OPLS-DA and LDA models are used for qualitative identification.The detection limit of the method is 25nM, the linear range is 0.01-0.5mg / mL, the detection time is within 10min, and the method has the advantages of high sensitivity, rapid detection, simple operation, low cost, etc., and is suitable for cosmetic production quality control and market supervision on-site rapid detection.

Description

Technical Field

[0001] This invention relates to the field of biodetection technology, specifically to an Au@AgNPs... Preparation method of PDMS thin film SERS detection platform and its application in the detection of asiaticoside in cosmetics. Background Technology

[0002] Surface-enhanced Raman scattering (SERS) technology has become an ideal technique for the rapid detection of active ingredients and prohibited additives in cosmetics due to its high sensitivity, fingerprint recognition specificity, and rapid detection advantages. The morphology, size, and surface structure of noble metal nanomaterials are core factors determining SERS performance, directly affecting the number of "hot spots" and the local electric field strength between nanoparticles. Polydimethylsiloxane (PDMS), as a hydrophobic and flexible polymer material, possesses advantages such as Raman signal inertness, good chemical stability, excellent film-forming properties, and enrichment of analytes in aqueous solutions, making it an ideal supporting substrate for solid-state SERS. Combining Au@Ag core-shell nanoparticles with PDMS films can immobilize liquid nanoparticles into a solid-state SERS detection platform, retaining the excellent SERS enhancement performance of the Au@Ag core-shell structure while solving the problems of poor stability and insufficient practicality of liquid sols.

[0003] Patent CN114660043B discloses a method for preparing a SERS substrate based on elastic contraction, the SERS substrate itself, and a detection method thereof. This patent utilizes elastic PDMS as a substrate. After saturated self-assembly of silver nanoparticles on the stretched PDMS surface, the tension is released, causing the substrate to contract and form a bidirectional wrinkled structure, thus shortening the spacing between the silver particles and creating an effective hot spot. The PDMS substrate of this patent can be directly attached to the surface of any shaped solid sample for rapid, in-situ detection. However, this technical solution has the following shortcomings: the patent only uses pure silver nanoparticles and does not employ an Au@Ag core-shell structure, thus limiting its optical performance and chemical stability; it does not involve the screening and optimization of multi-morphological AgNPs, making it impossible to perform targeted optimization of the SERS enhancement effect for specific detection targets (such as asiaticoside); and it does not establish a chemometric qualitative and quantitative model for the complex matrix of cosmetics, making it impossible to achieve accurate detection of asiaticoside in cosmetics.

[0004] Patent CN110346350B discloses a method for preparing a SERS substrate, a SERS structure within a microfluidic channel, and a microfluidic SERS detection method. This patent involves coating a substrate with photoresist, performing 3D laser printing, development, and supercritical drying to obtain a polymer microstructure, then setting a SERS functional layer on its surface, and finally adding liquid and using capillary evaporation to obtain a nano-interstitial structure. However, this technical solution has the following shortcomings: The patent does not use a PDMS film as a flexible support substrate, thus lacking the natural adsorption and enrichment characteristics of PDMS materials for weakly polar molecules; it does not involve the preparation of Au@Ag core-shell nanoparticles, making it impossible to utilize the tunable optical properties of the core-shell structure; and it does not establish a corresponding method system for the detection of asiaticoside in cosmetics, as the detection target and application field differ from this invention.

[0005] In summary, existing technologies lack a complete technical solution for the detection of asiaticoside in cosmetics, which involves optimizing the SERS enhancement effect through screening AgNPs with multiple morphologies and combining it with an Au@AgNPs-PDMS solid-state film platform. This invention addresses the shortcomings of existing technologies by providing a method for preparing an Au@AgNPs-PDMS film SERS detection platform and its application in the detection of asiaticoside in cosmetics. Summary of the Invention

[0006] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides an Au@AgNPs... The preparation method of the PDMS thin film SERS detection platform and its application in the detection of asiaticoside in cosmetics solve the problems mentioned in the background art.

[0007] (II) Technical Solution This invention addresses the deficiencies and needs in existing technologies by providing a method for preparing an Au@AgNPs-PDMS thin-film SERS detection platform and its application in the detection of asiaticoside in cosmetics.

[0008] In a first aspect, the present invention provides a method for preparing an Au@AgNPs-PDMS thin film SERS detection platform, comprising the following steps: S100. Silver nanoparticles (AgNPs) with three different morphologies—spherical, flower-like, and hexagonal—were prepared. The morphology and physicochemical properties were characterized by UV-Vis absorption spectroscopy and scanning electron microscopy (SEM). Using asiaticoside as the target compound, the SERS enhancement performance of the three morphologies of AgNPs was compared, and the nanostructure with the best enhancement effect was screened out for subsequent preparation and optimization of Au@Ag core-shell structures. S200. Au@Ag core-shell nanoparticles were prepared by seed growth method. Au nanoparticle AuNPs seed sol was first prepared by sodium citrate reduction method. Then, with AuNPs as the core, a silver shell layer was reduced and grown on its surface to prepare Au@AgNPs sol with Au core and Ag shell structure. S300. The cured PDMS film is subjected to plasma hydrophilization treatment to introduce active hydroxyl groups on the surface; then, it is modified by silanization with 3-aminopropyltrimethoxysilane APTMS to graft active amino groups onto the film surface to obtain an aminated modified PDMS film. S400. The aminated PDMS film is immersed in Au@AgNPs sol. Through the strong chemical interaction between Ag and amino groups, Au@AgNPs are uniformly self-assembled on the surface of the PDMS film. After assembly, the film is removed, unbound nanoparticles are cleaned and removed, and then dried to obtain the Au@AgNPs-PDMS film SERS detection platform.

[0009] Furthermore, the specific preparation methods for the three morphologies of AgNPs in step S100 are as follows: Preparation of spherical AgNPs: 4 mg AgNO3 was dissolved in 25 mL of ultrapure water to prepare AgNO3 solution; 5 mg NaBH4 was dissolved in 75 mL of ultrapure water and prepared fresh for use; under magnetic stirring at 500 r / min, the AgNO3 solution was added dropwise to the NaBH4 solution at a uniform rate. After the addition was completed, the reaction was continued at room temperature for 90 min to obtain bright yellow spherical AgNPs sol, which was stored at 4℃ in the dark. Preparation of flower-shaped AgNPs: 0.2 mL of 1 mol / L AgNO3 solution and 2 mL of 1% polyvinylpyrrolidone (PVP) solution were added sequentially to 10 mL of deionized water. After stirring magnetically at 500 rpm at room temperature until homogeneous, 1 mL of 0.1 mol / L ascorbic acid solution was quickly added, and stirring was continued for 15 min until the reaction was complete and the solution turned grayish-green. The reaction solution was transferred to a 50 mL centrifuge tube and centrifuged at 5000 rpm for 10 min. The supernatant was discarded, and the precipitate was washed three times with deionized water. Finally, it was redissolved in 10 mL of deionized water to obtain the flower-shaped AgNPs solution, which was stored at 4 °C in the dark. Preparation of hexagonal AgNPs: Under light-protected and room temperature conditions, 21.74 mL of ultrapure water, 50 μL of 0.05 M AgNO3 solution, 500 μL of 75 mM sodium citrate solution, and 2.5 mL of 0.7 mM MPVP solution (Mw = 29000 g / mol) were added sequentially to an Erlenmeyer flask, and the mixture was stirred vigorously for 1 min. 60 μL of 30 wt% H2O2 was added rapidly, and after standing for 3 min, 250 μL of 0.1 M NaBH4 solution was added rapidly. The reaction was stopped when the solution turned blue, yielding a hexagonal AgNPs solution, which was stored at 4 °C in the dark.

[0010] Further, the specific preparation method of Au@AgNPs in step S200 is as follows: 99 mL of ultrapure water and 1 mL of 1% chloroauric acid solution are added to a clean three-necked flask, and heated to boiling on an electromagnetic stirrer while maintaining magnetic stirring at 600 r / min; 1.5 mL of 1% sodium citrate solution is quickly added, and the mixture is continuously heated under reflux for 15 to 20 min until the solution turns wine red, thus obtaining AuNPs seed sol; 50 mL of the above AuNPs seed sol is taken, and 150 mL of ultrapure water and 2 mL of 1% sodium citrate solution are added, and the mixture is heated to boiling while maintaining stirring at 600 r / min; 2 mg of silver nitrate is weighed and dissolved in 1 mL of ultrapure water, and quickly added dropwise to the boiling solution, and the mixture is continuously boiled under reflux for 30 to 40 min; heating is stopped, and stirring is maintained until the solution cools to room temperature, and the volume is adjusted to 200 mL with ultrapure water to obtain Au@AgNPs sol, which is stored at 4°C protected from light.

[0011] Further, the specific method for PDMS film pretreatment in step S300 is as follows: Mix PDMS prepolymer according to the mass ratio of main agent to curing agent of 10:1, stir thoroughly and then degas under vacuum for 30 minutes. After removing the bubbles, pour it into a horizontally placed glass petri dish, control the thickness to be about 1 mm, cure in an 80℃ oven for 2 hours, cool to room temperature, peel off, and cut into 1 cm × 1 cm square films; treat the cut PDMS film with a plasma cleaner at 30W for 10 minutes to introduce active hydroxyl groups on the surface; immerse the hydrophilicized PDMS film in a 5% (v / v) APTMS anhydrous ethanol solution, shake on a shaker at room temperature overnight, remove and wash three times each with anhydrous ethanol and ultrapure water to remove unbound APTMS, blow dry with nitrogen to obtain a surface-aminated PDMS film, which is prepared and used immediately.

[0012] Furthermore, the self-assembly time in step S400 is 4 hours. After assembly, the film surface is rinsed three times with ultrapure water to remove unbonded nanoparticles. It is then air-dried at room temperature in the dark and stored at 4°C in the dark for later use.

[0013] Secondly, this invention provides the application of the above-mentioned Au@AgNPs-PDMS thin-film SERS detection platform in the detection of asiaticoside in cosmetics, specifically including the following steps: S500. Sample pretreatment of cosmetics: Accurately weigh the cosmetic sample to be tested, place it in a centrifuge tube, add ethanol-water solution, vortex to mix, centrifuge, take the supernatant and filter it through an organic filter membrane to obtain the test solution. S600, SERS spectral acquisition: The test droplet was placed on the surface of the Au@AgNPs-PDMS thin film SERS detection platform, incubated at room temperature and then air-dried. The SERS spectrum was acquired using a laser confocal Raman spectrometer. S700 Qualitative Identification: Based on the characteristic Raman peak position of asiaticoside, combined with a pre-established OPLS-DA or LDA qualitative identification model, determine whether the sample contains asiaticoside. S800 Quantitative detection: Based on the intensity of the characteristic Raman peak of asiaticoside, the content of asiaticoside in the sample is calculated by substituting it into the pre-established quantitative calibration model.

[0014] Furthermore, the method for establishing the qualitative identification model and the quantitative correction model in steps S700 and S800 is as follows: prepare a series of standard solutions of asiaticoside at different concentrations, acquire SERS spectra using the above-mentioned detection platform, and after baseline correction, Savitzky-Golay smoothing, and normalization preprocessing, establish a qualitative discrimination model using OPLS-DA and LDA; and establish a linear quantitative correction model with the intensity of the characteristic Raman peak of asiaticoside as the response value and the logarithm of concentration as the independent variable.

[0015] Further, in step S500, the volume fraction of the ethanol-water solution is 50%, the vortex mixing time is 10 min, the centrifugation speed is 8000 r / min, the centrifugation time is 10 min, and the pore size of the organic filter membrane is 0.22 μm.

[0016] Furthermore, the parameters of the laser confocal Raman spectrometer described in step S600 are set as follows: excitation wavelength 532nm, laser power 4.25mW, 100x objective lens, integration time 30s, integration 3 times, spectral scanning range 400 to 1800cm-1, and resolution 1cm-1.

[0017] Furthermore, the characteristic Raman peak position of asiaticoside mentioned in step S700 is the characteristic peak at 1320 cm⁻¹. Based on this peak position, the OPLS-DA model is established, and the cumulative explained rate of the model is R²Xcum greater than or equal to 0.99, R²Ycum greater than or equal to 0.99, and Q²cum greater than or equal to 0.98.

[0018] Furthermore, the quantitative correction model described in step S800 is a linear equation. Within the concentration range of 0.01 to 0.5 mg / mL, the characteristic peak intensity of asiaticoside at 1320 cm⁻¹ is taken as the response value y, and the logarithm of the asiaticoside concentration is taken as the independent variable x. The linear equation is y = 2865.7x + 124.8, and the correlation coefficient R² is greater than or equal to 0.998.

[0019] Furthermore, the room temperature incubation time in step S600 is 5 minutes, and SERS spectral acquisition is performed after natural air drying.

[0020] Furthermore, the assembly density of Au@AgNPs on the PDMS film surface in step S400 is adjusted by controlling the self-assembly time, which ranges from 2 to 6 hours. After self-assembly, the film surface exhibits a uniform silver-gold luster.

[0021] Furthermore, the screening and evaluation index for the three types of AgNPs in step S100 is the intensity of the characteristic Raman peak of asiaticoside. Based on the characteristic peak intensity of flower-shaped AgNPs, the characteristic peak intensity of spherical AgNPs is about one-seventh that of flower-shaped AgNPs, and the characteristic peak intensity of hexagonal AgNPs is about four-tenths that of flower-shaped AgNPs. Flower-shaped AgNPs are selected for subsequent optimization and preparation of Au@Ag core-shell structures.

[0022] Furthermore, the enhancement factor of the Au@Ag core-shell nanoparticles in step S200 is 6.73×103. A silver shell layer is reduced and grown on the surface of AuNPs by seed growth method, and the thickness of the shell layer is controlled by the amount of silver nitrate added.

[0023] Furthermore, in step S300, the power of the plasma hydrophilization treatment is 30W, the treatment time is 10min, and the contact angle of the PDMS film surface is reduced to below 20 degrees after treatment; the concentration of APTMS silanization modification is 5% by volume, the treatment time is 12 to 16h, and the amino density of the PDMS film surface after treatment is 0.5 to 1.5μmol per square centimeter.

[0024] Further, in step S500, the sample amount of the cosmetic sample to be tested is 0.5g, the volume of the added ethanol-water solution is 5mL, and the mass-volume ratio of the sample to the solvent is 1g:10mL.

[0025] Furthermore, the LDA qualitative identification model described in step S700 has a discrimination accuracy of 100%, which can accurately distinguish asiaticoside from other functional ingredients and matrix interferences in cosmetics.

[0026] Furthermore, the detection limit of the method described in step S800 is 25 nM, calculated according to the 3σ / k formula, and exhibits good linearity in the concentration range of 0.01 to 0.5 mg / mL.

[0027] Furthermore, the Au@AgNPs-PDMS thin film SERS detection platform of the present invention is stored at 4°C in the dark, with a storage validity period of 3 months, and the relative standard deviation (RSD) of parallel detection is less than 5%.

[0028] Furthermore, the method for the spiked recovery experiment described in this invention is as follows: Three concentrations of asiaticoside standard (low, medium, and high) are added to a cosmetic blank matrix that does not contain asiaticoside. The low concentration is 0.02 μM, the medium concentration is 0.1 μM, and the high concentration is 0.2 μM. The sample is processed and detected according to steps S500 to S800. Each concentration is performed in parallel six times. The spiked recovery rate is calculated to be 82.3% to 90.7%, and the relative standard deviation (RSD) is 3.56% to 4.83%.

[0029] Furthermore, the detection time for a single sample in step S600 is within 10 minutes, including 3 minutes for sample pretreatment, 2 minutes for SERS spectral acquisition, and 5 minutes for data analysis.

[0030] Furthermore, in the preparation method of the Au@AgNPs-PDMS thin film SERS detection platform of the present invention, the particle size range of spherical AgNPs is 20 to 50 nm, the particle size range of flower-shaped AgNPs is 200 to 500 nm, and the particle size range of hexagonal AgNPs is 100 to 300 nm.

[0031] Furthermore, in the Au@AgNPs core-shell structure of the present invention, the Au core has a particle size range of 15 to 25 nm, and the Ag shell has a thickness range of 5 to 15 nm.

[0032] Furthermore, the thickness of the PDMS film of the present invention ranges from 0.5 to 2 mm, preferably 1 mm, and the film size is 1 cm × 1 cm, but it can also be cut to other sizes according to actual testing requirements.

[0033] Furthermore, the Au@AgNPs-PDMS thin film SERS detection platform described in this invention is reusable. After use, the surface can be rinsed with ultrapure water three times, dried at room temperature, and then reused. It can be reused more than 10 times without significant performance degradation.

[0034] Furthermore, in the OPLS-DA qualitative identification model of the present invention, the sample categories include asiaticoside standard, asiaticoside added cosmetic group, cosmetic blank matrix group, and interference group. The interference group includes common cosmetic matrix ingredients such as glycerin, propylene glycol, niacinamide, and sodium hyaluronate.

[0035] Furthermore, the SERS characteristic peaks of asiaticoside described in this invention are assigned as follows: 1320 cm⁻¹ is the COC stretching vibration peak, 1070 cm⁻¹ is the CO stretching vibration peak, 860 cm⁻¹ is the CH out-of-plane bending vibration peak, and 480 cm⁻¹ is the OH bending vibration peak.

[0036] Furthermore, in the preparation method of the Au@AgNPs-PDMS thin film SERS detection platform of the present invention, the time interval between steps S100 and S200 shall not exceed 2 hours to maintain the activity of nanoparticles; the PDMS thin film after step S300 treatment needs to be assembled within 24 hours to avoid the reduction of amino activity.

[0037] Furthermore, in the preparation of the flower-like AgNPs of the present invention, PVP acts as a morphology guiding agent and dispersant, ascorbic acid acts as a reducing agent, and the mass ratio of PVP to AgNO3 during the reaction is 1:1 to 2:1.

[0038] Furthermore, in the preparation of the hexagonal AgNPs described in this invention, H2O2 acts as an oxidant to regulate the morphology of the nanoparticles, NaBH4 acts as a strong reducing agent to initiate the reaction and control the particle size, and PVP acts as a surfactant to prevent particle aggregation.

[0039] Furthermore, the application of the Au@AgNPs-PDMS thin film SERS detection platform described in this invention in online quality control during cosmetic production includes four steps: sampling, pretreatment, SERS detection, and data analysis, enabling real-time monitoring of asiaticoside content during the production process.

[0040] Furthermore, the application of the Au@AgNPs-PDMS thin-film SERS detection platform described in this invention in rapid on-site testing for market supervision includes three steps: sample collection, portable SERS detection, and on-site interpretation, enabling rapid screening of asiaticoside content in cosmetics.

[0041] Furthermore, the portable SERS detection device of the present invention uses a 532nm excitation light source, the laser power is adjustable from 1 to 10mW, and is equipped with a portable data processing terminal, which can realize real-time transmission of on-site data and model interpretation.

[0042] Furthermore, the verification method of the quantitative calibration model of the present invention is as follows: take 10 standard solutions of asiaticoside with known concentrations, covering a concentration range of 0.01 to 0.5 mg / mL, use the method of the present invention to detect them, calculate the relative error between the predicted value and the true value, and the relative error is less than 10%.

[0043] Furthermore, the verification method of the qualitative identification model of the present invention is as follows: take 20 positive samples and 20 negative samples of asiaticoside, and use the method of the present invention to detect them. Calculate the sensitivity, specificity and accuracy of the model. The sensitivity is greater than or equal to 98%, the specificity is greater than or equal to 98%, and the accuracy is greater than or equal to 98%.

[0044] Furthermore, the method described in this invention can also be extended to the detection of other cosmetic active ingredients, such as dipotassium glycyrrhizate, ceramide, squalane, etc., simply by replacing the corresponding standard to establish the corresponding qualitative and quantitative model.

[0045] Furthermore, in step S100 of the present invention, the SERS enhancement performance comparison of the three morphologies of AgNPs is performed using a standard solution of asiaticoside with the same concentration of 10 μM to eliminate the interference of concentration factors on the evaluation of the enhancement effect.

[0046] Furthermore, in step S100 of the present invention, the selected flower-like AgNPs have a multi-level protrusion structure, high roughness, and abundant interparticle gaps, which can form a large number of SERS hot spots, making them the nanostructures with the best enhancement effect.

[0047] Furthermore, in step S200 of the present invention, the Au@Ag core-shell structure combines the chemical stability of the Au core with the high SERS enhancement performance of the Ag shell, while overcoming the disadvantage of easy oxidation of pure AgNPs and improving the service life of the detection platform.

[0048] Furthermore, in step S300 of the present invention, plasma hydrophilization treatment introduces hydroxyl groups on the PDMS surface, and APTMS silanization modification introduces amino groups on the basis of hydroxyl groups. The two-step treatment realizes the regulation of the chemical properties of the PDMS surface, providing active sites for the subsequent assembly of nanoparticles.

[0049] Furthermore, in step S400 of the present invention, the strong chemical interaction between Ag and amino groups includes coordination and electrostatic interactions. The lone pair electrons of the amino group form coordination bonds with Ag, thereby achieving a strong bond between Au@AgNPs and the PDMS film surface.

[0050] Furthermore, in step S500 of the present invention, the role of the ethanol-water solution is to break the emulsion and extract asiaticoside from cosmetics, and the extraction efficiency of asiaticoside by a 50% ethanol solution is over 90%.

[0051] Furthermore, in step S600 of the present invention, the purpose of room temperature incubation is to allow asiaticoside molecules to be fully adsorbed onto the surface hot spot area of ​​the SERS detection platform, and an incubation time of 5 minutes can reach adsorption equilibrium.

[0052] Furthermore, in step S700 of the present invention, the OPLS-DA model is validated using cross-validation, specifically leave-one-out cross-validation, to ensure the reliability and generalization ability of the model.

[0053] Furthermore, in step S800 of the present invention, the quantitative calibration model uses the least squares method for regression analysis, and the predictive ability of the model is evaluated through cross-validation.

[0054] Furthermore, the characterization methods of the Au@AgNPs-PDMS thin film SERS detection platform of the present invention include: ultraviolet-visible absorption spectroscopy for characterizing the plasmon resonance characteristics of nanoparticles, scanning electron microscopy (SEM) for characterizing the morphology and particle size of nanoparticles, transmission electron microscopy (TEM) for characterizing the Au@Ag core-shell structure, X-ray photoelectron spectroscopy (XPS) for characterizing the elemental composition and chemical state, and a contact angle meter for characterizing the hydrophilicity and hydrophobicity of the PDMS thin film surface.

[0055] Furthermore, application examples of the method described in this invention in actual cosmetic sample testing include: the content of asiaticoside in the asiaticoside essence is 1.28%, consistent with the content on the product label; the content of asiaticoside in the soothing toner is 0.08%, consistent with the content on the product label; and asiaticoside was not detected in the moisturizing cream, consistent with the formula.

[0056] Furthermore, in the spiked recovery experiment, the method of the present invention achieved a recovery rate of 82.3% and an RSD of 4.83% at a low concentration of 0.02 μM; a recovery rate of 86.5% and an RSD of 4.12% at a medium concentration of 0.1 μM; and a recovery rate of 90.7% and an RSD of 3.56% at a high concentration of 0.2 μM.

[0057] Compared with the prior art, the present invention provides an Au@AgNPs The preparation method of the PDMS thin film SERS detection platform and its application in the detection of asiaticoside in cosmetics have the following beneficial effects: 1. Significantly improved detection sensitivity: This invention clarifies the influence of nanomorphology on SERS enhancement by controllable preparation and systematic screening of AgNPs with three morphologies: spherical, flower-shaped, and hexagonal. The flower-shaped AgNPs with the best enhancement effect are selected for core-shell structure optimization, which can reduce the detection limit of asiaticoside to the nM level, which is far superior to traditional spherical nanoparticle substrates.

[0058] 2. Excellent platform stability and reproducibility: The Au@AgNPs constructed in this invention The PDMS solid-state thin film SERS testing platform solves the problems of poor storage stability and insufficient batch-to-batch reproducibility of traditional liquid precious metal sols. It shows no significant performance degradation after 3 months of storage at 4°C in the dark, and the relative standard deviation (RSD) of parallel tests is less than 5%, meeting the stability requirements of actual testing.

[0059] 3. Strong anti-interference ability and high detection accuracy: This invention combines OPLS-DA and LDA chemometric methods to establish a qualitative and quantitative model, which can effectively eliminate the interference of complex matrices such as oils, moisturizers, and preservatives in cosmetics, and achieve accurate differentiation of asiaticoside from other active ingredients and matrix interferences. The spiked recovery rate is 92.3%~105.7%, and the detection results are accurate and reliable.

[0060] 4. Highly practical and adaptable to rapid on-site testing: The detection platform of this invention has a simple preparation process and low cost. Sample pretreatment is simple, and the testing of a single sample can be completed within 10 minutes. It does not require large precision instruments or professional operators. It can be adapted to various application scenarios such as online quality control in cosmetic production and rapid on-site screening in market supervision, and has good prospects for industrial application. Attached Figure Description

[0061] Figure 1 This invention relates to Au@AgNPs Schematic diagram of the preparation process of the PDMS thin film SERS detection platform; Figure 2 The figures show the characterization results of three different morphologies of AgNPs in this invention. Figure 2 A is the ultraviolet-visible absorption spectrum. Figure 2 B is a SEM image of the flower-like AgNPs. Figure 2 C is the SEM image of hexagonal AgNPs. Figure 2 D is the SEM image of spherical AgNPs; Figure 3 The SERS characteristic spectrum and characteristic peak assignment of the asiaticoside standard of this invention; Figure 4 Score map of the qualitative identification model of asiaticoside based on OPLS-DA; Figure 5 This is a linear quantitative calibration curve of the concentration of asiaticoside and the intensity of the characteristic peak in this invention. Detailed Implementation

[0062] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and 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.

[0063] Please see the appendix Figure 1-5 This invention provides a method for preparing an Au@AgNPs-PDMS thin-film SERS detection platform and its application in the detection of asiaticoside in cosmetics. The technical solution of this invention will be described in detail below with reference to specific embodiments.

[0064] Firstly, please refer to the appendix. Figure 1 Specifically, this invention relates to a method for preparing an Au@AgNPs-PDMS thin film SERS detection platform, comprising the following steps: Step S100: Prepare three types of silver nanoparticles (AgNPs) with different morphologies and screen them for SERS enhancement performance. Step S200: Au@Ag core-shell nanoparticles are prepared using a seed growth method; Step S300: Plasma hydrophilization treatment and APTMS silanization modification are performed on the PDMS film; Step S400: Au@AgNPs are self-assembled onto the surface of the aminated PDMS film.

[0065] The specific preparation methods for the three morphologies of AgNPs in step S100 are as follows: Preparation of spherical AgNPs: 4 mg of AgNO3 was dissolved in 25 mL of ultrapure water to prepare an AgNO3 solution; 5 mg of NaBH4 was dissolved in 75 mL of ultrapure water, prepared fresh each time; under magnetic stirring at 500 r / min, the AgNO3 solution was added dropwise to the NaBH4 solution at a uniform rate. After the addition was complete, the reaction was continued at room temperature for 90 min to obtain a bright yellow spherical AgNP sol, which was stored at 4℃ in the dark. The particle size range of the spherical AgNPs prepared by the above method was 20 to 50 nm.

[0066] Preparation of flower-shaped AgNPs: 0.2 mL of 1 mol / L AgNO3 solution and 2 mL of 1% (w / w) polyvinylpyrrolidone (PVP) solution were added sequentially to 10 mL of deionized water. The mixture was magnetically stirred at 500 rpm at room temperature until homogeneous. Then, 1 mL of 0.1 mol / L ascorbic acid solution was quickly added, and stirring continued for 15 min until the reaction was complete and the solution turned grayish-green. The reaction solution was transferred to a 50 mL centrifuge tube and centrifuged at 5000 rpm for 10 min. The supernatant was discarded, and the precipitate was washed three times with deionized water and finally redissolved in 10 mL of deionized water to obtain the flower-shaped AgNPs solution. The solution was stored at 4°C protected from light. The particle size range of the flower-shaped AgNPs prepared by the above method was 200 to 500 nm. PVP was used as a morphology directing agent and dispersant in the reaction, and the mass ratio of PVP to AgNO3 was controlled within the range of 1:1 to 2:1. Ascorbic acid was used as a reducing agent.

[0067] Preparation of hexagonal AgNPs: Under light-protected and room temperature conditions, 21.74 mL of ultrapure water, 50 μL of 0.05 M AgNO3 solution, 500 μL of 75 mM sodium citrate solution, and 2.5 mL of 0.7 mM PVP solution (weight-average molecular weight 29000 g / mol) were added sequentially to an Erlenmeyer flask, and the mixture was stirred vigorously for 1 min. Then, 60 μL of 30 wt% H2O2 was quickly added, and after standing for 3 min, 250 μL of 0.1 M NaBH4 solution was quickly added. The reaction was stopped when the solution turned blue, yielding a hexagonal AgNPs solution, which was stored at 4 °C in the dark. The particle size range of the hexagonal AgNPs prepared by the above method was 100 to 300 nm. H2O2 acted as an oxidant in the reaction, participating in the regulation of nanoparticle morphology; NaBH4 acted as a strong reducing agent, initiating the reaction and controlling particle size; and PVP acted as a surfactant, preventing particle aggregation.

[0068] Please see the appendix Figure 2 Three morphologies of AgNPs were characterized and their SERS enhancement performance was evaluated: Absorption curves were measured using UV-Vis absorption spectroscopy. Spherical AgNPs showed a characteristic absorption peak near 400 nm, flower-like AgNPs had a broad absorption band in the range of 420 to 450 nm, and hexagonal AgNPs had an absorption peak near 420 nm. Morphology was observed using scanning electron microscopy (SEM). Spherical AgNPs were uniformly spherical, flower-like AgNPs had a multi-level protrusion structure, and hexagonal AgNPs were regular hexagons. SERS performance was tested using asiaticoside as the target compound. The concentration of the asiaticoside standard solution was 10 μM. The parameters of the laser confocal Raman spectrometer were set as follows: excitation wavelength 532 nm, laser power 4.25 mW, 100x objective lens, integration time 30 s, integration 3 times, spectral scanning range 400 to 1800 cm⁻¹, and resolution 1 cm⁻¹. Comparing the characteristic peak intensities of flower-shaped AgNPs to those of flower-shaped AgNPs, the characteristic peak intensities of spherical AgNPs are approximately one-seventh that of flower-shaped AgNPs, and those of hexagonal AgNPs are approximately four-tenths that of flower-shaped AgNPs. Flower-shaped AgNPs, due to their multi-level protrusion structure, high roughness, and abundant interparticle gaps, can form numerous SERS hotspots, thus exhibiting the best enhancement effect. Therefore, flower-shaped AgNPs were selected for the subsequent optimized fabrication of Au@Ag core-shell structures.

[0069] The specific preparation method of Au@Ag core-shell nanoparticles in step S200 is as follows: 99 mL of ultrapure water and 1 mL of 1% chloroauric acid solution were added to a clean three-necked flask and heated to boiling on a magnetic stirrer while maintaining magnetic stirring at 600 rpm. 1.5 mL of 1% sodium citrate solution was quickly added, and the mixture was heated under reflux for 15 to 20 minutes until the solution turned wine-red, thus obtaining the AuNPs seed sol. The Au nuclei in the AuNPs seed sol had a particle size range of 15 to 25 nm.

[0070] Take 50 mL of the above AuNPs seed sol, add 150 mL of ultrapure water and 2 mL of 1% sodium citrate solution, heat to boiling and maintain stirring at 600 rpm; weigh 2 mg of silver nitrate and dissolve it in 1 mL of ultrapure water, then quickly add it dropwise to the boiling solution, and continue boiling and reflux for 30 to 40 min; stop heating, keep stirring until the solution cools to room temperature, and make up to 200 mL with ultrapure water to obtain Au@AgNPs sol, which is stored at 4℃ in the dark. A silver shell layer is reduced and grown on the surface of AuNPs using the seed growth method. The shell thickness is controlled by the amount of silver nitrate added, and the Ag shell thickness ranges from 5 to 15 nm.

[0071] Characterization of Au@AgNPs: Plasmon resonance characteristics were characterized by UV-Vis absorption spectroscopy, and Au@AgNPs showed obvious plasmon resonance peaks in the range of 400 to 500 nm; the core-shell structure was characterized by transmission electron microscopy (TEM), and obvious Au cores and Ag shells were observed; the elemental composition and chemical state were characterized by X-ray photoelectron spectroscopy (XPS), confirming the presence of Au and Ag elements; the enhancement factor of Au@Ag core-shell nanoparticles was calculated to be 6.73 × 10³.

[0072] The specific method for PDMS film pretreatment in step S300 is as follows: Mix the PDMS prepolymer with the main agent and curing agent at a mass ratio of 10:1, stir thoroughly, and then degas under vacuum for 30 minutes. After removing air bubbles, pour the mixture into a horizontally placed glass petri dish, controlling the thickness to be approximately 1 mm. Cure in an oven at 80°C for 2 hours. After cooling to room temperature, peel off the film and cut it into 1 cm × 1 cm square films. The thickness of the PDMS film ranges from 0.5 to 2 mm, preferably 1 mm, but it can also be cut to other sizes according to actual testing requirements.

[0073] The cut PDMS film was treated with a 30W plasma cleaner for 10 minutes to introduce active hydroxyl groups on the surface. After treatment, the contact angle of the PDMS film surface was reduced to below 20 degrees.

[0074] The hydrophilicated PDMS film was immersed in a 5% (v / v) APTMS anhydrous ethanol solution and shaken overnight at room temperature for 12 to 16 hours. After removal, it was washed three times each with anhydrous ethanol and ultrapure water to remove unbound APTMS, and then dried under nitrogen to obtain an aminated PDMS film, which was prepared and used immediately. The amino density on the surface of the treated PDMS film was 0.5 to 1.5 μmol / cm². The treated PDMS film needed to be assembled within 24 hours to avoid a decrease in amino activity.

[0075] The specific method for the self-assembly of Au@AgNPs on the PDMS film surface in step S400 is as follows: Aminated PDMS films were immersed in Au@AgNPs sol. Through the strong chemical interaction between Ag and amino groups, Au@AgNPs achieved uniform self-assembly on the PDMS film surface. The strong chemical interaction between Ag and amino groups includes coordination and electrostatic interactions; the lone pair electrons of the amino group form coordination bonds with Ag, resulting in a firm bond between Au@AgNPs and the PDMS film surface. The self-assembly time was 4 hours. After assembly, the film surface was rinsed three times with ultrapure water to remove unbonded nanoparticles, air-dried at room temperature in the dark, and stored at 4°C in the dark for later use. The assembly density of Au@AgNPs on the PDMS film surface was adjusted by controlling the self-assembly time, which ranged from 2 to 6 hours. After self-assembly, the film surface exhibited a uniform silver-gold luster.

[0076] The Au@AgNPs-PDMS thin film SERS detection platform was characterized: the plasmon resonance characteristics of the nanoparticles were characterized by UV-Vis absorption spectroscopy, with obvious plasmon resonance peaks in the range of 400 to 500 nm; the morphology and particle size of the nanoparticles were characterized by scanning electron microscopy (SEM), and Au@AgNPs were observed to be uniformly distributed on the PDMS film surface; the hydrophilicity and hydrophobicity of the PDMS film surface were characterized by contact angle measurement, with contact angle measurements ranging from 30 to 60 degrees; the film exhibited a uniform silver-gold luster and no obvious particle aggregation.

[0077] Secondly, the present invention specifically relates to the application of the above-mentioned Au@AgNPs-PDMS thin-film SERS detection platform in the detection of asiaticoside in cosmetics, including the following steps: Step S500: Sample pretreatment for cosmetics; Step S600: SERS spectral acquisition; Step S700: Qualitative identification; Step S800: Quantitative detection.

[0078] The specific method for pretreatment of cosmetic samples in step S500 is as follows: Accurately weigh 0.5 g of the cosmetic sample to be tested and place it in a centrifuge tube. Add 5 mL of 50% (v / v) ethanol-water solution, with a sample to solvent mass-to-volume ratio of 1 g:10 mL. Vortex to mix for 10 min, then centrifuge at 8000 r / min for 10 min. Filter the supernatant through a 0.22 μm organic filter membrane to obtain the test solution. The ethanol-water solution serves to demulsify and extract asiaticoside from the cosmetic. The extraction efficiency of asiaticoside using a 50% (v / v) ethanol solution is over 90%.

[0079] See appendix Figure 3 The specific method for SERS spectrum acquisition in step S600 is as follows: A droplet of the sample to be tested was added to the surface of the Au@AgNPs-PDMS thin-film SERS detection platform and incubated at room temperature for 5 minutes, then allowed to air dry. SERS spectra were acquired using a laser confocal Raman spectrometer with the following parameters: excitation wavelength 532 nm, laser power 4.25 mW, 100x objective lens, integration time 30 s, integration three times, spectral scanning range 400 to 1800 cm⁻¹, and resolution 1 cm⁻¹. Room temperature incubation was used to ensure that asiaticoside molecules were fully adsorbed onto the hot spot region of the SERS detection platform; an incubation time of 5 minutes was sufficient to reach adsorption equilibrium. The detection time for a single sample was less than 10 minutes, including 3 minutes for sample pretreatment, 2 minutes for SERS spectrum acquisition, and 5 minutes for data analysis.

[0080] Please see the appendix Figure 4 The specific method for qualitative identification in step S700 is as follows: Based on the characteristic Raman peak positions of asiaticoside, combined with a pre-established OPLS-DA or LDA qualitative identification model, it is determined whether the sample contains asiaticoside. The characteristic Raman peak positions of asiaticoside are: a characteristic peak at 1320 cm⁻¹, corresponding to the COC stretching vibration peak; a CO stretching vibration peak at 1070 cm⁻¹; an out-of-plane bending vibration peak at 860 cm⁻¹; and an OH bending vibration peak at 480 cm⁻¹.

[0081] Methods for establishing the OPLS-DA model: A series of asiaticoside standard solutions of various concentrations were prepared. SERS spectra were acquired using the aforementioned detection platform. After baseline correction, Savitzky-Golay smoothing, and normalization preprocessing, a qualitative discriminant model was established using OPLS-DA. The OPLS-DA model was established based on the characteristic peak at 1320 cm⁻¹. The cumulative explained values ​​of the model were R²Xcum ≥ 0.99, R²Ycum ≥ 0.99, and Q²cum ≥ 0.98. The OPLS-DA model was validated using cross-validation with leave-one-out cross-validation. Sample categories included asiaticoside standard, asiaticoside-added cosmetics, cosmetic blank matrix, and interference groups. The interference group included common cosmetic matrix ingredients such as glycerin, propylene glycol, niacinamide, and sodium hyaluronate.

[0082] The method for establishing the LDA model: A qualitative discrimination model is established using LDA. The discrimination accuracy of the LDA qualitative identification model is 100%, which can accurately distinguish asiaticoside from other functional ingredients and matrix interferences in cosmetics.

[0083] Please see the appendix Figure 5 The specific method for quantitative detection in step S800 is as follows: Based on the intensity of the characteristic Raman peak of asiaticoside, the content of asiaticoside in the sample was calculated by substituting it into a pre-established quantitative calibration model.

[0084] The quantitative calibration model was established as follows: A series of standard solutions of asiaticoside at various concentrations were prepared. SERS spectra were acquired using the aforementioned detection platform. After baseline correction, Savitzky-Golay smoothing, and normalization preprocessing, a linear quantitative calibration model was established with the intensity of the characteristic Raman peak of asiaticoside as the response value and the logarithm of the concentration as the independent variable. Within the concentration range of 0.01 to 0.5 mg / mL, the linear equation was y = 2865.7x + 124.8, with a correlation coefficient R² greater than or equal to 0.998. The quantitative calibration model was analyzed using the least squares regression method, and its predictive ability was evaluated through cross-validation.

[0085] The detection limit of the method is 25 nM, calculated according to the 3σ / k formula, and it exhibits good linearity in the concentration range of 0.01 to 0.5 mg / mL.

[0086] The technical effects of the present invention will be further illustrated below through specific embodiments and comparative examples.

[0087] Example 1 Spherical AgNPs were prepared according to step S100, Au@AgNPs were prepared according to step S200, and the Au@AgNPs-PDMS thin film SERS detection platform was prepared according to steps S300 and S400. Cosmetic sample pretreatment was performed according to step S500, SERS spectral acquisition was performed according to step S600, qualitative identification was performed according to step S700, and quantitative detection was performed according to step S800.

[0088] Ten standard solutions of asiaticoside with known concentrations, ranging from 0.01 to 0.5 mg / mL, were tested using the method of this invention. The relative error between the predicted and actual values ​​was calculated, and the relative error was less than 10%.

[0089] Twenty positive and twenty negative samples of asiaticoside were taken and detected using the method of this invention. The sensitivity, specificity and accuracy of the model were calculated. The sensitivity was greater than or equal to 98%, the specificity was greater than or equal to 98%, and the accuracy was greater than or equal to 98%.

[0090] Example 2 Spiking recovery experiments were conducted by adding low, medium, and high concentrations of asiaticoside standard to a cosmetic blank matrix that did not contain asiaticoside. The low concentration was 0.02 μM, the medium concentration was 0.1 μM, and the high concentration was 0.2 μM. The processing and detection were performed according to steps S500 to S800, and each concentration was repeated 6 times.

[0091] At a low concentration of 0.02 μM, the recovery rate was 82.3% with an RSD of 4.83%; at a medium concentration of 0.1 μM, the recovery rate was 86.5% with an RSD of 4.12%; and at a high concentration of 0.2 μM, the recovery rate was 90.7% with an RSD of 3.56%.

[0092] Example 3 The method of this invention was used to perform testing on actual cosmetic samples.

[0093] The Centella Asiatica extract contained 1.28% Centella Asiatica extract, consistent with the product label; the soothing toner contained 0.08% Centella Asiatica extract, consistent with the product label; and the moisturizing cream did not contain any Centella Asiatica extract, consistent with the formula.

[0094] Example 4 The prepared Au@AgNPs-PDMS thin-film SERS detection platform was stored at 4℃ in the dark for 3 months before performance verification. The SERS signal intensity attenuation was less than 10%, meeting the stability requirements for actual detection; the RSD of 10 detection platforms prepared in the same batch for the same concentration of asiaticoside standard solution was less than 5%, meeting the batch-to-batch reproducibility requirements.

[0095] The testing platform is reusable. After each use, rinse the surface with ultrapure water three times, let it air dry at room temperature, and then continue to use it. It can be reused more than 10 times without significant performance degradation.

[0096] The cost control method of the Au@AgNPs-PDMS thin film SERS detection platform of the present invention is as follows: the PDMS film uses commercial PDMS prepolymer, and the cost is less than 0.1 yuan per piece; the Au@AgNPs sol is prepared using low-concentration chloroauric acid and silver nitrate, and the raw material cost is controllable; the preparation cost of a single detection platform is less than 10 yuan, which is suitable for large-scale promotion and application.

[0097] The method described in this invention, when applied to online quality control in cosmetic production, includes four steps: sampling, pretreatment, SERS detection, and data analysis, enabling real-time monitoring of asiaticoside content during production. It features short detection time (less than 10 minutes for a single sample), simple sample pretreatment (no complex extraction and purification steps required), portable instrumentation for on-site testing in the production workshop, and low cost, making it suitable for large-scale screening.

[0098] The method described in this invention, when applied to rapid on-site testing in market supervision, includes three steps: sample collection, portable SERS detection, and on-site interpretation, enabling rapid screening of asiaticoside content in cosmetics. It features fast detection speed, with results available in less than 15 minutes from sampling; simple operation, requiring no professional training; intuitive results, with qualitative interpretation automatically output by a model; and traceable data, with test data uploaded to the regulatory platform in real time.

[0099] The method described in this invention has the following potential applications: raw material inspection upon arrival at cosmetic manufacturing enterprises, production process control, and finished product inspection upon leaving the factory; random inspection and screening by cosmetic regulatory authorities and market circulation supervision; and formula screening and efficacy evaluation by cosmetic research and development institutions.

[0100] The method described in this invention can also be extended to the detection of other cosmetic active ingredients, such as dipotassium glycyrrhizate, ceramide, squalane, etc., simply by replacing the corresponding standard to establish the corresponding qualitative and quantitative model.

[0101] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An Au@AgNPs A method for preparing a PDMS thin film SERS detection platform, characterized in that, Includes the following steps: S100: Silver nanoparticles (AgNPs) with three different morphologies—spherical, flower-like, and hexagonal—were prepared respectively. Using asiaticoside as the target compound, the SERS enhancement performance of the three morphologies of AgNPs was compared, and the nanostructure with the best enhancement effect was screened. S200: Au@Ag core-shell nanoparticles were prepared by seed growth method. Au nanoparticle AuNPs seed sol was first prepared by sodium citrate reduction method. Then, with AuNPs as the core, a silver shell layer was reduced and grown on its surface to prepare Au@AgNPs sol with Au core and Ag shell structure. S300: The cured PDMS film is subjected to plasma hydrophilization treatment to introduce active hydroxyl groups on the surface; then, it is modified by silanization with 3-aminopropyltrimethoxysilane APTMS to graft active amino groups onto the film surface to obtain an aminated modified PDMS film. S400: The aminated PDMS film is immersed in Au@AgNPs sol. Through the chemical interaction between Ag and amino groups, Au@AgNPs are uniformly self-assembled on the surface of the PDMS film. After assembly, the film is removed, unbound nanoparticles are cleaned and removed, and then dried to obtain the Au@AgNPs-PDMS film SERS detection platform.

2. An Au@AgNPs according to claim 1 A method for preparing a PDMS thin film SERS detection platform, characterized in that, The specific preparation methods for the three morphologies of AgNPs mentioned in step S100 are as follows: Preparation of spherical AgNPs: 4 mg AgNO3 was dissolved in 25 mL of ultrapure water to prepare AgNO3 solution; 5 mg NaBH4 was dissolved in 75 mL of ultrapure water; under magnetic stirring at 500 r / min, the AgNO3 solution was added dropwise to the NaBH4 solution at a uniform rate. After the addition was completed, the reaction was continued at room temperature for 90 min to obtain bright yellow spherical AgNPs sol. Preparation of flower-like AgNPs: 0.2 mL of 1 mol / L AgNO3 solution and 2 mL of 1% (w / w) polyvinylpyrrolidone (PVP) solution were added to 10 mL of deionized water. After stirring magnetically at 500 r / min at room temperature until homogeneous, 1 mL of 0.1 mol / L ascorbic acid solution was quickly added. The mixture was stirred for 15 min until the reaction was complete. The reaction solution was centrifuged, and the precipitate was washed three times with deionized water. Finally, it was redissolved in 10 mL of deionized water to obtain the flower-like AgNPs solution. Preparation of hexagonal AgNPs: Under light-protected and room temperature conditions, 21.74 mL of ultrapure water, 50 μL of 0.05 M AgNO3 solution, 500 μL of 75 mM sodium citrate solution, and 2.5 mL of 0.7 mM MPV solution were added sequentially to an Erlenmeyer flask, and the mixture was stirred vigorously for 1 min. 60 μL of 30 wt% H2O2 was added quickly, and after standing for 3 min, 250 μL of 0.1 M NaBH4 solution was added quickly. The reaction was stopped when the solution turned blue, yielding a hexagonal AgNPs solution.

3. An Au@AgNPs according to claim 1 A method for preparing a PDMS thin film SERS detection platform, characterized in that, The specific preparation method of Au@AgNPs in step S200 is as follows: 99 mL of ultrapure water and 1 mL of 1% chloroauric acid solution are added to a clean three-necked flask, and heated to boiling on an electromagnetic stirrer while maintaining magnetic stirring at 600 r / min; 1.5 mL of 1% sodium citrate solution is quickly added, and the mixture is heated under reflux for 15 to 20 min until the solution turns wine red, thus obtaining AuNPs seed sol; 50 mL of the above AuNPs seed sol is taken, and 150 mL of ultrapure water and 2 mL of 1% sodium citrate solution are added, and the mixture is heated to boiling while maintaining stirring at 600 r / min; 2 mg of silver nitrate is weighed and dissolved in 1 mL of ultrapure water, and quickly added dropwise to the boiling solution, and the mixture is boiled under reflux for 30 to 40 min; heating is stopped, and stirring is maintained until the solution cools to room temperature, and the volume is adjusted to 200 mL with ultrapure water to obtain Au@AgNPs sol.

4. An Au@AgNPs according to claim 1 A method for preparing a PDMS thin film SERS detection platform, characterized in that, The specific method for PDMS film pretreatment in step S300 is as follows: Mix PDMS prepolymer according to the mass ratio of main agent to curing agent of 10:1, stir thoroughly and then degas under vacuum for 30 minutes. After removing the bubbles, pour the mixture into a horizontally placed glass petri dish, control the thickness to be about 1 mm, cure in an oven at 80℃ for 2 hours, cool to room temperature, peel off, and cut into 1 cm × 1 cm square films; treat the cut PDMS film with a plasma cleaner at 30 W for 10 minutes to introduce active hydroxyl groups on the surface; immerse the hydrophilicized PDMS film in a 5% (v / v) APTMS anhydrous ethanol solution, shake on a shaker at room temperature overnight, remove and wash three times each with anhydrous ethanol and ultrapure water, and dry with nitrogen to obtain an aminated PDMS film.

5. An Au@AgNPs according to claim 1 The preparation of a PDMS thin film SERS detection platform is characterized by, The self-assembly time in step S400 is 4 hours. After assembly, the film surface is rinsed three times with ultrapure water to remove unbonded nanoparticles, and then air-dried at room temperature in the dark.

6. An Au@AgNPs The application of the PDMS thin-film SERS detection platform in the detection of asiaticoside in cosmetics is characterized by, Includes the following steps: S500: Sample pretreatment of cosmetics: Accurately weigh the cosmetic sample to be tested, place it in a centrifuge tube, add ethanol-water solution, vortex to mix, centrifuge, take the supernatant and filter it through an organic filter membrane to obtain the test solution; S600: SERS spectral acquisition: The test droplet is placed on the surface of the Au@AgNPs-PDMS thin film SERS detection platform, incubated at room temperature and then air-dried. The SERS spectrum is acquired using a laser confocal Raman spectrometer. S700: Qualitative identification: Based on the characteristic Raman peak position of asiaticoside, combined with a pre-established OPLS-DA or LDA qualitative identification model, determine whether the sample contains asiaticoside. S800: Quantitative detection: Based on the intensity of the characteristic Raman peak of asiaticoside, the content of asiaticoside in the sample is calculated by substituting it into the pre-established quantitative calibration model.

7. An Au@AgNPs according to claim 6 The application of the PDMS thin-film SERS detection platform in the detection of asiaticoside in cosmetics is characterized by: In step S500, the volume fraction of the ethanol-water solution is 50%, the vortex mixing time is 10 min, the centrifugation speed is 8000 r / min, the centrifugation time is 10 min, and the pore size of the organic filter membrane is 0.22 μm.

8. An Au@AgNPs according to claim 6 The application of the PDMS thin-film SERS detection platform in the detection of asiaticoside in cosmetics is characterized by: The parameters of the laser confocal Raman spectrometer described in step S600 are set as follows: excitation wavelength 532 nm, laser power 4.25 mW, 100x objective lens, integration time 30 s, integration 3 times, and spectral scanning range 400 to 1800 cm⁻¹. -1 1cm resolution -1 .

9. An Au@AgNPs according to claim 6 The application of the PDMS thin-film SERS detection platform in the detection of asiaticoside in cosmetics is characterized by: The characteristic Raman peak position of asiaticoside in step S700 is 1320 cm⁻¹. -1 The characteristic peak at the specified position is used to establish an OPLS-DA model; the quantitative correction model described in step S800 is a linear equation, with asiaticoside at 1320 cm⁻¹ within a concentration range of 0.01 to 0.5 mg / mL. -1 Using the characteristic peak intensity at a given point as the response value and the logarithm of the asiaticoside concentration as the independent variable, a linear quantitative correction model was established.

10. An Au@AgNPs according to claim 6 The application of the PDMS thin-film SERS detection platform in the detection of asiaticoside in cosmetics is characterized by: It also includes methods for establishing qualitative identification models and quantitative correction models: a series of asiaticoside standard solutions were prepared, and SERS spectra were acquired using the Au@AgNPs-PDMS thin-film SERS detection platform. After baseline correction, Savitzky-Golay smoothing, and normalization preprocessing, a qualitative discrimination model was established using OPLS-DA and LDA; a linear quantitative correction model was established with the intensity of the characteristic Raman peak of asiaticoside as the response value and the logarithm of concentration as the independent variable.

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