Nano-plastic detection method based on Au-coated DMSN / Ag-coated G SERS composite substrate

Abstract

The invention relates to a nano-plastic detection method based on an Au (at) DMSN / Ag (at) G SERS (Surface Enhanced Raman Scattering) composite substrate, which comprises the following steps: preparing a composite material Au (at) DMSN / Ag (at) G obtained by compounding dendritic mesoporous silica filled with Au nanoparticles and graphene nanosheets deposited in situ by Ag nanoparticles, preparing an Au (at) DMSN / Ag (at) G solution, mixing the Au (at) DMSN / Ag (at) G solution with a polystyrene nanoparticle suspension, then adding KI as an aggregating agent, and carrying out in-situ deposition to obtain the Au (at) DMSN / Ag (at) G SERS composite substrate. The method comprises the following steps: fully mixing the solutions, standing until a sample forms a stable colloidal solution, dropwise adding the colloidal solution to a silicon wafer, drying, and carrying out SERS detection, and compared with the existing nano plastic analysis method, the method has the advantages of high sensitivity, interference resistance, good repeatability, strong quantitative analysis capability and the like.

Description

Technical Field

[0001] The present invention relates to the field of nanoplastics detection, and particularly to a method for detecting nanoplastics based on an Au@DMSN / Ag@G SERS composite substrate. Background Art

[0002] The widespread presence of microplastics (1 μm - 5 mm) and nanoplastics (<1000 nm) in the aquatic environment has attracted extensive global attention. Compared with microplastics, it is particularly important to note that the hazards of nanoplastics are more obvious, mainly due to their high specific surface area, which makes them prone to adsorb organic pollutants, heavy metals, pathogenic microorganisms, and plastic additives released during the degradation process. In order to anticipate and prevent the harm caused by nanoplastics to humans, it is necessary to monitor nanoplastics in the aquatic environment.

[0003] Currently, various complex techniques are used for the analysis and detection of micro / nanoplastics, such as pyrolysis-gas chromatography / mass spectrometry (Pyrolysis-GC / MS), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), transmission electron microscopy (TEM) observation, biosensor methods, and Raman spectroscopy. Although the above methods can quantitatively detect plastics in the environment, they also have drawbacks such as complex procedures, time-consuming, and destructive analysis. Biosensor methods are usually sensitive to pH values, which can make the detection results of samples unreliable under complex environmental conditions. Raman spectroscopy can accurately identify the fingerprint information of the molecular structure on the surface of nanoplastics. Unfortunately, classical Raman spectroscopy is limited by its limited spatial resolution and sample fluorescence interference.

[0004] Surface-enhanced Raman spectroscopy (SERS) is well-known for its high sensitivity. It can amplify the Raman signals of molecules within the local electric field range on a metal substrate at the nanoscale, which helps detect molecules at extremely low concentrations. However, due to the inherently low-scattering interfaces of various nanoplastics, the signals obtained from SERS detection of nanoplastics are generally considered weak. Therefore, applying SERS to nanoplastics detection remains challenging. Developing new SERS substrates to improve the detection efficiency is usually a laborious and time-consuming process, and it is still challenging to achieve the detection of ultra-low concentrations of nanoplastics in water bodies. Currently, the amplification of SERS signals comes from the enhancement of the local electromagnetic field of noble metal nanoparticles. Many research groups have successfully detected micro / nanoplastics using SERS substrates functionalized with noble metal nanoparticles. For example, Sang-Woo Joo et al. designed a method for preparing Au NSs@Ag@AAO SERS substrates by ultrasonic-induced self-assembly and achieved ultrasensitive detection of submicron PS plastics. Based on the former, Jing Yu et al. designed an AAO / MoS2 / Ag with a structure having MoS2 particles as a Raman internal standard coating and achieved the detection of NPs (<300 nm) and Hg 2+ . However, common substrates may have uneven hot spot distributions, resulting in a lack of reliability and consistency in SERS spectral signals. Wei Zhang et al. developed a ZnO nanorod array SERS substrate mimicking dragonfly wings modified with Ag NPs on polydimethylsiloxane. This substrate has advantages such as high sensitivity and signal reproducibility and achieved trace analysis of microplastics. The research work of these scholars has improved the detection sensitivity of nanoplastics, and the detection limits of PS NPs (polystyrene nanoparticles) are 50 μg / mL and 25 μg / mL respectively. To address the detection problem of ultra-low concentrations of nanoplastics (at 10 -9 -10 -4 g / mL) in the aquatic environment in real scenarios, it is necessary to develop new SERS substrates for nanoplastics detection to improve the detection sensitivity and accuracy of nanoplastics and to meet the detection requirements of nanoplastics in the aquatic environment as much as possible. Summary of the Invention

[0005] Aiming at the deficiencies of the above-mentioned existing technologies, the present invention provides a method for detecting nanoplastics based on an Au@DMSN / Ag@G SERS composite substrate.

[0006] The specific technical solution of the present invention is as follows: In the first aspect of the present invention, there is provided a method for detecting nanoplastics based on an Au@DMSN / Ag@G SERS composite substrate, including the following steps: S1 Preparation of Au@DMSN / Ag@G composite material composed of Au@DMSN dendritic mesoporous silica filled with Au nanoparticles and Ag@G graphene nanosheets in situ deposited with Ag nanoparticles as SERS composite substrate material. S2: Prepare Au@DMSN / Ag@G solution, then mix it with polystyrene nanoparticle suspension and add KI as aggregation agent. After the above solutions are fully mixed, let it stand and wait for the sample to form a stable colloidal solution. S3: Add the colloidal solution dropwise to the silicon wafer, dry it, and then perform SERS detection.

[0007] Graphene's inherent two-dimensional lattice structure gives it excellent optoelectronic properties, including high electron mobility under ambient conditions, which offers significant advantages in sensor, supercapacitor, and electrocatalytic applications. However, using graphene alone as a SERS substrate has certain limitations. Ag NPs combined with graphene can minimize these limitations and provide additional synergistic properties, namely, higher effective surface area, catalytic activity, conductivity, water solubility, and biocompatibility.

[0008] The surface of dendritic mesoporous silica (DMSN) exhibits excellent chemical durability and highly active areas for metal nanoparticle deposition. The uniform porous structure of DMSN serves as a template for the immobilization of metal nanoparticles, generating dense hotspots to enhance Raman signals. When combined with two-dimensional materials, the porous structure of the two-dimensional materials can effectively manipulate metal nanoparticles in sub-nanometer gaps, enabling highly sensitive SERS detection and photothermal therapy.

[0009] This application uses the composite material Au@DMSN / Ag@G SERS as a substrate for nanoplastic detection. This substrate overcomes the limitations of traditional two-dimensional substrates through the synergistic effect of gold / silver. In addition, due to the simultaneous use of two-dimensional and three-dimensional materials with high specific surface areas, the metal nanoparticles incorporated into its surface can exhibit excellent flexibility, and there is more contact space between the prepared SERS active substrate and the analyte, which helps to improve the SERS detection intensity and sensitivity, and realize the qualitative analysis of ultra-low concentration and wide-sized PS NPs in various environments.

[0010] Preferably, step S1 includes the following steps: S11 Preparation of DMSN-NH2; 1) Synthesis of dendritic mesoporous silica nanostructured DMSN with semi-compatible pore structure, Mix triethanolamine with deionized water at 70 - 90 °C with stirring, then add cetyltrimethylammonium bromide and sodium salicylate, and continue stirring for reaction. Subsequently, dropwise add tetraethyl orthosilicate into the above solution and stir for reaction at 75 - 85 °C. After the reaction is completed, centrifuge and wash. Then, wash the obtained precipitate with a mixed solution of HCl and ethanol to remove the residual organic template. Finally, vacuum dry to obtain dendritic mesoporous silica nanoparticles DMSN with a semi-compatible pore structure; preferably, triethanolamine:deionized water:cetyltrimethylammonium bromide:sodium salicylate:tetraethyl orthosilicate = 0.65 - 0.70 g:20 - 25 mL:0.35 - 0.40 g:0.16 - 0.17 g:3 - 5 mL. In the mixed solution of HCl and ethanol, by volume ratio, HCl:ethanol = 1:9, and the mass percentage concentration of HCl is 38%; the temperature for washing the residual organic template is 70 - 90 °C.

[0011] 2) Amino modification of DMSN First, disperse the dendritic mesoporous silica DMSN with a semi-compatible pore structure obtained in step S11 in ethanol, then add ammonia water, deionized water, and (3-aminopropyl)triethoxysilane under vigorous stirring, continue vigorous stirring, and finally wash the final product with ethanol and vacuum dry to obtain DMSN-NH2; preferably, DMSN:ethanol:ammonia water:deionized water:(3-aminopropyl)triethoxysilane = 90 - 100 mg:80 - 120 mL:2 - 3 mL:2 - 3 mL:0.5 - 2 mL; 3) Disperse the synthesized DMSN-NH2 in step 2) into ultrapure water, then add chloroauric acid solution under an ice-water bath condition and stir for reaction. After that, continue to add TSC solution under vigorous stirring conditions, then quickly add a newly prepared NaBH4 solution and continue the reaction. After the reaction is completed, centrifuge, wash, and dry to obtain Au@DMSN powder; preferably, the concentration of the chloroauric acid solution is 200 mg / mL, the concentration of the TSC solution is 1 w / v%, the concentration of the NaBH4 solution is 0.1 M, and by volume ratio, chloroauric acid:TSC:NaBH4 = 15 - 25:90 - 110:45 - 55.

[0012] S12 Prepare Ag@G Disperse graphene nanosheets G in deionized water, then heat up to a constant temperature of 80 - 85 °C; then add AgNO3 solution and keep stirring for reaction, then heat up to a constant temperature of 90 - 95 °C, and immediately add trisodium citrate solution for reaction to finally obtain graphene nanosheets Ag@G with in-situ deposited plasmonic Ag nanoparticles; preferably, by weight ratio, graphene nanosheets G:AgNO3 = 10:35 - 40.

[0013] S13 Au@DMSN / Ag@G Disperse the Au@DMSN and Ag@G obtained in steps S11 and S12 into deionized water, and after uniform compounding, the Au@DMSN / Ag@G composite material is obtained.

[0014] The dosages of different composite components in the substrate also affect each other. Preferably, in step S13, according to the mass ratio, the mass ratio of Au@DMSN:Ag@G is 1 - 4:4 - 1.

[0015] KI has a significant effect on the Raman activity of the substrate, and both too high and too low are not conducive to detection. Preferably, in the colloidal solution obtained in step S2, the KI concentration is 0.05 - 0.25 M.

[0016] A small amount of hot spot signals are generated at a low substrate dosage, and the SERS intensity is relatively low. However, when the substrate dosage is too large, it is possible that some PS NPs are covered by the SERS substrate, which inevitably leads to the loss of the SERS signals of some nanoplastics. Therefore, it is necessary to select an appropriate substrate solution concentration. Preferably, the concentration of the Au@DMSN / Ag@G solution is 0.15 - 1.5 mg / mL.

[0017] Preferably, the nanoplastics have a particle size of 200 - 500 nm.

[0018] Preferably, in step S3, the SERS detection uses 1000 cm -1 as the characteristic peak, with a relatively high intensity and no interfering peaks nearby.

[0019] Preferably, the SERS detection includes qualitative detection and / or quantitative detection. The quantitative detection draws a relationship curve between the characteristic peak intensity and the nanoplastics concentration according to the Raman spectral intensity of the characteristic peak to determine the nanoplastics concentration of the sample to be measured. In an embodiment of the present invention, the relationship curve is y = 527.20x + 2318.26, R 2 = 0.996. Wherein, y is the SERS intensity and x is the mass concentration of PS nanoplastics.

[0020] The beneficial effects of the present invention are: The present invention proposes a SERS detection method based on an Au@DMSN / Ag@G substrate. This detection platform overcomes the limitations of traditional two-dimensional substrates through the synergistic effect of gold / silver, and the two-component recognition ensures reliability in complex matrices. The detection method of the present invention can be used for ultrasensitive detection of nanoplastics (200 - 500 nm, sub-ppb level) in aquatic systems. In the size range of 200 - 500 nm, there is a good linear relationship between the concentration of PS NPs and the SERS intensity (R 2=0.996), and the enhancement factor reaches 3.67×10 4 , with a detection limit as low as 0.1 μg / mL. It can also successfully distinguish two-component nanoplastics. In addition, PS NPs show excellent stability at different SERS substrate detection sites and can cope with the interference of different actual environments for detection. The recovery rate of spiked detection in lake water is 91.18% - 109.27%, and the relative standard deviation (RSD) is 3.24%-11.66%, which realizes the quantitative analysis of wide-size nanoplastics for environmental diversity and solves the key gap in quantifying trace nanoplastics with heterogeneous size composition. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Flow chart of the detection method of the present invention; Figure 2 Wide-angle XRD diffraction patterns of DMSN, Au@DMSN, G, Ag@G, Au, and Ag; Figure 3 UV-visible absorption spectra of (a) DMSN, Au@DMSN, (b) G, Ag@G; Figure 4 (a) XPS spectra of Au@DMSN, Ag@G and Au@DMSN / Ag@G; (b) high-resolution XPS spectra of Ag 3d, (c) Au 4f and (d) N 1s; Figure 5 Transmission electron microscopy images of (af) Au@DMSN and (gl) Ag@G; Figure 6 Scanning electron microscopy images of (a, b) DMSN, (c) Au@DMSN / Ag@G; Figure 7 (a) FTIR spectra of DMSN and DMSN-NH2, (b) Zeta potential distribution of DMSN, DMSN-NH2 and Au@DMSN, (c) N2 adsorption-desorption isotherms and pore size distribution of DMSN and DMSN-NH2, (d) Thermogravimetric characterization of Au@DMSN, Ag@G and Au@DMSN / Ag@G; Figure 8 (a) Raman spectra of Au@DMSN / Ag@G and PS, (b) test results of PS NPs with different particle sizes; Figure 9 is the particle size distribution diagram of the test sample PS NPs; Figure 10(a) Raman spectra of 200 - 500 nm PS NPs (0.1 mg / mL) at different KI concentration dosages, (b) related SERS intensities at 1000 cm -1 in (a); Figure 11 (a) Raman spectra of 200 - 500 nm PS NPs (0.05 mg / mL) at different dosage ratios between precursor materials, (b) related SERS intensities at 1000 cm -1 in (a); Figure 12 (a) Raman spectra of 200 - 500 nm PS NPs (0.1 mg / mL) at different volume ratios of PS solution to SERS substrate dosages, (b) related SERS intensities at 1000 cm -1 in (a); Figure 13 (a) Raman spectra of 200 - 500 nm PS NPs (0.01 mg / mL) at different SERS concentration dosages, (b) related SERS intensities at 1000 cm -1 in (a); Figure 14 (a) SERS analysis of 200 - 500 nm PS NPs at different concentrations, (b) linear relationship between SERS intensities of 200 - 500 nm PS NPs at 1000 cm -1 ; Figure 15 (a) SERS intensities of 10 -2 mg / mL PS NPs in the presence of different interfering substances; (b) SERS spectra of binary components of PS and PMMA; (c) SERS spectra of PS NPs (10 -2 mg / mL) at 22 different random sites on the Au@DMSN / Ag@G substrate; (d) results of experimental reproducibility analysis; Figure 16 Locations of different sampling points for SERS testing of actual water samples: (a) Pearl River waters, (b) Dadonghai Tourist Area in Sanya City, (c) Suburban area of Ningyuan County, Yongzhou City; and (d) test chart of blank matrix of Pearl River water, (e) high - salinity seawater in Dadonghai Tourist Area, (f - g) test effect diagrams of spiked samples of well water and polluted water in the suburban area of Ningyuan County; Figure 17 (a) UV - visible absorption spectra of 200 - 500 nm PS NPs at different concentrations and (b) linear correlation relationship; Figure 18Statistical graph of the detection results of different substrates and different concentrations of PS NPs. DETAILED DESCRIPTION

[0022] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings and examples. Preferred embodiments of the present invention are provided below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure of the present invention.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in this specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0024] Unless otherwise specified, the reagents, materials, and equipment used in the examples of the present invention are all commercially available; and the experimental methods, unless otherwise specified, are all conventional experimental methods in the art.

[0025] Chemicals and Materials Triethanolamine (TEA, analytical grade), hexadecyltrimethylammonium bromide (CTAB, analytical grade), (3-aminopropyl)triethoxysilane (APTES, analytical grade), sodium salicylate (NaSal, analytical grade), tetraethyl orthosilicate (TEOS, analytical grade), chloroauric acid tetrahydrate (HAuCl4, analytical grade), silver nitrate (AgNO3, analytical grade), anhydrous ethanol (CH3CH2OH, analytical grade), sodium borohydride (NaBH4, analytical grade), ascorbic acid (analytical grade), trisodium citrate (TSC, analytical grade), graphene nanosheets (G, analytical grade), polystyrene nanoparticle suspension (PS NPs, 2.5%), calcium chloride (CaCl2, analytical grade), magnesium chloride (MgCl2, analytical grade), sodium chloride (NaCl, analytical grade), potassium chloride (KCl, analytical grade), glucose (analytical grade), PMMA (polymethyl methacrylate, 2.5%), sodium dodecylsulfonate (analytical grade), humic acid (fulvic acid ≥ 90%), C-phycocyanin (lyophilized powder), bovine serum albumin (dry powder), bisphenol A (analytical grade), lipopolysaccharide (analytical grade), tetracycline (analytical grade).

[0026] Instruments and equipment: The transmission electron microscope (TEM) images were obtained from FEI Talos F200X (USA); the XPS spectral images were obtained from AXIS SUPRA (Shimadzu, Japan); the field emission scanning electron microscope (SEM) images were obtained from ZEISS Ultra 55 (Carl Zeiss, Germany); the Fourier transform infrared spectroscopy diagrams were obtained from Spectrum Two (Germany); the ultraviolet-visible spectroscopy diagrams were obtained from UV2700 (Shimadzu, Japan); the X-ray powder diffractometer (XRD) was obtained from Ultima IV (Japan); the thermogravimetric analysis diagrams were obtained from TG-209F3 (NETZSCH, Germany); the BET specific surface area and pore size analysis diagrams were obtained from Quantachrome ASiQwin (Quantachrome, USA); the zeta potential data were obtained from Malvern Zetasizer Pro (Malvern, UK); the Raman spectroscopy analysis diagrams were obtained from Horiba LabRAM HR Evolution (HORIBA Jobin Yvon, France).

[0027] Preparation of the Au@DMSN / Ag@G substrate material in Example 1 Reference Figure 1 , the Au@DMSN / Ag@G composite material was prepared according to the following steps: S1 Preparation of Au@DMSN (1) Preparation of DMSN 0.68 g of TEA was added to a glass flask containing 25 mL of deionized water, placed in an oil bath at 80 °C and stirred for 30 minutes, then 0.38 g of CTAB and 0.168 g of NaSal were added, and after continuing to stir for 1 h, 4 mL of TEOS was uniformly added dropwise to the above mixed solution with a micropipette, and stirring was continued at 80 °C for 2 h. After the reaction was completed, the resulting product was collected by centrifugation at 9000 rpm for 10 min, and washed twice with ethanol and deionized water each to remove the residual reactants. Subsequently, the obtained precipitate was washed three times (24 h each time) with a mixed solution of HCl and ethanol (HCl:ethanol = 1:9 V / V) at 80 °C to remove the residual organic template, and finally vacuum dried at 50 °C for 12 h to obtain a white solid sample.

[0028] (2) -NH2 modification of DMSN First, 100 mg of DMSN was dispersed in 100 mL of ethanol and sonicated for 10 minutes, followed by continuous stirring for 15 min. Then, 2.5 mL of ammonia water, 2.5 mL of deionized water, and 1 mL of APTES were added to the above solution under vigorous stirring, and stirring was continued vigorously for 12 h. Finally, the final product was washed several times with ethanol and dried overnight at 50 °C in vacuo to obtain DMSN-NH2 powder.

[0029] (3)Preparation of Au@DMSN The synthesized DMSN-NH2 in S12 was dispersed into 20 mL of ultrapure water by sonication, and then 20 μL of 200 mg / mL chloroauric acid solution was added under an ice-water bath condition. After continuous stirring for 1 h, 100 μL of 1% TSC solution was added under vigorous stirring condition, and then 50 μL of freshly prepared 0.1 M NaBH4 solution was quickly added, and the reaction continued for 1 h. After the reaction was completed, the product was collected by centrifugation at 8000 rpm for 5 min, washed three times with ethanol, and dried overnight at 40 °C to obtain Au@DMSN powder.

[0030] S2 Preparation of Ag@G Weighed 10 mg of G (graphene nanosheets) and added it to a 50 mL glass flask containing 10 mL of deionized water, sonicated for 5 min, and then heated to a constant temperature of 85 °C; weighed 36 mg of AgNO3, dissolved it in 5 mL of water, and then added it to the above precursor solution and kept stirring. After reacting for 15 min, the temperature was raised to a constant 90 °C, and then 4 mL of 1% trisodium citrate solution was added, and the reaction was kept for 40 min. After the reaction was completed, it was washed with ethanol and water, dispersed in deionized water, and stored for standby under low-temperature conditions.

[0031] S3 Au@DMSN / Ag@G Weighed appropriate amounts of Au@DMSN and Ag@G respectively, dispersed them in deionized water, and magnetically stirred for 30 min. After the materials were uniformly compounded, they were centrifuged and precipitated. Finally, the prepared Au@DMSN / Ag@G material was redissolved in deionized water to obtain the Au@DMSN / Ag@G substrate solution.

[0032] To prove the successful synthesis of the materials in the above steps, the following characterization tests were carried out: 1. XRD analysis XRD is a commonly used characterization method to verify the immobilization and crystallinity of nanoparticles. Therefore, XRD analyses were performed on DMSN, Au@DMSN, G, and Ag@G respectively, and their wide-angle XRD diffraction patterns are as Figure 2As shown, the broad peak at 22.9° is attributed to amorphous silica. The five diffraction peaks of Au@DMSN at 2θ = 38.1°, 44.4°, 64.6°, 77.5°, and 81.8° correspond to the (111), (200), (220), (311), and (222) lattice planes of Au (JCPDS Card No. 04-0784); this indicates that Au nanoparticles have been successfully grown on the DMSN surface. Similarly, the 2θ = 37.8°, 44.0°, 64.2°, 77.2°, and 81.3° of Ag@G correspond to the (111), (200), (220), (311), and (222) lattice planes of Ag (JCPDS Card No. 87-0597), confirming the successful loading of Ag nanoparticles. XRD results confirmed the successful complexation of noble metal nanoparticles on the surfaces of mesoporous silica (DMSN) and graphene nanosheets (G).

[0033] 2. UV-visible absorption spectrum Due to the local plasma resonance effect of the noble metal, the noble metal particles have obvious UV-visible absorption peaks, which further proves the successful loading of the noble metal nanoparticles. The UV-visible absorption spectra of Au@DMSN and Ag@G were tested, as shown in Figure 3 As shown in (a) and (b), the absorption peaks of Au NPs and Ag NPs are at 536 nm and 446 nm, respectively. Based on Mie light scattering theory, the particle size of Ag NPs was calculated to be 60.3 nm, which is consistent with the results of SEM characterization.

[0034] 3. XPS analysis XPS was used to confirm the surface composition and chemical state of the SERS substrate, such as Figure 4 As shown, the successful loading of Au NPs and Ag NPs and the successful synthesis of binary material composites were further demonstrated. Figure 4 (a) shows the presence of characteristic elements C, Si, N, O, and Au in the Au@DMSN energy spectrum, and C and Ag in the Ag@G energy spectrum, demonstrating the successful loading of Au NPs onto the DMSN surface and the successful in situ generation of Ag NPs onto the G surface. When Au@DMSN and Ag@G are composited, the significantly increased carbon content reduces the proportion of other elements to a certain extent, making the characteristics of these characteristic elements significantly reduced and difficult to observe. Figure 4 b shows that the Ag 3d spectrum of Ag@G presents two peaks at 368.85 and 374.85 eV, with a peak interval of 6.0 eV. These peaks are the Ag 3d 5 / 2 and Ag 3d 3 / 2The peaks at 374.02 and 368.02 eV, compared to the standard spectral peaks of pure Ag (374.02 and 368.02 eV), indicate an increase in the binding energy of AgNPs. Graphene, with its strong electronic interactions, facilitates SERS detection. Furthermore, the absence of the AgO peak in Figure 4b indicates that AgNPs have been successfully loaded onto the surface of the graphene nanosheets (G). Figure 4 c shows that Au@DMSN has two peaks at 84.56 eV and 88.23 eV with a peak separation of 3.67 eV. These peaks are consistent with the Au 4f 7 / 2 and Au 4f 5 / 2 In order to fully explore the advantages of Au@DMSN in surface enhanced Raman scattering (SERS) research, the trend of nitrogen (N) binding energy changes of gold nanoparticles (Au NPs) before and after DMSN-NH2 modification was analyzed in detail. Figure 4 As shown in Figure d, during the modification process, the formation of -NH- and N-Au bonds is consistent with references, while the -NH2 content decreases. This phenomenon strongly confirms that the Au NPs have been successfully in situ loaded onto the pore surface of the DMSN. Further investigation shows that the binding energy of N1S increases by 0.74 eV, indicating slight electron transfer between the Au NPs and the DMSN. In addition, a certain amount of low-density electron cloud is formed at the contact interface, which is highly beneficial for the preparation of highly sensitive SERS substrates.

[0035] TEM analysis TEM images ( Figure 5 Figures af) show that DMSN-NH2 has a distinct dendritic structure with a diameter of about 150 nm. The Au NPs of Au@DMSN are loaded on the DMSN surface in a semi-compatible state, successfully capturing the Au NPs. The EDS elemental map shows that Si, C, and Au elements are evenly distributed on the Au@DMSN matrix, which further proves the successful loading of Au nanoparticles. Figure 5gl also shows that Ag NPs are successfully deposited on the G surface. The average particle size of Ag NPs is about 60 nm, which is consistent with the particle size obtained by UV-visible absorption spectroscopy. It can be seen from the dotted line of the lattice diagram that the lattice stripe distribution spacing of Au NPs and AgNPs is about 0.23 nm, which is consistent with the lattice constant of the gold and silver (111) crystal planes in the face-centered cubic lattice structure. In addition, EDS elemental mapping showed that Au elements were successfully distributed around the mesopores of DMSN, and Ag elements were successfully distributed on the graphene nanosheets, further proving the successful loading of Au nanoparticles and Ag nanoparticles.

[0036] SEM analysis SEM images (Figure 6 a, b) show that the synthesized DMSN has obvious central radial channels and wrinkled morphology, indicating that the prepared DMSN has a semi-compatible loading space for metallic Au NPs. Figure 6 c, d show that Au@DMSN can be successfully dispersed onto the surface of Ag@G with high-density material rows, which provides sufficient 3D space for the reinforcement of nanoplastics and provides ordered filling gaps.

[0037] Infrared analysis shows that the preparation method of the embodiment of the present invention uses amino groups as adsorption anchoring groups of gold nanoparticles to achieve the purpose of semi-compatible loading of Au NPs with the surface pores of DMSN. Figure 7 a shows the FTIR characteristic spectra of DMSN before and after amino modification. It can be found that the weak symmetric stretching vibration of CH is at 2850-2950 cm -1 This indicates that APTES has been successfully modified. NH at 1546 cm -1 The vibration at the position further proves the successful grafting of amino groups.

[0038] Figure 7 As shown in Figure b, the zeta potential changes of DMSN, DMSN-NH2, and Au@DMSN demonstrate that the unmodified DMSN surface is negatively charged and rich in Si-OH groups, with a potential value of -37.88±0.8 mV. After amino modification, the DMSN surface is heavily modified with -NH2 groups, resulting in a positive potential change of 48.0±2.0 mV, consistent with our infrared measurements. When Au NPs are in situ loaded onto the noble metal surface, a small fraction of the -NH2 sites are occupied, slightly lowering the material's potential to 45.1 mV±1.6 mV. These highly positive potential values represent the excellent stability of the synthesized nanoparticles, while the significant zeta potential changes indicate successful amino modification and noble metal nanoparticle loading. These results, combined with XPS measurements, confirm the successful synthesis of the two precursor materials. Bamauer-Enunett-Teller (BET) analysis of DMSN reveals a type IV isotherm (Figure 7c), indicating the formation of a medium-sized mesoporous structure. In the Barrett-Joyner-Halenda (BJH) system, the distribution of the two peaks of DMSN illustrates the hierarchical pore structure of DMSN, with pore diameters ranging from 10 to 33 nm and an average pore diameter of 13.38 nm, proving that the synthesized DMSN has a medium-sized mesoporous structure. The successful grafting of amino groups increases the total specific surface area of DMSN from 454.67 m 2 / g decreased to 227.69 m 2 / g, the total pore volume is from 1.54 cm 3 / g reduced to 0.937 cm 3 / g, indicating that APTES successfully coated DMSN. This unique pore structure provides sufficient compatible space for loading noble metal nanoparticles.

[0039] 7. Thermogravimetric analysis As Figure 7 d shows the thermogravimetric characterization of Au@DMSN, Ag@G, and Au@DMSN / Ag@G. It can be seen from the figure that the thermogravimetric curves of Ag@G and Au@DMSN / Ag@G are roughly similar. It can be seen that Au@DMSN has a certain heat resistance stability due to its carrier being a polymer C and Si polymer, resulting in a carbonization process from the outer surface to the inside. When the temperature rises to 180 °C, G begins to decompose thermally, generating CO and CO2. Analyzing the mass fraction of the residue can conclude the successful composite of Au@DMSN and Ag@GNS.

[0040] Example 2 Detection method of PS NPs This example provides a method for detecting nanoplastics based on the Au@DMSN / Ag@G SERS composite substrate, including the following steps: S1 Prepare the Au@DMSN / Ag@G SERS composite substrate solution using the preparation method of Example 1. S2 Mix the prepared Au@DMSN / Ag@G composite substrate solution with the PS NPs solution, then add KI as an aggregating agent. After fully mixing the above solution, let it stand for 1 h to wait for the sample to form a stable colloidal solution.

[0041] S3 Use a glass micropipette to drop the mixed solution (20 μL) onto a 5×5 mm silicon wafer and dry it in an oven at 50 °C for 1 hour. Perform SERS detection on the dried sample.

[0042] Normal Raman and SERS spectra are obtained through a confocal laser microscope Raman spectrometer (Horiba LabRAM HR Evolution) and a 564 nm (3.5%) laser. During the Raman spectrum acquisition process, select a 50x objective lens, and the acquisition wavelength range is 400 - 1700 cm -1 There are 3 accumulations in a 5 s acquisition time.

[0043] Among them, the test concentration of the PS NPs nanoparticle suspension is obtained by diluting the standard PS NPs solution.

[0044] Example 3 Determination of characteristic peaks Raman scattering test characterization was performed on PS NPs with a particle size distribution range of 200 - 500 nm. As Figure 8As shown in a, the two most prominent characteristic peaks are located at 1000 cm -1 and 1030 cm -1 , corresponding to the breathing vibration peak of the benzene ring and the in-plane deformation of C-H respectively. There is a low peak at 1607 cm -1 , attributed to the skeletal stretching vibration of the benzene ring. Since the peak intensity at 1000 cm -1 is the strongest characteristic peak, the concentration of PS NPs is reflected by comparing the intensity of this peak subsequently.

[0045] In addition, it can be seen that for all substrates without signals near 1000 cm -1 and 1030 cm -1 , the interference of the SERS substrate on the detection of PS NPs can be excluded.

[0046] Secondly, as shown in Figure 8 b, for PS NPs with the same mass concentration, the SERS composite substrate can also detect PS NPs with particle sizes of 50 - 100 nm and 20 nm at a mass concentration of 10 -3 mg / mL. In summary, the SERS substrates prepared by the present invention can all detect PS NPs with particle sizes of 50 - 100 nm and 20 nm.

[0047] In the actual environment, plastics have the characteristic of differential particle size distribution. The research on PS NPs with a wide range of distributions is more innovative and representative. Here, PS NPs samples with a wide particle size range distribution are used as the main research object, and dynamic light scattering (DLS) experiments ( Figure 9 ) are carried out first, which proves that the particle size distribution range of PS NPs is mainly in 200 - 500 nm. In addition, due to its small nano size, it can enter the hot spot gap of the SERS composite material for attractive deposition between plastics. On the other hand, since the ordinary Raman characterization signals of the 50 - 100 nm and 20 nm PS suspensions are smaller than those of the 200 - 500 nm PS suspension, 200 - 500 nm PS with more SERS signal advantages is selected for subsequent experiments.

[0048] Example 4 Influence of the dosage of 4KI as a coagulant on the detection.

[0049] Taking the 200 - 500 nm PS suspension with a concentration of 0.1 mg / mL as a probe, V Au@DMSN / Ag@G :V PS NPs is fixed at 1:1, and the rest of the conditions are the same. The KI concentration in the colloidal solution is reduced from 0.25 mol / L to 0.10 mol / L, and SERS tests are carried out.

[0050] The results are asFigure 10 As shown in a and b, the SERS intensity at 1000 cm -1 The SERS intensity at 1000 cm increases from 816 to 1871 as the KI concentration decreases from 0.25 mol / L to 0.10 mol / L. However, when the KI concentration exceeds 0.10 mol / L, a further increase in concentration results in a decrease in the SERS intensity. This is because an excessive amount of KI will cover the surface layer due to the force during the drying process, thus hindering the contact distance between the nanoplastics and the SERS substrate, thereby affecting the Raman signal. Therefore, the optimal KI concentration is 0.10 mol / L for subsequent SERS analysis.

[0051] Example 5 Effect of the ratio of Au@DMSN to Ag@G in the substrate on detection.

[0052] Using 200 - 500 nm PS NPs (0.05 mg / mL) as the performance probe, in step S3 respectively, the mass ratio of m Au@DMSN to m Ag@G is 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, and the other conditions are the same, and SERS tests are carried out.

[0053] The results are as shown in Figure 11 a and b, the SERS intensity at 1000 cm -1 The SERS intensity at 1000 cm increases sharply from 529 when the ratio is 1:4 to 1581 when the ratio is 2:1 as the ratio of m Au@DMSN :m Ag@G increases. However, a further increase in the volume ratio results in a decrease in intensity. Therefore, the optimal response is shown at a ratio of 2:1. This may be attributed to the fact that as the amount of Au@DMSN increases, it compensates for the deficiency of Raman hotspots of Ag@G in three-dimensional space, but subsequently, due to the excessive amount of Au@DMSN, it is speculated that it hinders the contact between PS NPs and the SERS composite substrate.

[0054] Example 6 Effect of the ratio of the amount of substrate Au@DMSN / Ag@G solution to the amount of PS NPs on the detection results.

[0055] 6.1 Using 200 - 500 nm PS NPs (0.1 mg / mL) as the performance probe, adjust the ratio of V Au@DMSN / Ag@G :V PS NPs to 1:4, 1:3, 1:2, 4:4, 2:1, 3:1, and 4:1 respectively, and carry out SERS tests.

[0056] The test results are as shown in Figure 12 a and b, the SERS intensity at 1000 cm -1The SERS intensity at [specific location] increases as the volume ratio of the substrate to the nanoplastics solution increases. The signal intensity collected sharply increases from 984 at a ratio of 1:4 to 1916 at 4:4. However, a further increase in the volume ratio leads to a decrease in intensity. Therefore, the optimal response is shown at a ratio of 4:4. This is attributed to the generation of a small number of hot spot signals with a low substrate dosage, resulting in a relatively low SERS intensity. However, when the substrate volume is too large, it is possible that some PS NPs are covered by the SERS substrate, which inevitably leads to the loss of the SERS signal of some nanoplastics. Therefore, the experiments in the following are carried out at a volume ratio of 4:4.

[0057] 6.2 Cross Experiment Using 200 - 500 nm PS NPs with a concentration of 0.01 mg / mL as the probe, Raman detection was carried out using substrate solutions with concentrations of 1.5 mg / mL, 1.25 mg / mL, 0.75 mg / mL, 0.3 mg / mL, and 0.15 mg / mL.

[0058] The test results are as Figure 13 As can be seen from a, b, the SERS intensity at 1000 cm -1 increases as the substrate concentration increases, sharply increasing from 161 at 0.15 mg / mL to 1229 at 1.125 mg / mL. However, a further increase in the mass concentration leads to a decrease in intensity. Therefore, the optimal response is shown at a ratio of 1.125 mg / mL.

[0059] The above results correspond to the results of 6.1. Therefore, a SERS substrate concentration of 1.125 mg / mL was selected for the experiments in the following.

[0060] Example 7 Quantitative SERS Detection and Evaluation of PS NPs Using the optimal conditions determined in Examples 4 - 6, different standard concentrations of PS NPs were detected. Specifically: In the substrate synthesis, in step (4) of S1, the volume of the Au NPs solution is 11 mL, m Au@DMSN :m Ag@G = 2:1, V Au@DMSN / Ag@G :V PS NPs = 4:4, V Au@DMSN / Ag@G concentration 1.125 mg / mL; The KI concentration in the colloidal solution is 0.10 mol / L; PS NPs with different concentrations in a wide range of particle size distributions (200 - 500 nm) were tested. Select 1000 cm -1The Raman peaks obtained were used as the characteristic peaks of PS for quantitative analysis. According to the Raman spectral intensity of the characteristic peaks, a relationship curve between the characteristic peak intensity I and the logarithm of the PS concentration (lgC) was plotted to establish a quantitative analysis method, as shown in Figure 14 a and b.

[0061] According to Figure 14 a and b, as the concentration of PS NPs increased, the SERS intensity increased significantly, and its detection limit was 10 − 4 mg / mL. Further, according to the Raman spectral intensity of the characteristic peaks, a relationship curve between the characteristic peak intensity I and the logarithm of the PS concentration (lgC) was plotted. The linear concentration range was within 10 −4 -10 −1 mg / mL. At 1000 cm -1 , the SERS intensity had a good linear relationship with the logarithm of the mass concentration. The linear fitting equation was y = 527.20x + 2318.26, and R 2 = 0.996.

[0062] Meanwhile, the enhancement factor (EF) is one of the important parameters for evaluating the characteristics of SERS substrates. The enhancement of the detection method of the present invention was calculated as follows.

[0063]

[0064] Wherein, I SERS and I blank represent the normal Raman and SERS signals of the analyte solution at the characteristic spectrum. C SERS and C blank represent the concentrations of the target solution used in SERS detection and normal Raman detection. Based on Figure 8 the normal 10 mg / mL PS Raman signal in a and Figure 14 the SERS signal in, the calculated result of EF was 3.67×10 4 . It was 12.6 times higher than the recently reported Ag composite filter membrane substrate [1] .

[0065] Furthermore, Table 1 shows the performance comparison between the detection method of this application and related SERS analysis PS NPs sensors in the field, to further evaluate the detection method of this application. On the premise of quantitative detection, the detection limit of the detection method of this application based on the prepared Au@DMSN / Ag@G substrate is better than the related work in the field recently.

[0066] Table 1. Performance comparison of analyzing PS NPs based on the SERS method

[0067] Analysis of the Uniformity, Anti-Interference Ability, and Selectivity of the Detection Method in Example 8 To verify the reliability, anti-interference ability, and selectivity of this method in application and improve the credibility of experimental data, we evaluated the anti-interference ability, uniformity, and selectivity of this method using a PS standard solution.

[0068] (1) Anti-interference ability: Using the representative interfering substances that may exist in the actual aquatic environment, with NaCl, KCl, CaCl2, MgCl2, glucose, sodium dodecyl sulfate, humic acid, C-phycocyanin, bovine serum albumin, bisphenol A, and tetracycline as the interference test substances, we simulated the interference environment of a single series of substances in the aquatic environment and collected and detected the signals of PS NPs (200 - 500 nm, 10 −2 mg / mL).

[0069] The results are as Figure 15 shown in 2+ a, indicating that in the interference environment of a single series of substances (0.8 mg / mL Ca + , 58 mg / mL Na + , 1.1 mg / mL Mg2 + , 1.6 mg / mL K −2 , 2 mg / mL glucose, 1 μg / mL sodium dodecyl sulfate, 5 μg / mL humic acid, 1 μg / mL C-phycocyanin, 1 μg / mL bovine serum albumin, 1 μg / mL bisphenol A, 1 μg / mL tetracycline), the SERS intensity of PS NPs is less affected. This shows that the detection method based on the Au@DMSN / Ag@G substrate of the present invention can still effectively identify and detect PS in the presence of interfering substances. (2) Selectivity: PS NPs (200 - 500 nm, 10 1 mg / mL) were mixed with PMMA NPs (300 nm, 1 mg / mL) for SERS detection.

[0071] As Figure 15 shown in −1 b, the characteristic spectra of PS NPs (1000 cm- -1 ) and PMMA NPs (596, 816 cm -1 ) were detected respectively when measuring PS NPs and PMMA NPs. When they were mixed together, these Raman characteristic peaks still existed without obvious peak shifts. The results show that the detection method of the present invention can distinguish the content in the mixture of nanoplastics characteristic peaks and can be used to detect different types of nanoplastics in complex environments.

[0072] (3) Stability: 0.01 mg / mL 200 - 500 nm PS NPs were selected as the research object, and SERS spectra were collected at 22 randomly selected positions on the silicon wafer.

[0073] The results are shown as follows Figure 15 c. There were no significant differences in the SERS spectra at different detection sites. Further analysis of the response intensity of the characteristic peak at 1000 cm -1 revealed that their response intensities were between 1116 and 1327. The average intensity was 1220, and the relative standard deviation (RSD) was 5.48%. Under the same experimental conditions, repeatability tests were further carried out to improve the reliability of the experimental results. As shown in Figure 15d, the experiment was carried out in parallel with five groups of experiments, and three points were randomly selected on each final experimental sample obtained in each group for Raman spectroscopy analysis. Raman spectral data of each point were collected, and the average relative standard deviation (RSD) of the characteristic peak intensities at each point was approximately 3.49 ± 1.21%. The results indicated that the prepared SERS substrate had good stability.

[0074] Evaluation of the practicability and accuracy of the detection method in Example 9 PS NPs with different concentrations (200 - 500 nm) were added to lake water. The lake water was taken from the Pearl River Lake in summer. After the samples were left standing overnight, the supernatant was taken and used directly without further processing.

[0075] (1) Practicability: A standard addition recovery experiment was carried out using the Pearl River water as the matrix.

[0076] First, a certain volume of Pearl River water was left standing overnight, and then the supernatant was taken for use. A certain volume of PS solution was measured and prepared into 100 μg / mL, 10 μg / mL, 2 μg / mL, 1 μg / mL, 0.5 μg / mL, and then added to Au@DMSN / Ag@G in equal volumes. Then, 20 μL of 0.1M KI was added and shaken, and then left standing for incubation for 1 h. After the incubation ended, 20 μL was taken and dropped onto the silicon wafer, dried at 50 °C for 30 min, and then SERS detection was carried out.

[0077] The Pearl River water was taken in summer, and its geographical location is shown in Figure 16a. After the samples were left standing overnight, the supernatant was taken and used directly without further treatment. As shown in Figure 16d, no SERS signal response was detected in the initial water samples by the above detection method. Therefore, a standard addition recovery experiment was carried out on PS NPs, and the results are shown in Table 2. The recovery rates of PS NPs were from 91.18% to 109.27%, and the RSD (n = 3) ranged from 3.24% to 11.66%.

[0078] In addition, simple simulated spiking tests were also carried out on the nearshore seawater in the Dadonghai Tourist Area of Sanya City, the groundwater in the suburbs of Ningyuan County, Yongzhou City, and the water samples in the nearby polluted ditches. The sampling locations are shown in Figures 16b and c. Further analysis showed that the characteristic signal of PS NPs was not detected at 1000 cm -1 . Therefore, PS NPs with a concentration of 0.5 μg / mL were simulated and added to the above actual water samples. The results are shown in Figures 16e - g, and all the added nanoplastics could be detected by the SERS substrate.

[0079] Table 2. Results of the spiking recovery experiment for actual environmental water samples

[0080] The above results illustrate that the SERS substrate prepared in the embodiments of the present invention overcomes the problem of the high detection limit of SERS technology for nanoplastics in salt water and polluted environments, and also proves that the prepared SERS substrate has excellent environmental adaptability.

[0081] (2) Accuracy: Comparative evaluation was carried out using ultraviolet - visible spectrophotometry.

[0082] First, a linear equation of the absorbance intensity and concentration of PS NPs with a particle size of 200 - 500 nm was established. Based on this, a spiking test of lake water was carried out using the ultraviolet - visible spectrophotometric method and compared with the proposed SERS method. The results are as Figure 17 shown in a, b. The RSD value of the ultraviolet - visible spectrophotometer is very small, but the fluctuation range of the recovery rate is very large, from 49.83% to 134.95%. Obviously, the ultraviolet - visible spectrophotometric method cannot be used to test the PS concentration in real water samples.

[0083] These results confirm the superiority and feasibility of the detection method of the present invention in the detection of real aquatic environments.

[0084] Example 10 Comparison of the detection effects of different substrates Referring to the steps in Example 1, DMSN, Ag@G, and Au@DMSN were respectively prepared, and graphene G was also prepared.

[0085] Meanwhile, Au NPs were synthesized by the citrate reduction method. Specifically, 24 μL of an aqueous solution of chloroauric acid tetrahydrate with a concentration of 200 g / L was added to 50 mL of distilled water. The solution was placed in a water bath at 120 °C and heated to boiling under stirring conditions, and then 0.5 mL of a 1% sodium citrate solution was quickly added. After continuous reaction for 30 min, the heating was stopped when the solution color turned into a stable wine - red color, and it was cooled to room temperature for standby.

[0086] And synthesize Ag NPs. Specifically, dissolve 0.3 g of polyvinylpyrrolidone (PVP) in 17 mL of ethylene glycol at room temperature, then place it in an oil bath at 160 °C for heating and stirring. Subsequently, dissolve 110 mg of AgNO3 in 3 mL of ethylene glycol, slowly add it dropwise to the PVP solution, and continue heating for 30 min. After the reaction, centrifuge at a frequency of 9000 r / min for 10 min. The obtained product, Ag nanoparticles (Ag NPs), is washed twice with ethanol and finally redispersed in 20 mL of ethanol.

[0087] Use the above 6 samples and the Au@DMSN / Ag@G synthesized in Example 1 as substrates for detection.

[0088] Specifically, based on the optimal conditions determined in Examples 4 - 6, detect PS NPs with different standard concentrations. In the synthesis of the Au@DMSN / Ag@G substrate, in step S1(4), the volume of the Au NPs solution is 11 mL, mAu@DMSN:mAg@G = 2:1, VAu@DMSN / Ag@G:VPS NPs = 4:4, the concentration of VAu@DMSN / Ag@G is 1.125 mg / mL; The concentration of KI in the colloidal solution is 0.10 mol / L.

[0089] Use PS NPs with concentrations of 10 μg / mL and 1 μg / mL as probes respectively to conduct SERS tests on each sample. The results are as Figure 18 shown. It can be seen that: Due to their non-plasmonic structures, DMSN and graphene nanosheets (G) cannot enhance the SERS signal, and PS NPs cannot be detected; As plasmonic materials, Au NPs and Ag NPs can adhere to the surface of PS NPs through hydrophobic / electrostatic interactions and generate SERS enhancement. However, limited by the weak signal characteristics of PS NPs themselves, only weak characteristic peaks can be detected at a concentration of 10 μg / mL; Thanks to the dendritic mesoporous structure and high specific surface area of DMSN, Au@DMSN forms a three-dimensional satellite-like structure with abundant plasmonic nanogaps, successfully enhancing the signal in multiple dimensions and detecting 1 μg / mL of PS NPs; Although Ag@G has a stronger signal than Ag NPs due to the high specific surface area two-dimensional plane and excellent conductivity of graphene nanosheets, it still cannot detect 1 μg / mL of PS NPs due to the lack of three-dimensional spatial hot spot distribution.

[0090] This demonstrates that the Au@DMSN / Ag@G composite prepared in this embodiment of the present invention achieves a unique three-dimensional "hotspot enclosure" effect: PS NPs form high-intensity hotspot contacts with Ag@G at the bottom, while their surface achieves multi-point electromagnetic field coupling through the three-dimensional porous network constructed by Au@DMSN. The monodispersity of Au@DMSN creates a dynamic pore structure with subnanometer precision, generating a graded confinement effect, encapsulating the PS NPs in a physical potential well formed by the oscillating field of the noble metal plasmon. Its layered topology effectively suppresses nanoplastic aggregation. From a materials perspective, the monodispersity of Au@DMSN overcomes signal fluctuations caused by the wide size distribution of PS NPs (20-500 nm) and provides a clean Raman background. From an interface engineering perspective, the introduction of Ag@G realizes a "gravity compensation mechanism"—when PS NPs settle due to gravity, the bottom Ag@G provides high-density hotspot contacts, while the upper Au@DMSN layer extends the hotspots vertically to form a three-dimensional enhanced network. This synergistic effect enables the composite substrate to clearly detect 1 μg / mL PS NPs.

[0091] In summary, it can be seen that the present invention has established a SERS detection method for quantitative analysis of low-concentration nanoplastics in aquatic environments. By rationally designing a two-dimensional planar substrate with excellent conductive properties and simultaneously loading plasma Ag NPs; at the same time, based on the Stober mechanism and sol-gel strategy, DMSN with a semi-compatible pore structure with Au NPs was synthesized. The Au@DMSN / Ag@G composite material was successfully prepared as a SERS substrate through electrostatic attraction. Combined with the optimization of detection conditions, it is possible to detect PS NPs in a range of sizes from 200 to 500 nm, and a linear relationship between the concentration and intensity of the Raman characteristic peak (R 2 >0.996). Compared with the current nanoplastic analysis methods, this method has high sensitivity (the detection limit of 200-500 nm PS nanoplastics is as low as 10 -4 The proposed method has the advantages of high sensitivity, high sensitivity, high reproducibility, and strong quantitative analysis capabilities. Furthermore, the proposed method achieved good recoveries (91.18% - 109.27%) in lake water labeling experiments.

[0092] References: [1] Wu J, Li Y, Liu X, et al. Integration of bifunctional silverdendrite membranes with surface-enhanced Raman scattering for sensitivedetection of polystyrene microplastics in aquatic environments [J]. J HazardMater, 2024, 480: 136394. [2] Zhou X-X, Liu R, Hao L-T, et al. Identification of polystyrenenanoplastics using surface enhanced Raman spectroscopy [J]. Talanta, 2021,221: 121552. [3] Hu R, Zhang K, Wang W, et al. Quantitative and sensitive analysisof polystyrene nanoplastics down to 50 nm by surface-enhanced Ramanspectroscopy in water [J]. J Hazard Mater, 2022, 429: 128388. [4] Mikac L, Rigó I, Himics L, et al. Surface-enhanced Ramanspectroscopy for the detection of microplastics [J]. Appl Surf Sci, 2023,608. [5] Zhou X X, Liu R, Hao L T, et al. Identification of polystyrenenanoplastics using surface enhanced Raman spectroscopy [J]. Talanta, 2021,221: 121552. [6] Lê Q T, LY N H, Kim M-K, et al. Nanostructured Raman substratesfor the sensitive detection of submicrometer-sized plastic pollutants inwater [J]. Journal of Hazardous Materials, 2021, 402. [7] Zhu Z, Han K, Feng Y, et al. Biomimetic Ag / ZnO@PDMS HybridNanorod Array-Mediated Photo-induced Enhanced Raman Spectroscopy Sensor forQuantitative and Visualized Analysis of Microplastics [J]. ACS Appl MaterInterfaces, 2023, 15(30): 36988-98. [8] Li Z, Han K, Zhang A, et al. Honeycomb-like AgNPs@TiO2array SERSsensor for the quantification of micro / nanoplastics in the environmentalwater samples[J]. Talanta, 2024, 266(Pt 2): 125070. [9] Jiang Y, Wang X, Zhao G, et al. Silver nanostars arrayed on GO / MWCNT composite membranes for enrichment and SERS detection of polystyrenenanoplastics in water [J]. Water Res, 2024, 255: 121444. The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of this invention patent shall be subject to the appended claims.

Claims

1. A method for detecting nanoplastics based on an Au@DMSN / Ag@G SERS composite substrate, characterized in that, The steps include: S1 Preparation of Au@DMSN / Ag@G composite material composed of Au@DMSN dendritic mesoporous silica filled with Au nanoparticles and Ag@G graphene nanosheets in situ deposited with Ag nanoparticles as SERS composite substrate material. S2: Prepare Au@DMSN / Ag@G solution, then mix it with polystyrene nanoparticle suspension and add KI as aggregating agent. After the above solutions are fully mixed, let them stand and wait for the sample to form a stable colloidal solution. S3: Add the colloidal solution dropwise to the silicon wafer, dry it, and then perform SERS detection.

2. The nano-plastic detection method according to claim 1, characterized in that, The step S1 includes the following steps: S11 Preparation of DMSN-NH2; 1) Synthesis of dendritic mesoporous silica DMSN with semi-compatible pore structure, Triethanolamine and deionized water are mixed and stirred at 70-90°C, and then hexadecyltrimethylammonium bromide and sodium salicylate are added, and the reaction is continued with stirring. Then, ethyl orthosilicate is added dropwise to the above solution, and the reaction is stirred at 75-85°C. After the reaction is completed, the mixture is centrifuged and washed. Subsequently, the obtained precipitate is washed with a mixed solution of HCl and ethanol to remove the residual organic template, and finally dried in vacuum to obtain dendritic mesoporous silica DMSN with a semi-compatible pore structure; 2) Amino modification of DMSN, First, the dendritic mesoporous silica DMSN with a semi-compatible pore structure obtained in step S11 is dispersed in ethanol, and then ammonia water, deionized water, and (3-aminopropyl) triethoxysilane are added under vigorous stirring, and vigorous stirring is continued. Finally, the final product is washed with ethanol and vacuum dried to obtain DMSN-NH2; 3) The DMSN-NH2 synthesized in step 2) is dispersed in ultrapure water, and then the chloroauric acid solution is added in an ice-water bath and stirred for reaction. Then, the TSC solution is added under vigorous stirring, and then the freshly prepared NaBH4 solution is quickly added and the reaction is continued. After the reaction is completed, the Au@DMSN powder is obtained by centrifugation, washing, and drying. S12 Preparation of Ag@G; Graphene nanosheets G are dispersed in deionized water and then heated to a constant temperature of 80-85°C. AgNO3 solution is then added and stirred for reaction. The temperature is then raised to a constant temperature of 90-95°C, followed by addition of trisodium citrate solution to react, ultimately obtaining graphene nanosheets Ag@G with in-situ plasma-deposited Ag nanoparticles. Synthesis of S13 Au@DMSN / Ag@G; The Au@DMSN and Ag@G obtained in steps S11 and S12 are dispersed in deionized water and uniformly compounded to obtain the Au@DMSN / Ag@G composite material.

3. The nano-plastic detection method according to claim 2, characterized in that, In the step S11, Triethanolamine: Deionized water: Cetyltrimethylammonium bromide: Sodium salicylate: Tetraethyl orthosilicate = 0.65 - 0.70 g: 20 - 25 mL: 0.35 - 0.40 g: 0.16 - 0.17 g: 3 - 5 mL, in a mixed solution of HCl and ethanol, by volume ratio, HCl:ethanol = 1:9; the temperature for washing away the residual organic template is 70 - 90 °C; DMSN: Ethanol: Ammonia water: Deionized water: (3 - aminopropyl)triethoxysilane = 90 - 100 mg: 80 - 120 mL: 2 - 3 mL: 2 - 3 mL: 0.5 - 2 mL; The concentration of chloroauric acid solution is 200 mg / mL, the concentration of TSC solution is 1 w / v%, the concentration of NaBH4 solution is 0.1 M, by volume ratio, chloroauric acid:TSC:NaBH4 = 15 - 25: 90 - 110: 45 - 55; The mass percentage concentration of the said HCl is 38%.

4. The nano-plastic detection method according to claim 2, characterized in that, In the step S12, wherein, by weight ratio, graphene nanosheets G:AgNO3 = 10: 35 - 40.

5. The nano-plastic detection method according to claim 2, wherein In the step S13, by mass ratio, the mass ratio of Au@DMSN:Ag@G is 1 - 4: 4 - 1.

6. The nano-plastic detection method according to claim 1, wherein In the colloidal solution obtained in the step S2, the concentration of KI is 0.05 - 0.25 M.

7. The nano-plastic detection method according to claim 1, characterized in that, The concentration of the Au@DMSN / Ag@G solution is 0.15 - 1.5 mg / mL.

8. The nano-plastic detection method according to claim 1, wherein The particle size of the said nanoplastics is 20 - 500 nm.

9. The nano-plastic detection method according to any one of claims 1-8, characterized in that, In the step S3, the SERS detection uses 1000 cm -1 as the characteristic peak.

10. The nano-plastic detection method according to claim 9, wherein, The said SERS detection includes qualitative detection and / or quantitative detection. The quantitative detection draws a relationship curve of the characteristic peak intensity and the nanoplastics concentration according to the Raman spectral intensity of the characteristic peak to determine the nanoplastics concentration of the sample to be detected.

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