Au@DMSN / Ag@G composite material and preparation method thereof

Abstract

The present invention belongs to the field of nanoplastics detection and specifically relates to an Au@DMSN / Ag@G composite material and its preparation method. Gold nanoparticles with adjustable interparticle gaps are semi-compatible incorporated into the inner surface of the pores of dendritic mesoporous silica (DMSN); silver nanoparticles are in situ deposited on highly conductive graphene nanosheets. Subsequently, the two components are combined by electrostatic attraction to obtain the Au@DMSN / Ag@G composite material. The resulting composite material can be used as a SERS substrate, capable of detecting PS NPs in a size range of 200-500 nm. Compared with current nanoplastics analysis methods, this composite substrate material has the advantages of high sensitivity, anti-interference, good repeatability, and strong quantitative analysis capabilities. In addition, it achieved a good recovery rate in lake water labeling experiments.

Description

Technical Field

[0001] The present invention relates to the field of nanoplastic detection, and in particular to an Au@DMSN / Ag@G composite material and a preparation method thereof. Background Art

[0002] The ubiquity of microplastics (1μm-5 mm) and nanoplastics (<1000 nm) in aquatic environments has garnered widespread global attention. Compared to microplastics, nanoplastics are particularly harmful, primarily due to their high surface area, which makes them susceptible to adsorbing organic pollutants, heavy metals, pathogenic microorganisms, and plastic additives released during degradation. To proactively address and prevent the harm posed by nanoplastics to humans, monitoring nanoplastics in aquatic environments is essential.

[0003] Currently, a variety of complex techniques are used to analyze and detect micro- and nanoplastics, including pyrolysis-gas chromatography / mass spectrometry (Pyrolysis-GC / MS), attenuated total reflectance infrared spectroscopy (ATR-FTIR), transmission electron microscopy (TEM), biosensors, and Raman spectroscopy. While these methods can quantitatively detect plastics in the environment, they also suffer from complex procedures, time-consuming processes, and destructive analysis. Biosensor methods are often sensitive to pH, making the results unreliable when analyzing samples under complex environmental conditions. Raman spectroscopy can accurately identify the molecular structure fingerprint of nanoplastic surfaces. Unfortunately, classical Raman spectroscopy is limited by its limited spatial resolution and interference from sample fluorescence.

[0004] Surface-enhanced Raman spectroscopy (SERS) is renowned for its high sensitivity. It amplifies Raman signals from molecules within the local electric field of nanoscale metal substrates, facilitating the detection of molecules at extremely low concentrations. However, due to the inherently low-scattering interfaces of various nanoplastics, the SERS signal obtained for nanoplastic detection is generally considered weak, making its application to nanoplastic detection challenging. Developing new SERS substrates to improve detection efficiency is often a laborious and time-consuming process, and achieving ultra-low concentration detection of nanoplastics in water remains challenging. Currently, SERS signal amplification is achieved by enhancing the local electromagnetic field of noble metal nanoparticles. Many research groups have successfully used noble metal nanoparticle-functionalized SERS substrates to detect micro- and nanoplastics. For example, Sang-Woo Joo et al. designed a method to prepare Au NSs@Ag@AAO SERS substrates by ultrasound-induced self-assembly and achieved ultrasensitive detection of submicron PS plastics. Based on the former, Jing Yu et al. designed an AAO / MoS2 / Ag coating structure with MoS2 particles as Raman internal standard, which achieved the Raman detection of NPs (<300 nm) and Hg 2+ However, common SERS substrates may have uneven hotspot distribution, resulting in a lack of reliability and consistency in SERS spectral signals. Wei Zhang et al. developed a ZnO nanorod array SERS substrate modified with Ag NPs on polydimethylsiloxane to simulate dragonfly wings. The substrate has the advantages of high sensitivity and signal repeatability, and realizes 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 nanoparticle suspension) are 50 μg / mL and 25 μg / mL, respectively. In order to deal with ultra-low concentrations of nanoplastics in aquatic environments (at 10 -9 -10 -4 g / mL) in real-world scenarios, it is necessary to develop a new type of SERS substrate to improve the sensitivity and accuracy of nanoplastic detection, so as to meet the detection needs of nanoplastics in aquatic environments as much as possible. Summary of the Invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present invention provides an Au@DMSN / Ag@G composite material and a preparation method thereof, which can be used as a SERS substrate for the detection of nanoplastics.

[0006] The specific technical solutions of the present invention are as follows:

[0007] The first aspect of the present invention provides a method for preparing an Au@DMSN / Ag@G composite material, comprising the steps of:

[0008] S1 Preparation of Au@DMSN,

[0009] S11 Synthesis of dendritic mesoporous silica DMSN,

[0010] Triethanolamine and deionized water are mixed and stirred at 70-90°C, and then cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal) are added and the reaction is continued with stirring. Then, tetraethyl orthosilicate (TEOS) is added dropwise to the above solution and the reaction is stirred at 75-85°C. After the reaction is completed, the solution 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).

[0011] S12 Amino modification of DMSN,

[0012] First, the dendritic mesoporous silica DMSN 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;

[0013] Synthesis of S13 Au@DMSN,

[0014] The DMSN-NH2 synthesized in step S12 was dispersed in ultrapure water, and then chloroauric acid solution was added in an ice-water bath and stirred for reaction. Then, trisodium citrate solution was added under vigorous stirring, and then freshly prepared NaBH4 solution was quickly added and the reaction continued. After the reaction was completed, the Au@DMSN powder was obtained by centrifugation, washing, and drying.

[0015] S2 Preparation of Ag@G;

[0016] 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.

[0017] S3 Synthesis of Au@DMSN / Ag@G;

[0018] The Au@DMSN and Ag@G obtained in steps S1 and S2 are dispersed in deionized water and uniformly compounded to obtain the Au@DMSN / Ag@G composite material.

[0019] The present invention semi-compatiblely incorporates gold nanoparticles (Au NPs) with adjustable interparticle gaps into the inner surface of the pores of dendritic mesoporous silica (DMSN); in-situ deposits silver nanoparticles (Ag NPs) on highly conductive graphene nanosheets (G), and composites the two through electrostatic attraction to prepare Au@DMSN / Ag@G composite materials. This can be used to manufacture SERS active substrates for the detection of nanoplastics.

[0020] Preferably, in step S11, triethanolamine: deionized water: hexadecyltrimethylammonium bromide: sodium salicylate: ethyl 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, according to a volume ratio of HCl: ethanol = 1:9, the temperature for washing away the residual organic template is 70-90°C;

[0021] The mass percentage concentration of the HCl is 38%.

[0022] Preferably, in step S12, 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.

[0023] Preferably, in step S13, 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 the volume ratio is chloroauric acid: TSC: NaBH4 = 15-20: 90-110: 45-55.

[0024] Preferably, in step S13, ethanol is used for washing and the drying temperature is 30-50°C.

[0025] Preferably, in step S2, the mass ratio of graphene nanosheets G:AgNO3 is 10:36.

[0026] Preferably, in step S3, the mass ratio of Au@DMSN:Ag@G is 1-4:4-1.

[0027] Another aspect of the present invention further provides an Au@DMSN / Ag@G composite material prepared by the preparation method.

[0028] The beneficial effects of the present invention are:

[0029] The Au@DMSN / Ag@G composite material prepared by the present invention can be used to manufacture SERS-active substrates. This composite overcomes the limitations of traditional two-dimensional substrates through the synergistic effect of gold and silver. Furthermore, due to the simultaneous use of two-dimensional and three-dimensional materials with high specific surface areas, the metal nanoparticles incorporated into its surface exhibit remarkable flexibility, allowing for more contact space between the active substrate and the analyte. This helps improve the detection strength and sensitivity of SERS detection, enabling quantitative detection of ultra-low concentrations and qualitative analysis of a wide range of PS NPs in various environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a reaction flow chart of the Au@DMSN / Ag@G composite material of the present invention;

[0031] Figure 2 Wide-angle XRD diffraction patterns of DMSN, Au@DMSN, G, Ag@G, Au, and Ag;

[0032] Figure 3 UV-visible absorption spectra, where (a) is the UV-visible absorption spectra of DMSN and Au@DMSN, and (b) is the UV-visible absorption spectra of G and Ag@G;

[0033] Figure 4 High-resolution XPS spectra, where (a) is the high-resolution XPS spectra of Au@DMSN, Ag@G and Au@DMSN / Ag@G; (b) is the high-resolution XPS spectra of Ag 3d, (c) Au 4f is the high-resolution XPS spectra, and (d) is the high-resolution XPS spectra of N 1s;

[0034] Figure 5 are transmission electron micrographs, where (af) are transmission electron micrographs of Au@DMSN, and (gl) are transmission electron micrographs of Ag@G;

[0035] Figure 6 are scanning electron microscopy images, where (a, b) are scanning electron microscopy images of DMSN, and (c) is a scanning electron microscopy image of Au@DMSN / Ag@G;

[0036] Figure 7The infrared spectra, N2 adsorption-desorption isotherms and pore size distribution of DMSN and DMSN-NH2, the Zeta potential distribution of DMSN, DMSN-NH2 and Au@DMSN, and the thermogravimetric characterization of Au@DMSN, Ag@G and Au@DMSN / Ag@G, where (a) is the infrared spectra of DMSN and DMSN-NH2, (b) is the Zeta potential distribution of DMSN, DMSN-NH2 and Au@DMSN, (c) is the N2 adsorption-desorption isotherms and pore size distribution of DMSN and DMSN-NH2; (d) is the thermogravimetric characterization of Au@DMSN, Ag@G and Au@DMSN / Ag@G;

[0037] Figure 8 Raman spectra of Au@DMSN / Ag@G and PS and the test results of PS NPs with different particle sizes, where (a) is the Raman spectra of Au@DMSN / Ag@G and PS, and (b) is the test results of PS NPs with different particle sizes;

[0038] Figure 9 is the particle size distribution diagram of the test sample PS NPs;

[0039] Figure 10 The Raman spectra of the samples of Examples 1 to 7 (with different precursor material ratios) and the 1000 cm -1 The SERS intensity results at 1000 cm-1 are shown in Figure 2; (a) is the Raman spectra of different samples of 200-500 nm PS NPs (0.05 mg / mL), and (b) is the Raman spectra of 1000 cm-1 in (a). -1 Related SERS intensity results at ;

[0040] Figure 11 Statistical graph of the detection results of PS NPs with different concentrations using the samples of Example 1 and Comparative Examples 1-5 as substrates;

[0041] Figure 12 SERS spectra of 200-500 nm PS NPs at different concentrations and the linear relationship between the SERS intensity of 200-500 nm PS NPs at 1000 cm-1 and concentration, where (a) is the SERS spectra of 200-500 nm PS NPs at different concentrations, (b) is the linear relationship between the SERS intensity of 200-500 nm PS NPs at 1000 cm-1 and concentration;

[0042] Figure 13 is 10 -2The SERS intensity results of PS NPs (10 mg / mL) in the presence of different interfering substances, the dual-component SERS spectra of PS and PMMA, PS NPs (10 -2 mg / mL) at 22 different random sites on the Au@DMSN / Ag@G substrate; and experimental reproducibility analysis results, where (a) is 10 -2 mg / mL of PS NPs in the presence of different interfering substances; (b) is the SERS spectrum of the two-component PS and PMMA; (c) is the SERS spectrum of PS NPs (10 -2 mg / mL) at 22 different random sites on the Au@DMSN / Ag@G substrate; (d) is the experimental reproducibility analysis result;

[0043] Figure 14 Figure 3 shows the locations of different sampling points for SERS testing of actual water samples, as well as blank Pearl River matrix test images and spiked test results of water samples at different sampling points. (a) shows the location of the sampling point in the Pearl River waters, (b) the sampling point in Dadonghai Tourist Area, Sanya City, and (c) the sampling point in the suburbs of Ningyuan County, Yongzhou City. (d) shows the blank Pearl River matrix test image, (e) shows the spiked test results of high-salinity seawater samples in Dadonghai Tourist Area, and (fg) shows the spiked test results of well water and contaminated water samples in the suburbs of Ningyuan County.

[0044] Figure 15 UV-visible absorption spectra and linear correlation of 200-500 nm PS NPs at different concentrations, where (a) is the UV-visible absorption spectra of 200-500 nm PS NPs at different concentrations, and (b) is the linear correlation. DETAILED DESCRIPTION

[0045] 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.

[0046] 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.

[0047] Unless otherwise specified, the reagents, materials, and equipment used in the examples of the present invention are all commercially available; the experimental methods, unless otherwise specified, are all conventional experimental methods in the art.

[0048] Chemicals and Materials

[0049] Triethanolamine (TEA, analytical grade), cetyltrimethylammonium 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%), polyvinylpyrrolidone (PVP, average molecular weight 58,000), ethylene glycol (analytical grade).

[0050] Instruments and equipment:

[0051] Transmission electron microscopy (TEM) images were obtained from a FEI Talos F200X transmission electron microscope; XPS spectra were obtained from a Shimadzu AXIS SUPRA X-ray photoelectron spectrometer; field emission scanning electron microscopy (SEM) images were obtained from a Zeiss Ultra 55 scanning electron microscope; Fourier transform infrared spectra were obtained from a Spectrum Two infrared analyzer; UV-visible spectra were obtained from a Shimadzu UV2700 spectrophotometer; X-ray powder diffraction (XRD) patterns were obtained from an Ultima IV X-ray diffraction analyzer; thermogravimetric analysis patterns were obtained from a Netzsch TG-209F3 thermogravimetric analyzer; BET surface area and pore size analysis patterns were obtained from a Quantachrome ASiQwin surface area analyzer; zeta potential data were obtained from a Malvern Zeta potential analyzer; and Raman spectra were obtained from a Horiba confocal laser microscope Raman spectrometer.

[0052] Example 1 Preparation of Au@DMSN / Ag@G composite material

[0053] refer to Figure 1 The preparation of Au@DMSN / Ag@G composite materials includes the following steps:

[0054] Preparation of S1 Au@DMSN

[0055] S11 Preparation of Dendritic Mesoporous Silica (DMSN)

[0056] 0.68 g of TEA was added to a glass flask containing 25 mL of deionized water and stirred in an 80°C oil bath for 30 minutes. Then, 0.38 g of CTAB and 0.168 g of NaSal were added. After stirring for 1 hour, 4 mL of TEOS was added dropwise to the mixture using a micropipette and stirred at 80°C for another 2 hours. After the reaction, the product was collected by centrifugation at 9000 rpm for 10 minutes and washed twice with ethanol and twice with deionized water to remove residual reactants. The precipitate was then washed three times (24 hours each time) with a mixture of HCl and ethanol (HCl:ethanol = 1:9 v / v) at 80°C with stirring to remove residual organic template. Finally, the product was dried under vacuum at 50°C for 12 hours to obtain a white solid sample.

[0057] -NH2 modification of S12 DMSN

[0058] First, 100 mg of DMSN was dispersed in 100 mL of ethanol and ultrasonicated for 10 minutes, followed by stirring for 15 minutes. Then, 2.5 mL of ammonia water, 2.5 mL of deionized water, and 1 mL of APTES were added to the solution under vigorous stirring. Vigorous stirring was continued for 12 hours. Finally, the final product was washed several times with ethanol and dried in a vacuum at 50°C overnight to obtain DMSN-NH2 powder.

[0059] Preparation of S13 Au@DMSN

[0060] The DMSN-NH2 synthesized in S12 was dispersed into 20 mL of ultrapure water via ultrasonic treatment. Then, 20 μL of a 200 mg / mL chloroauric acid solution was added in an ice-water bath. Stirring continued for 1 hour. Then, 100 μL of a 1% TSC solution was added under vigorous stirring, followed by 50 μL of a freshly prepared 0.1 M NaBH4 solution. The reaction continued for 1 hour. After the reaction, the product was collected by centrifugation at 8000 rpm for 5 minutes, washed three times with ethanol, and dried at 40°C overnight to obtain Au@DMSN powder.

[0061] Preparation of S2 Ag@G

[0062] Weigh 10 mg of G (graphene nanosheets) and add it to a 50 mL glass flask containing 10 mL of deionized water, sonicate for 5 minutes, and then heat it to a constant temperature of 85°C; weigh 36 mg of AgNO3, dissolve it in 5 mL of water, and then add it to the above precursor solution and keep stirring. After reacting for 15 minutes, heat it to a constant temperature of 90°C, and then add 4 mL of 1% trisodium citrate solution and keep reacting for 40 minutes. After the reaction is completed, wash it with ethanol and water, disperse it in deionized water, and store it at low temperature for use.

[0063] S3 Au@DMSN / Ag@G

[0064] According to m Au@DMSN With m Ag@G The mass ratio of Au@DMSN and Ag@G was 2:1. Appropriate amounts of Au@DMSN and Ag@G were weighed and dispersed in deionized water. The mixture was magnetically stirred for 30 min. After the materials were uniformly composited, they were precipitated by centrifugation. Finally, the prepared Au@DMSN / Ag@G material was redissolved in deionized water.

[0065] Examples 2-7

[0066] The difference from Example 1 is that in step S3, the following steps are followed: Au@DMSN With m Ag@G The mass ratio of Au@DMSN and Ag@G was 1:4, 1:3, 1:2, 1:1, 3:1, and 4:1. Appropriate amounts of Au@DMSN and Ag@G were weighed for the final synthesis of Au@DMSN / Ag@G, and the rest were the same.

[0067] Comparative Example 1

[0068] Referring to step S2 of Example 1, Ag@G was prepared.

[0069] Comparative Example 2

[0070] Referring to step S1 of Example 1, Au@DMSN was prepared.

[0071] Comparative Example 3

[0072] Referring to step S11 of Example 1, DMSN was prepared.

[0073] Comparative Example 4

[0074] Au NPs were synthesized using the citric acid reduction method. Specifically, 24 μL of a 200 g / L aqueous solution of chloroauric acid tetrahydrate was added to 50 mL of distilled water. The solution was placed in a 120°C water bath and heated to boiling with stirring. Then, 0.5 mL of a 1% trisodium citrate solution was quickly added. The reaction was continued for 30 minutes until the solution turned a stable wine red. Heating was stopped and the solution was allowed to cool to room temperature for later use.

[0075] Comparative Example 5

[0076] To synthesize Ag NPs, 0.3 g of polyvinylpyrrolidone (PVP) was dissolved in 17 mL of ethylene glycol at room temperature, then heated in a 160°C oil bath with stirring. Subsequently, 110 mg of AgNO₃ was dissolved in 3 mL of ethylene glycol and slowly added dropwise to the PVP solution. Heating was continued for 30 minutes. After the reaction, the mixture was centrifuged at 9000 rpm for 10 minutes. The resulting Ag nanoparticles (Ag NPs) were washed twice with ethanol and redispersed in 20 mL of ethanol.

[0077] Performance testing and characterization:

[0078] 1. Material Characterization

[0079] 1. XRD analysis

[0080] XRD is a commonly used characterization method to verify the immobilization and crystallinity of nanoparticles. Therefore, XRD analysis was performed on DMSN, Au@DMSN, G, and Ag@G, and their wide-angle XRD diffraction patterns are shown in Figure 2. Figure 2 As 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).

[0081] 2. UV-visible absorption spectrum

[0082] 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 3As shown in Figures (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.

[0083] 3. XPS analysis

[0084] 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 The a in the figure indicates 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 combined, the carbon content significantly increases, which 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 Figure 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 / 2 The 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 4(b) indicates that AgNPs have been successfully loaded onto the surface of the graphene nanosheets (G). Figure 4 Figure 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 4As shown in Figure d, during the modification process, the formation of -NH- and N-Au bonds is consistent with the literature, and the -NH2 content decreases. This phenomenon strongly confirms that the AuNPs 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 AuNPs 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.

[0085] TEM analysis TEM images ( Figure 5 Figures af) in Figure 5 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 AuNPs. The EDS elemental map shows that Si, O, and Au elements are evenly distributed on the Au@DMSN matrix, which further proves the successful loading of Au nanoparticles. Figure 5 gl 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 AuNPs and Ag NPs 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.

[0086] 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 Panels c and 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.

[0087] Infrared and adsorption analysis 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 pores on the surface of DMSN. Figure 7 Figure a shows the FTIR characteristic spectra of DMSN before and after amino modification, showing the weak symmetric stretching vibration of CH at 2850-2950 cm -1This 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.

[0088] Figure 7 As shown in Figure 7(b), the zeta potential changes of DMSN, DMSN-NH2, and Au@DMSN indicate that the unmodified DMSN surface is negatively charged and rich in Si-OH groups, with a potential 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 45.1mV±1.6mV. 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 shows a type IV isotherm (Figure 7(c), 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 is reduced to 0.937cm 3 / g, indicating that APTES successfully coated DMSN. This unique pore structure provides sufficient compatible space for loading precious metal nanoparticles.

[0089] 7. Thermogravimetric analysis

[0090] like Figure 7The d in the figure represents the thermogravimetric characterization of Au@DMSN, Ag@G, and Au@DMSN / Ag@G. The thermogravimetric curves of Ag@G and Au@DMSN / Ag@G are broadly similar. This indicates that Au@DMSN, due to its high-molecular-weight carbon and silicon polymer carrier, exhibits a degree of thermal stability, leading to carbonization from the outer surface to the inner surface. When the temperature rises to 180°C, G begins to thermally decompose, generating CO and CO₂. Analysis of the residue mass fraction indicates the successful composite of Au@DMSN and Ag@GNS.

[0091] 2. PS NPs Detection

[0092] 1. Determine characteristic peaks

[0093] Sample Preparation: The Au@DMSN / Ag@G prepared in Example 1 was mixed with PS NPs. KI solution was then added as an aggregating agent. After thorough mixing, the solution was allowed to stand for 1 hour to form a stable colloidal solution. Finally, 20 μL of the mixed solution was dropwise added to a 5×5 mm silicon wafer using a glass micropipette and dried in an oven at 50°C for 1 hour. The dried sample was subjected to SERS analysis. The resulting Raman spectra were baseline-corrected.

[0094] Normal Raman and SERS spectra were obtained by confocal laser microscope Raman spectrometer and 564 nm (3.5%) laser. During the Raman spectrum acquisition process, a 50x objective lens was selected and the acquisition wavelength range was 400–1700 cm -1 There are 3 accumulations in 5s acquisition time.

[0095] Raman scattering tests were performed on PS NPs with a particle size distribution range of 200-500 nm. Figure 8 As shown in a, the two most prominent characteristic peaks are located at 1000 cm -1 and 1030 cm -1 The positions correspond to the breathing vibration peak of the benzene ring and the CH in-plane deformation, respectively. -1 There is a low peak at 1000 cm -1 It is the strongest characteristic peak, and the concentration of PS NPs is reflected by comparing the intensity of this peak.

[0096] In addition, it can be seen that Au@DMSN / Ag@G as the substrate has a high -1 and 1030 cm -1 There is no signal nearby, and its interference with the detection of PS NPs can be ruled out.

[0097] Secondly, by Figure 8 As shown in (b), for the same mass concentration of PS NPs, Au@DMSN / Ag@G can also -3 In summary, it can be seen that the Au@DMSN / Ag@G prepared in the embodiment of the present invention can detect PS NPs with a particle size of 50-100 nm and 20 nm.

[0098] Plastics in the actual environment have the characteristic of differential particle size distribution. The study of PS NPs with a wide distribution range is more innovative and representative. Here, dynamic light scattering (DLS) experiments were carried out on PS NPs with a wide particle size distribution range as the main research object. Figure 9 ), demonstrating that the particle size distribution of PS NPs is primarily in the 200-500 nm range. Furthermore, due to their small nanoscale size, they can enter the hotspot gaps of the SERS composite material, undergoing inter-plastic attractive deposition. Furthermore, because the standard Raman characterization signals of 50-100 nm and 20 nm PS suspensions are smaller than those of 200-500 nm PS suspensions, subsequent experiments selected 200-500 nm PS for detection, as they exhibit a more advantageous SERS signal.

[0099] 2. Comparison of test results of materials synthesized in Examples 1-7

[0100] SERS measurements were performed using 200-500 nm PS NPs (0.05 mg / mL) as performance probes and Au@DMSN / Ag@G synthesized in Examples 1-7 as substrates.

[0101] The results are as follows Figure 10 a, b in the figure represent 1000 cm -1 The SERS intensity at m Au@DMSN :m Ag@G The intensity of the PS NPs increased dramatically with the increase of the volume ratio, from 529 at a ratio of 1:4 to 1581 at a ratio of 2:1. However, a further increase in the volume ratio resulted in a decrease in intensity. Therefore, the optimal response was shown at a ratio of 2:1 in Example 1. This may be attributed to the fact that the increase in the amount of Au@DMSN compensated for the lack of Raman hotspots of Ag@G in the three-dimensional space, but then the excessive amount of Au@DMSN presumably hindered the contact between PS NPs and the SERS composite substrate.

[0102] 3. Comparison of the detection effects of each sample in Example 1 and Comparative Examples 1-5

[0103] The SERS tests were performed on the samples in Example 2 and Comparative Examples 1-5 using 10 μg / mL and 1 μg / mL PS NPs as probes, respectively. The results are shown in Figure 2. Figure 11 As shown in the figure, it can be seen that DMSN and graphene nanosheets (G) cannot enhance the SERS signal due to their non-plasmonic structures and cannot detect PS NPs. Au NPs and Ag NPs, as plasmonic materials, can interact with the surface of PS NPs through hydrophobic / electrostatic effects and produce SERS enhancement, but are limited by the weak signal characteristics of PS NPs themselves, and only weak characteristic peaks can be detected at a concentration of 10 μg / mL. Thanks to the dendritic multi-mesoporous structure and high specific surface area of ​​DMSN, Au@DMSN forms a three-dimensional satellite 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 hotspot distribution.

[0104] 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.

[0105] 4. Quantitative Detection and Evaluation of PS NPs in the Samples of Example 1

[0106] Using the sample of Example 1, PS NPs of different standard concentrations were tested according to the following conditions, specifically:

[0107] V Au@DMSN / Ag@G :VPS NPs =4:4, V Au@DMSN / Ag@G Concentration 1.125 mg / mL;

[0108] The KI concentration in the colloidal solution was 0.10 mol / L;

[0109] 4.1 Quantitative analysis

[0110] PS NPs with different concentrations and a wide range of particle size distribution (200-500 nm) were tested, and the 1000 cm -1 The Raman peaks were used as the characteristic peaks of PS for quantitative analysis. The relationship curve between the characteristic peak intensity I and the logarithm of PS concentration (logC) was drawn according to the Raman spectrum intensity of the characteristic peaks, and a quantitative analysis method was established, such as Figure 14 As shown in a and b.

[0111] according to Figure 12 a and b in the figure indicate that with the increase of PS NPs concentration, the SERS intensity increases significantly, and its detection limit is 10 −4 mg / mL. The relationship curve between the characteristic peak intensity I and the logarithm of PS concentration (logC) was further drawn based on the Raman spectrum intensity of the characteristic peak. The linear concentration range was 10 −4 -10 −1 mg / mL, 1000 cm -1 The SERS intensity at 400 nm showed a good linear relationship with the logarithm of mass concentration, and the linear fitting equation was y = 527.20x +2318.26, R 2 = 0.996.

[0112] 4.2 Uniformity, Anti-interference and Selectivity Evaluation

[0113] PS standard solution was used to evaluate the anti-interference, uniformity, selectivity and reliability of the detection.

[0114] (1) Anti-interference: The main salt interference substances in the ocean, such as NaCl, KCl, CaCl2, MgCl2 and glucose, were used to simulate the interference environment of a single series of salts in the water-salt environment. PS (200-500 nm, 10 −2 mg / mL) signal.

[0115] The results are as follows Figure 13 As shown in a, it shows that in the interference environment of a single series of salts (0.8 mg / mL Ca 2+ , 58 mg / mL Na + , 1.1 mg / ml Mg 2+ , 1.6 mg / ml K +, 2 mg / mL glucose), the SERS intensity of PS was less disturbed. This shows that the detection method based on the Au@DMSN / Ag@G SERS substrate of the present invention can still effectively identify and detect PS in the presence of interfering substances.

[0116] (2) Selectivity: Select PS (200-500 nm, 10 −2 mg / mL) was mixed with PMMA (300 nm, 1 mg / mL) for SERS detection.

[0117] like Figure 13 Figure b depicts the characteristic spectrum of PS NPs (1000 cm -1 ) and PMMANPs (596, 816 cm −1 ) were detected separately. When they were mixed together, these characteristic Raman peaks remained, with no noticeable peak shift. These results demonstrate that the detection method of this invention can distinguish the content of nanoplastic characteristic peaks in a mixture and can be used to detect different types of nanoplastics in complex environments.

[0118] (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 locations on the silicon wafer.

[0119] The results are as follows Figure 13 As shown in Figure c, there is no significant difference in the SERS spectra of different detection sites. -1 The response intensities of the characteristic peaks at the α-D-type ...

[0120] 4.3 Practicality and Accuracy

[0121] Different concentrations of PS NPs (200-500 nm) were added to lake water (collected from the Pearl River Lake in summer). The samples were allowed to stand overnight and the supernatant was collected and used directly without further processing.

[0122] (1) Practicality

[0123] First, a certain volume of Pearl River water was allowed to stand overnight, and the supernatant was collected for later use. A certain volume of PS solution was measured and prepared to 100 μg / mL, 10 μg / mL, 2 μg / mL, 1 μg / mL, and 0.5 μg / mL. Equal volumes were then added to the Au@DMSN / Ag@G solution. 20 μL of 0.1 M KI was then added, shaken, and allowed to incubate for 1 hour. After the incubation, 20 μL was dripped onto a silicon wafer, dried at 50°C for 30 minutes, and then subjected to SERS analysis.

[0124] Pearl River water was collected in the summer, at the location shown in Figure 14(a). After the sample was allowed to stand overnight, the supernatant was used directly without further treatment. As shown in Figure 14(d), the aforementioned detection method did not detect a SERS signal response in the initial water sample. Therefore, a spike recovery experiment was conducted on PS NPs, and the results are shown in Table 1. The recoveries of PS NPs ranged from 91.18% to 109.27%, with RSDs (n=3) ranging from 3.24% to 11.66%.

[0125] In addition, simple simulated spike tests were conducted on nearshore seawater from the Dadonghai Tourist Area in Sanya City, underground well water from the suburbs of Ningyuan County in Yongzhou City, and water samples from nearby contaminated ditches. The sampling locations are shown in Figure 14 (b) and (c). Further analysis revealed that no characteristic signal of PS NPs was detected at 1000 cm⁻¹. Therefore, a simulated concentration of 0.5 μg / mL of PS NPs was added to the above-mentioned actual water samples. As shown in Figure 14 (eg), all added nanoplastics were detected by the SERS substrate. The above results demonstrate that the SERS substrate prepared in this embodiment of the present invention overcomes the difficult problem of the high detection limit of nanoplastics in saltwater and contaminated environments using SERS technology, and also demonstrates that the prepared SERS substrate has excellent environmental adaptability.

[0126] (2) Accuracy

[0127] The accuracy was evaluated by UV-visible spectrophotometry.

[0128] First, a linear equation was established for the absorbance intensity and concentration of PS NPs with a particle size range of 200-500 nm. Based on this, a lake water spike test was conducted using UV-visible spectrophotometry and compared with the proposed SERS method.

[0129] like Figure 15(a) and (b) in the figure. The UV-Vis spectrophotometer has a very small RSD value, but the recovery rate fluctuates greatly, ranging from 49.83% to 134.95%. Clearly, the UV-Vis spectrophotometer method is not suitable for measuring PS concentrations in real water samples.

[0130] Table 1. Results of spiked recovery experiments on actual environmental water samples

[0131]

[0132] These results confirm the superiority and feasibility of the detection method of the present invention in real aquatic environment detection.

[0133] In summary, this invention rationally designs a two-dimensional planar substrate with excellent electrical conductivity and simultaneously supports plasmonic Ag NPs. Furthermore, based on the Stober mechanism and sol-gel strategy, a semi-compatible porous structure of DMSN embedded with Au NPs is synthesized. The precursor materials are then combined via electrostatic attraction to successfully prepare an Au@DMSN / Ag@G composite. This composite serves as a substrate capable of detecting PS NPs in a size range of 200-500 nm. Compared to existing nanoplastic analysis methods, this substrate offers advantages such as high sensitivity, interference resistance, excellent reproducibility, and robust quantitative analysis capabilities. Furthermore, good recovery rates were achieved in lake water labeling experiments.

[0134] The technical features of the above-described embodiments can be combined in any combination. To simplify the description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. It should be pointed out that for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent of this invention shall be based on the attached claims.

Claims

1. A method for preparing Au@DMSN / Ag@G composite material, characterized in that: Including steps: S1 Preparation of Au@DMSN, S11 Synthesis of dendritic mesoporous silica DMSN, Triethanolamine and deionized water are mixed and stirred at 70-90°C, and then hexadecyltrimethylammonium bromide and sodium salicylate are added. The mixture is stirred and reacted to form a solution. Then, ethyl orthosilicate is added dropwise to the solution. The mixture is stirred and reacted 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 vacuum dried to obtain dendritic mesoporous silica DMSN. S12 Amino modification of DMSN, First, the dendritic mesoporous silica DMSN 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; Synthesis of S13 Au@DMSN, The DMSN-NH2 synthesized in step S12 was dispersed in ultrapure water, and then chloroauric acid solution was added in an ice-water bath and stirred for reaction. Then, trisodium citrate solution was added under vigorous stirring, and then freshly prepared NaBH4 solution was quickly added and the reaction continued. After the reaction was completed, the Au@DMSN powder was obtained by centrifugation, washing, and drying. S2 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. S3 Synthesis of Au@DMSN / Ag@G; The Au@DMSN and Ag@G obtained in steps S1 and S2 are dispersed in deionized water and uniformly compounded to obtain the Au@DMSN / Ag@G composite material.

2. The method for preparing the Au@DMSN / Ag@G composite material according to claim 1, characterized in that: The pore size range of the DMSN synthesized in step S11 is 10-33 nm.

3. The method for preparing the Au@DMSN / Ag@G composite material according to claim 1, wherein: In the step S11, Triethanolamine: deionized water: hexadecyltrimethylammonium bromide: sodium salicylate: ethyl orthosilicate = 0.65-0.7g: 20-25 mL: 0.35-0.40 g: 0.16-0.17 g: 3-5 mL.

4. The method for preparing the Au@DMSN / Ag@G composite material according to claim 1, wherein: In step S11, the mixed solution of HCl and ethanol has a volume ratio of HCl:ethanol = 1:9; the temperature for washing away the residual organic template is 70-90°C; The mass percentage concentration of the HCl is 38%.

5. The method for preparing the Au@DMSN / Ag@G composite material according to claim 1, wherein: In the step S12, DMSN: ethanol: ammonia: deionized water: (3-aminopropyl)triethoxysilane = 90-100 mg: 80-120 mL: 2-3 mL: 2-3 mL: 0.5-2 mL.

6. The method for preparing the Au@DMSN / Ag@G composite material according to claim 1, wherein: In step S13, the concentration of the chloroauric acid solution is 200 mg / mL, the concentration of the trisodium citrate solution is 1 w / v%, and the concentration of the NaBH4 solution is 0.1 M. According to the volume ratio, the chloroauric acid: TSC: NaBH4 = 15-25: 90-110: 45-55.

7. The method for preparing the Au@DMSN / Ag@G composite material according to claim 6, characterized in that: In step S13, ethanol is used for washing, and the drying temperature is 30-50°C.

8. The method for preparing the Au@DMSN / Ag@G composite material according to claim 1, wherein: In step S2, according to the mass ratio, graphene nanosheets G:AgNO3=10:35-40.

9. The method for preparing the Au@DMSN / Ag@G composite material according to claim 1, wherein: In step S3, the mass ratio of Au@DMSN:Ag@G is 1-4:4-1.

10. The Au@DMSN / Ag@G composite material prepared by the preparation method according to any one of claims 1 to 9.

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