Zr-PyDC@Au-Ag / GNS composite SERS substrate and its construction method and application

Abstract

The present invention belongs to the field of nanoplastic detection, and in particular relates to a Zr-PyDC@Au-Ag / GNS composite SERS substrate and its construction method and application. The construction method uses Zr-PyDC as a carrier of Au NPs. Because of its high porosity structure, noble metal nanoparticles can be evenly distributed in and near the pores to obtain Zr-PyDC@Au. Subsequently, Ag NPs are synthesized and loaded onto the Zr-PyDC@Au surface by an in-situ reduction synthesis method to obtain Zr-PyDC@Au-Ag. At the same time, graphene nanosheets are added and composited with the Zr-PyDC@Au-Ag / GNS composite substrate. Due to the characteristics of graphene itself, it can synergize with other SERS substrates to further enhance SERS detection performance. The relative deviation (RSD) of the prepared substrate test signal results is less than 10%, meeting the quantitative detection requirements.

Description

Technical Field

[0001] The present invention relates to the field of nanoplastic detection, and in particular to a Zr-PyDC@Au-Ag / GNS composite SERS substrate and a construction method and application thereof. Background Art

[0002] Currently, the detection technologies for nanoplastics mainly include microscopic imaging, mass spectrometry, and spectroscopy. Among them, surface-enhanced Raman scattering (SERS) technology is considered a powerful tool for nanoplastic analysis due to its single-molecule sensitivity, fingerprint recognition capabilities, and non-destructive detection characteristics. However, traditional SERS substrates (such as gold / silver nanosols) are easily interfered with by environmental ions and organic molecules in practical applications, resulting in poor signal repeatability. SERS substrates designed based on two-dimensional structures such as anodic aluminum oxide (AAO) have planar characteristics that limit the density of "hot spots" in three-dimensional space, making it difficult to achieve high-sensitivity detection of low-concentration PS NPs. To address the above problems, metal-organic framework (MOF) materials provide an ideal carrier for the loading of precious metal nanoparticles due to their high porosity, adjustable pore size, and ultra-large specific surface area. The three-dimensional, hierarchical pore structure of MOFs not only effectively anchors metal nanoparticles, forming a dense and evenly distributed SERS active site, but its abundant pores also enrich PS NPs through confinement, significantly increasing the probability of contact between the target and the "hotspot." Furthermore, the metal nodes or organic ligands of some MOFs can further enhance the Raman signal through chemical interactions, thus breaking through the sensitivity bottleneck of traditional substrates. Although MOF-based SERS materials have shown great potential in environmental analysis, their application in nanoplastic detection remains relatively unreported. Summary of the Invention

[0003] In view of the above-mentioned deficiencies in the prior art, the present invention constructs a Zr-PyDC loaded noble metal nanoparticle composite substrate for PS NPs detection, thereby broadening the research boundaries of SERS technology in environmental pollutant analysis.

[0004] The specific technical solutions of the present invention are as follows:

[0005] In a first aspect of the present invention, a method for constructing a Zr-PyDC@Au-Ag / GNS composite SERS substrate is provided, comprising the steps of:

[0006] S1 Synthesis of Zr-PyDC,

[0007] Dissolve zirconium chloride in DMF, then add concentrated hydrochloric acid, seal and stand in the dark for 0.5-2 hours, then add pyridine-2,5-dicarboxylic acid to the above solution and disperse until it is completely dissolved, then transfer the solution to a reactor and react at 110-130° C. for 15-25 hours. After the reaction, centrifuge to obtain a precipitate, wash, and dry to obtain the Zr-PyDC;

[0008] S2 Synthesis of Zr-PyDC@Au-Ag,

[0009] A chloroauric acid solution was added to an ethanol solution of Zr-PyDC under stirring, and the mixture was stirred for more than 5 hours. The precipitate was then centrifuged and redissolved in ethanol. A NaBH4 solution was then added dropwise under vigorous stirring. After the reaction, the mixture was centrifuged and washed to obtain Zr-PyDC@Au. The Zr-PyDC@Au was then dispersed in DMF, and silver nitrate was added to completely dissolve the mixture. The mixture was reacted at 110-130°C for 2-5 hours. After the reaction, the precipitate was centrifuged and washed to obtain Zr-PyDC@Au-Ag.

[0010] S3 Synthesis of Zr-PyDC@Au-Ag / GNS;

[0011] The graphene nanosheets GNS and the Zr-PyDC@Au-Ag obtained in step S2 were dispersed in DMF, stirred at 60° C., centrifuged to obtain a precipitate, and washed to obtain the Zr-PyDC@Au-Ag / GNS composite SERS substrate.

[0012] This scheme uses Zr-PyDC as a carrier for Au NPs. Its highly porous structure allows the noble metal nanoparticles to be evenly distributed within and near the pores of Zr-PyDC, resulting in Zr-PyDC@Au. Subsequently, Ag NPs are synthesized and loaded onto the surface of Zr-PyDC@Au via an in situ reduction synthesis method, resulting in Zr-PyDC@Au-Ag. The highly regular arrangement of the crystals reduces signal instability. Next, ordered graphene nanosheets are introduced. Graphene's inherent ultrahigh electrical conductivity allows for complexing with the Zr-PyDC@Au-Ag substrate, further enhancing the SERS substrate's detection performance while reducing potential fluorescence background interference from the Zr-PyDC.

[0013] In some embodiments of the present invention, in step S1, zirconium chloride: DMF: concentrated hydrochloric acid: pyridine-2,5-dicarboxylic acid = 115-118 mg: 3-8 mL: 3-8 mL: 82-85 mg.

[0014] In some embodiments of the present invention, in step S2, the concentration of the Zr-PyDC ethanol solution is 3-4 mg / mL, the concentration of the chloroauric acid solution is 180-220 mg / mL, and the concentration of the NaBH4 solution is 0.05-0.2 mol / L. In terms of volume ratio, the ethanol solution of Zr-PyDC: chloroauric acid solution: NaBH4 solution = 3:0.02:0.2; in terms of mass ratio, the Zr-PyDC: silver nitrate = 10:0.1~40; preferably, the Zr-PyDC: silver nitrate = 10:10.

[0015] In some embodiments of the present invention, in step S3, the mass ratio of graphene nanosheets GNS:Zr-PyDC@Au-Ag is 1:4.

[0016] The second aspect of the present invention provides a composite SERS substrate prepared by the above-mentioned construction method.

[0017] A third aspect of the present invention further provides a method for detecting nanoplastics based on the composite SERS substrate obtained by the above construction method, comprising the following steps:

[0018] A Zr-PyDC@Au-Ag / GNS solution was prepared and then mixed with a polystyrene nanoparticle suspension. KI was added as an aggregating agent. After the above solutions were thoroughly mixed, they were allowed to stand until the sample formed a stable colloidal solution for SERS detection.

[0019] In some embodiments of the present invention, the KI concentration in the colloidal solution is 0.01-0.025 mol / L, preferably, the KI concentration is 0.025 mol / L

[0020] In some embodiments of the present invention, the concentration of the Zr-PyDC@Au-Ag / GNS solution is 0.1-1 mg / mL. Preferably, the concentration of the Zr-PyDC@Au-Ag / GNS solution is 0.5 mg / mL.

[0021] In some embodiments of the present invention, the polystyrene nanoparticles have a particle size of 20-500 nm, such as 20 nm, 50-100 nm, 200-500 nm, etc.

[0022] In some embodiments of the present invention, the nanoplastic detection method includes qualitative detection and / or quantitative detection. The quantitative detection is to determine the nanoplastic concentration of the sample by plotting the relationship between the characteristic peak intensity and the nanoplastic concentration based on the Raman spectrum intensity of the characteristic peak. For example, in some preferred embodiments, for 20 nm PS NPs, the linear fitting equation y = 19.96x + 532.03, R 2=0.957; In some preferred embodiments, for 50-100 nm PSNPs, the linear fitting equation y = 12.82x + 711.31, R 2 =0.951; in some preferred embodiments, for 200-500 nm PS NPs, the linear fitting equation y = 15.03x + 702.04, R 2 =0.987; y is the characteristic peak intensity, x is the nanoplastic concentration.

[0023] The beneficial effects of the present invention are:

[0024] In the present invention, Zr-PyDC is used as a carrier of Au NPs. Due to its highly porous structure, noble metal nanoparticles can be evenly distributed in and near the pores of Zr-PyDC to obtain Zr-PyDC@Au. Subsequently, Ag NPs are synthesized and loaded onto the surface of Zr-PyDC@Au through an in situ reduction synthesis method to obtain Zr-PyDC@Au-Ag. At the same time, graphene nanosheets are added to composite it to prepare a Zr-PyDC@Au-Ag / GNS composite substrate, so that Zr-PyDC@Au-Ag is loaded on the dispersed graphene nanosheets. At the same time, due to the characteristics of graphene itself, it can synergize with other SERS substrates to further enhance the SERS detection performance.

[0025] The prepared Zr-PyDC@Au-Ag / GNS substrate can be used for ultrasensitive detection of polystyrene nanoparticle suspensions (20-500 nm, ppm level) in various aquatic systems, addressing a critical gap in quantifying trace amounts of nanoplastics with heterogeneous sizes and compositions. This method overcomes the limitations of traditional two-dimensional substrates through the synergistic effect of gold / silver, and the specific test signal results have a relative deviation (RSD) of less than 10%, meeting the requirements for quantitative detection. It is worth mentioning that KI was introduced during the detection process, utilizing its induced enrichment properties to enhance SERS performance. Finally, in actual water sample environmental testing, PS NPs were successfully detected in spiked water samples with recoveries ranging from 82.26% to 109.43% and RSDs ranging from 6.45% to 22.49%, enabling quantitative analysis of a wide range of environmentally diverse nanoplastics. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the synthesis of Zr-PyDC@Au-Ag / GNS;

[0027] Figure 2a is the XRD powder diffraction pattern of Zr-PyDC and UIO-66;

[0028] Figure 2b XRD powder diffraction patterns of Zr-PyDC, Zr-PyDC@Au, Zr-PyDC@Au-Ag, Zr-PyDC@Au-Ag / GNS and GNS;

[0029] Figure 3 Transmission electron microscopy images of Zr-PyDC@Au and Zr-PyDC@Au-Ag, where (a) (b) are transmission electron microscopy images of Zr-PyDC@Au, and (c) (d) (e) (f) (g) (h) are transmission electron microscopy images of Zr-PyDC@Au-Ag;

[0030] Figure 4 UV-visible absorption spectra of Zr-PyDC, Zr-PyDC@Au and Zr-PyDC@Au-Ag;

[0031] Figure 5 XPS spectra, where (a) is the full XPS spectrum of Zr-PyDC@Au-Ag, (b) is the high-resolution XPS spectrum of Au 4f, and (c) is the high-resolution XPS spectrum of Ag 3d;

[0032] Figure 6 N2 adsorption-desorption isotherms and pore size distribution of Zr-PyDC;

[0033] Figure 7 Thermogravimetric images of Zr-PyDC, Zr-PyDC@Au, Zr-PyDC@Au-Ag and Zr-PyDC@Au-Ag / GNS materials;

[0034] Figure 8 Raman spectra of Zr-PyDC@Au-Ag / GNS and PS NPs and SERS test results of PS NPs with different particle sizes; (a) is the Raman spectra of Zr-PyDC@Au-Ag / GNS and PS, and (b) is the test results of PS NPs with different particle sizes;

[0035] Figure 9 The comparison of the detection results of PS NPs samples with different amounts of silver nitrate in Examples 1-5, where (a) is the spectrum of 200-500 nm PS NPs (0.01 mg / mL) with different amounts of silver nitrate, and (b) is the spectrum of 1000 cm in Figure (a). -1 The corresponding SERS intensity map at ;

[0036] Figure 10 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;

[0037] Figure 11 The experimental results of KI dosage optimization are shown in Figure 1, where (a) is the SERS spectra of 200-500 nm PS NPs (0.01 mg / mL) at different KI molar concentrations, and (b) is the SERS spectra of 1000 cm in Figure 1. -1 The corresponding SERS intensity results at ;

[0038] Figure 12 Comparison of detection results at different SERS substrate concentrations, where (a) is the SERS spectra of 200-500 nm PS NPs (0.01 mg / mL) at different SERS substrate concentrations, and (b) is the SERS spectra at 1000 cm in (a). -1 The corresponding SERS intensity at

[0039] Figure 13 Raman spectra of PS NPs with particle size distribution of 20 nm, 50-100 nm, and 200-500 nm at different concentrations in the range of 1-100 μg / ml, as well as the linear relationship between concentration and characteristic peak intensity, detected based on Zr-PyDC@Au-Ag / GNS substrate, where (a) (b) are Raman spectra of PS NPs with particle size of 20 nm at different concentrations in the range of 1-100 μg / ml, as well as the linear relationship between concentration and characteristic peak intensity, (c) (d) are Raman spectra of PS NPs with particle size of 50-100 nm at different concentrations in the range of 1-100 μg / ml, as well as the linear relationship between concentration and characteristic peak intensity, (e) (f) are Raman spectra of PS NPs with particle size of 200-500 nm at different concentrations in the range of 1-100 μg / ml, as well as the linear relationship between concentration and characteristic peak intensity;

[0040] Figure 14 Demonstration diagram of the contact behavior between PS NPs with different particle sizes and Zr-PyDC@Au-Ag / GNS;

[0041] Figure 15 These are the experimental results for evaluating the detection method of this application, where (a) is the uniformity experimental result, (b) is the reproducibility experimental result, and (c) is the high-salt environment simulation test result. DETAILED DESCRIPTION

[0042] 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.

[0043] 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.

[0044] 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.

[0045] Chemicals and Materials

[0046] Zirconium tetrachloride (ZrCl4, analytical grade), 2,5-pyridine dicarboxylate (analytical grade), glacial acetic acid (analytical grade), N,N-dimethylformamide (DMF, analytical grade), anhydrous ethanol (CH3CH2OH, analytical grade), silver nitrate (AgNO3, analytical grade), sodium borohydride (NaBH4, analytical grade), tetrachloroauric acid trihydrate (HAuCl4·3H2O, analytical grade), graphene nanosheets (GNS, 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), polyvinylpyrrolidone (PVP, average molecular weight 58,000), and ethylene glycol (analytical grade).

[0047] Example 1 Synthesis of Zr-PyDC@Au-Ag / GNS

[0048] Reference Figure 1 The Zr-PyDC@Au-Ag / GNS of the present invention is synthesized by the following steps:

[0049] Synthesis of S1 Zr-PyDC

[0050] Dissolve 116.5 mg of zirconium chloride in 5 mL of DMF and sonicate until it is completely dissolved. Then add 5 mL of concentrated hydrochloric acid and cover the lid. Let it stand in the dark for 1 h. Then add 83.5 mg of pyridine-2,5-dicarboxylic acid to the above solution and sonicate until it is completely dissolved. Then transfer the solution to a 20 mL reactor and react at 120°C for 20 h. After the reaction is completed, centrifuge the precipitate, wash it twice with DMF and ethanol each, and then vacuum dry it at 50°C for use.

[0051] S2 Synthesis of Zr-PyDC@Au and Zr-PyDC@Au-Ag

[0052] 10 mg of Zr-PyDC was added to 3 mL of ethanol and sonicated for 20 minutes. Then, 20 μL of a 200 mg / mL chloroauric acid solution was added with stirring. Stirring was continued for at least 5 hours, followed by centrifugation and redissolution of the precipitate in 3 mL of ethanol. Subsequently, 200 μL of a 0.1 M NaBH₄ solution was slowly added dropwise with vigorous stirring. The mixture was allowed to react for 40 minutes, centrifuged, and washed three times with DMF. The Zr-PyDC@Au dispersion was then dispersed in DMF for later use. The 40 mL of the dispersed Zr-PyDC@Au solution was transferred to a 100 mL reactor, followed by the addition of 20 mg of silver nitrate. After complete dissolution by sonication, the mixture was reacted at 120°C for 3 hours. After completion of the reaction, the precipitate was centrifuged and washed three times with DMF to obtain Zr-PyDC@Au-Ag.

[0053] S3 Synthesis of Zr-PyDC@Au-Ag / GNS

[0054] Take an appropriate amount of graphene nanosheets GNS and disperse it in DMF. Stir it with the prepared Zr-PyDC@Au-Ag at a mass ratio of 1:4 at 60°C for 1 h. Centrifuge the precipitate, wash it three times with ethanol, and wash it twice with deionized water. The obtained Zr-PyDC@Au-Ag / GNS is prepared into an appropriate mass concentration for stand-alone use.

[0055] Examples 2-5

[0056] The difference from Example 1 is that in step S2, the amount of silver nitrate added is different, namely 0 mg, 10 mg, 30 mg, and 40 mg, and the rest are the same.

[0057] Comparative Example 1

[0058] Referring to step S1 of Example 1, Zr-PyDC was prepared.

[0059] Comparative Example 2

[0060] Referring to step S2 of Example 1, Zr-PyDC@Au was prepared.

[0061] Comparative Example 3

[0062] Referring to step S2 of Example 1, Zr-PyDC@Au-Ag was prepared.

[0063] Comparative Example 4

[0064] 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.

[0065] Comparative Example 5

[0066] 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.

[0067] Performance testing and characterization

[0068] 1. Material Characterization

[0069] 1. XRD analysis

[0070] As shown in Figure 2a, it can be seen that the Zr-PyDC synthesized in Example 1 has the same skeleton structure as UIO-66, and the loss of crystallinity is small. The five diffraction peaks of Zr-PyDC@Au at 2θ=38.3°, 44.5°, 64.7° and 77.7° correspond to the (111), (200), (220) and (311) lattice planes of Au (JCPDS card number 04-0784); 26.14° and 54.28° belong to the peaks of graphene nanosheets. Figure 2bAs shown in the figure, since the content of Ag NPs is much higher than that of Au NPs, it is speculated that the diffraction peak of Ag covers the characteristic peak of Zr-PyDC and also covers the diffraction peak position of Au, resulting in overlap. Therefore, the five diffraction peaks at 2θ = 38.2°, 44.4°, 64.6° and 77.5° are attributed to the (111), (200), (220) and (311) lattice planes of Ag (JCPDS card number 87-0597), confirming the successful loading of Ag NPs and Au NPs. At the same time, the characteristic peaks of GNS can be seen in Zr-PyDC@Au-Ag / GNS, confirming the successful composite of Zr-PyDC@Au-Ag and GNS.

[0071] 2. TEM analysis

[0072] TEM images ( Figure 3 Figures (a) and (b) show the octahedral cubic structure of Zr-PyDC in Zr-PyDC@Au. A large number of Au NPs, approximately 10 nm in size, are observed covering the Zr-PyDC surface, forming a relatively dense Au NP layer. Figures (c) and (d) show the average size of Ag NPs on the Zr-PyDC@Au-Ag surface, approximately 60 nm in size, covering the Zr-PyDC@Au surface. The Au and Ag NPs are dispersed on the Zr-PyDC surface, forming a bimetallic hybrid SERS substrate with a synergistic enhancement effect. Figure 3 eh in shows the elemental distribution of the main elements (Zr, Ag, Au and C) of Zr-PyDC@Au-Ag, indicating that Au and Ag elements are uniformly distributed on the surface of Zr-PyDC, and at the same time proving the successful synthesis of Zr-PyDC@Au-Ag.

[0073] 3. UV-visible absorption spectrum

[0074] Zr-PyDC, Zr-PyDC@Au, and Zr-PyDC@Au-Ag were further tested using UV-visible spectroscopy. Figure 4 above confirms the successful loading of the precious metal nanoparticles, with the characteristic absorption peak of Au NPs appearing near 535 nm, demonstrating the successful synthesis of the Au NPs. However, due to the subsequent surface formation of Ag NPs, the theoretical characteristic peak at 446 nm overlaps with the characteristic peak of Au NPs due to spectral absorption, resulting in an upward trend in the overall absorption peak, indirectly confirming the successful loading of the Au and Ag NPs.

[0075] 4. XPS analysis

[0076] To further demonstrate the successful loading of gold and silver nanoparticles, XPS analysis was performed on the Zr-PyDC@Au-Ag powder sample. The charge was corrected based on the binding energy of contaminated carbon at 284.8 eV. As shown in Figure 5(a), the presence of elements such as C, N, O, Ag, and Au is indicated. As shown in Figure 5(b)(c), Au 4f has two peaks at 84.87 eV and 88.57 eV, with a peak spacing of 3.70 eV. These peaks are the Au 4f peaks of metallic Au. 7 / 2 and Au 4f 5 / 2 Ag 3d has double peaks at 368.97 eV and 374.97 eV, with a peak spacing of 6.0 eV. These peaks are Ag 3d 5 / 2 and Ag 3d 3 / 2 The above results prove that Ag NPs and Au NPs are successfully modified on the surface of Zr-PyDC.

[0077] 5. Nitrogen adsorption and desorption characterization

[0078] Figure 6 shows the nitrogen adsorption / desorption curve and pore size distribution of Zr-PyDC. The figure shows that the nitrogen adsorption isotherm of Zr-PyDC is a typical type I isotherm, typical of microporous materials. The peak distribution of Zr-PyDC in the Barrett-Joyner-Halenda (BJH) results shows that the pore size range of Zr-PyDC is 1-2 nm, with an average pore size of 1.67 nm, proving that the synthesized Zr-PyDC has a microporous structure. The total surface area of ​​the MOF is 1312.9 m 2 / g, and the total pore volume is 0.5487 cm 3 / g, and this unique morphology provides ample loading space for the loading of precious metal nanoparticles.

[0079] 6. Thermogravimetric analysis

[0080] The TG curves are shown in Figure 7. The mass loss trends of Zr-PyDC, Zr-PyDC@Au, Zr-PyDC@Au-Ag and Zr-PyDC@Au-Ag / GNS are roughly the same. The overall process gradually transitions between the solvation, desolvation and demethylation steps. Due to the composite of noble metal nanogold, noble metal nanosilver and graphene nanosheets, it can be seen that Zr-PyDC has the highest loss rate. The loss rate decreases due to the addition of noble metals. Later, due to the poor heat resistance of graphene nanosheets, the loss rate of Zr-PyDC@Au-Ag / GNS is higher than that of Zr-PyDC@Au-Ag, which confirms the successful composite of the materials.

[0081] 2. Comparison of PS NPs detection effects

[0082] 1. PS NP S Characteristic peak determination

[0083] Sample Preparation: The Zr-PyDC@Au-Ag / GNS 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.

[0084] Normal Raman and SERS spectra were obtained by confocal laser microscope Raman spectrometer (Horiba LabRAM HR Evolution) and 564 nm (3.5%) laser. During the Raman spectrum acquisition, a 50x objective lens was selected and the acquisition wavelength range was 400–1700 cm -1 There are 3 accumulations in 5s acquisition time.

[0085] 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.

[0086] In addition, it can be seen that 1000 cm -1and 1030 cm -1 All substrates with no signals nearby can exclude the interference of SERS substrates on PS NPs detection.

[0087] Secondly, by Figure 8 As shown in b, for the same mass concentration of PS NPs, the SERS composite substrate can also detect the concentration of 10 -2 In summary, the SERS substrates prepared by the present invention are capable of detecting PS NPs with a particle size of 50-100 nm and 20 nm.

[0088] Plastics in the real world exhibit varying particle size distributions, making the study of PS NPs with a wide distribution more innovative and representative. Therefore, dynamic light scattering (DLS) experiments were conducted on PS NPs with a wide size distribution, demonstrating that the PS NPs' size distribution ranged primarily from 200 to 500 nm. Furthermore, due to their small nanoscale size, they can enter the hotspot gaps of the SERS composite material, undergoing inter-plastic attraction and deposition. Furthermore, since the conventional Raman characterization signals of 50-100 nm and 20 nm PS are smaller than those of 200-500 nm PS, subsequent experiments selected 200-500 nm PS for detection, as they offer a more advantageous SERS signal.

[0089] 2. Comparison of test results of materials synthesized in Examples 1-5

[0090] The SERS performance of the SERS substrates synthesized with different amounts of silver nitrate in Examples 1-5 was measured using 200-500 nm PS NPs at a concentration of 0.01 mg / mL. Figure 9 depicts the increase in the amount of silver nitrate. -1 The SERS intensity of the PS at the Zr-PyDC@Au-Ag / GNS substrate changes significantly. This may be attributed to the low content of Ag nanoparticles in the Zr-PyDC@Au-Ag / GNS, which fails to provide sufficient three-dimensional hotspots for the PS nanoparticles. When the silver nitrate dosage is 10 mg, the overly dense coverage of the silver nanoparticles may reduce the coordination between the Ag NPs and the Au NPs, thereby affecting the SERS signal. These results indicate that loading an appropriate amount of Ag NPs onto the Zr-PyDC@Au substrate can significantly improve the performance of the SERS composite substrate.

[0091] 3. Comparison of the test results of each sample in Example 1 and Comparative Examples 1-5

[0092] Using 10 μg / mL and 1 μg / mL PS NPs as probe molecules, SERS tests were performed on the samples in Example 1 and Comparative Examples 1-5, respectively.

[0093] As shown in Figure 10, Zr-PyDC and graphene nanosheets (G) were unable to enhance the SERS signal due to their non-plasmonic structures, thus failing to detect PS NPs. Au and Ag NPs, as plasmonic materials, adsorbed onto the PS NP surface through hydrophobic / electrostatic interactions, resulting in SERS enhancement. However, due to the inherently weak signal characteristics of PS NPs, only a faint characteristic peak could be detected at a concentration of 10 μg / mL. Thanks to the octahedral structure and high specific surface area of ​​Zr-PyDC, the Zr-PyDC@Au substrate constructed in this embodiment of the present invention formed a three-dimensional structure with abundant plasmonic nanogaps, successfully detecting PS NPs at a concentration of 10 μg / mL. Further introduction of Ag NPs to form a Zr-PyDC@Au-Ag bimetallic structure revealed that the synergistic enhancement effect of Au and Ag successfully extended the detection limit to 1 μg / mL for PS NPs. Considering the potential for fluorescence background interference from Zr-PyDC itself, the introduction of ultrahigh-conductivity GNS effectively quenched the fluorescence background, significantly improving the reliability and accuracy of the detection signal at 1 μg / mL PS NPs. This fact demonstrates that the combination of plasma and high-conductivity materials provides the optimal experimental conditions for maximizing the performance of SERS substrates, highlighting the synergistic effect of the two.

[0094] Example 6: Optimization of KI dosage in the detection method

[0095] In this example, the Zr-PyDC@Au-Ag / GNS prepared in Example 1 was mixed with PS NPs. A 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 added dropwise to a 5×5 mm silicon wafer using a glass micropipette and dried in a 50°C oven for 1 hour. The dried sample was then subjected to SERS analysis. The resulting Raman spectra were baseline-corrected.

[0096] The PS NPs had a concentration of 0.01 mg / mL and a particle size distribution of 200-500 nm. The volume ratio of Zr-PyDC@Au-Ag / GNS to PS NPs was fixed at 1:1. In the colloidal solution, the KI concentration increased from 0.01 mol / L to 0.025 mol / L to screen the optimal amount of aggregator KI.

[0097] As shown in Figure 11, 1000 cm -1 The SERS intensity at ΔΨ increased from 736 to 887 as the KI concentration increased from 0.01 mol / L to 0.025 mol / L. This is attributed to the ideal KI level, which forms a strongly bonded monolayer on the SERS substrate surface. However, when the KI concentration exceeds 0.025 mol / L, further increases in concentration lead to a decrease in the SERS intensity. This is due to the excess KI being physically adsorbed outside the strongly bound surface layer, which prevents the access of the nanoplastic and reduces the corresponding SERS signal. Therefore, the optimal KI concentration is 0.025 mol / L for subsequent SERS analysis.

[0098] Example 7: Optimization of substrate concentration in the detection method

[0099] The KI concentration was fixed at 0.025 mol / L. Referring to Example 6, 200-500 nm PS NPs (0.01 mg / mL) were also used as the performance probe, and the Zr-PyDC@Au-Ag / GNS synthesized in Example 1 was used as the SERS substrate. The substrate concentration in the colloidal solution was adjusted to 0.1 mg / mL, 0.25 mg / mL, 0.5 mg / mL, 0.75 mg / mL, and 1 mg / mL for Raman detection.

[0100] like Figure 12 It can be seen that at 1000 cm -1 The SERS intensity at 0.5 mg / mL increased dramatically with increasing substrate concentration, from 321 at 0.1 mg / mL to 930 at 0.5 mg / mL. However, further increases in mass resulted in decreased intensity. Therefore, the optimal response was observed at 0.5 mg / mL. This can be attributed to the generation of a small number of hotspot signals at low substrate volumes. Consequently, the SERS intensity was relatively low. However, when the substrate volume was too large, it was possible that some PS NPs were covered by the SERS substrate. This inevitably resulted in the loss of SERS signals from these particular nanoplastics. Therefore, a SERS substrate concentration of 0.5 mg / mL was selected for subsequent experiments.

[0101] Example 8. Quantitative Detection of PS NPs

[0102] The optimal conditions determined above were used to detect PS NPs with different concentrations, and a quantitative detection method was established.

[0103] Select 1000 cm-1 The Raman peak at 30 nm was taken as the characteristic peak of PS. A 25 mg / mL PS NPs suspension (20 nm, 50-100 nm, 200-500 nm) was diluted to prepare a series of PS standard solutions of 100 μg / mL, 50 μg / mL, 25 μg / mL, 10 μg / mL, and 1 μg / mL. The detection data were obtained and the detection standard curve of PSNPs was drawn based on the peak height intensity. The results are shown in Figure 2. Figure 13 As shown in Figure 2, it can be seen that with the increase of PS suspension concentration, the SERS intensity increases significantly, and its detection limit is 10 -3 mg / mL. The relationship curve between the characteristic peak intensity I and PS concentration was drawn based on the Raman spectrum intensity of the characteristic peak. The linear concentration range was 10 -3 -10 -1 mg / mL, 1000 cm -1 The SERS intensity showed a good linear relationship with the mass concentration (the linear fitting equation of 20 nm PS NPs was y = 19.96x + 532.03, R 2 =0.957, Figure 13b; 50-100 nm PS NPs linear fitting equation y = 12.82x + 711.31, R 2 =0.951; 200-500 nm PS NPs linear fitting equation y = 15.03x + 702.04, R 2 =0.987; y = characteristic peak intensity, x = concentration of PS NPs).

[0104] The above results demonstrate that the Zr-PyDC@Au-Ag / GNS composite substrate prepared in this embodiment of the present invention possesses the following advantageous features (as shown in Figure 14): First, its unique chemical hierarchical structure creates an extended Raman hotspot region in three-dimensional space, significantly extending the effective range of electromagnetic field enhancement compared to traditional substrates. Second, the excellent monodispersity of the substrate material forms a rich nanoscale pore network. This multi-level structure not only effectively suppresses nanoplastic agglomeration but also adapts to PS NPs of varying particle sizes (20-500 nm) through a size-matching effect, ensuring efficient embedding of the nanoplastic particles into the substrate pores. During this process, the PS NPs simultaneously establish multiple contacts with the Zr-PyDC@Au-Ag coordination layer and the GNS surface, forming a uniform "sandwich" enhanced interface. Finally, surface modification with KI further enhances the binding energy between the PSNPs and the substrate, forming a denser plasmonic coupling system. Results demonstrated that the composite substrate successfully achieved highly sensitive detection of PS NPs with three size gradients: 20 nm, 50-100 nm, and 200-500 nm, with minimum detection limits reaching 1 μg / mL. This interface optimization strategy, based on multiscale structural regulation, provides a new technical path for trace detection of nanoplastics in complex systems.

[0105] In summary, the detection method established using the substrate of the embodiment of the present invention has the advantages of high sensitivity and wide detection limit.

[0106] Example 9 Evaluation of the uniformity, reproducibility and anti-interference performance of the detection method

[0107] The anti-interference and uniformity, reproducibility and anti-interference of the detection were evaluated using PS standard solution.

[0108] (1) Uniformity and reproducibility: 0.025 mg / mL 200-500 nm PS NPs were selected for study, and SERS spectra were collected at 15 randomly selected locations on the wafer. As shown in Figure 15a, we analyzed the 1000 cm -1The response intensities of the characteristic peaks at the 30 nm CMOS were measured and found to be between 1035 and 1471. The average intensity was 1231 and the relative standard deviation (RSD) was 9.44%. Under the same experimental conditions, further repeatability tests were performed to improve the reliability of the test results. As shown in Figure 15b, the experiment was carried out in parallel with the five groups of experiments, and three points were randomly selected on each final test sample obtained in each group of experiments for Raman spectroscopy analysis. The Raman spectral data of each point were collected, and the average relative standard deviation (RSD) of the characteristic peak intensity at each point was about 6.97%. The results show that the prepared SERS substrate has good stability.

[0109] (2) 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 NPs (200-500 nm, 10 − 2 mg / mL) signal.

[0110] The results are as follows Figure 15 As shown in c, 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, with an average RSD of about 5.98%.

[0111] Example 10 Application of Zr-PyDC@Au-Ag / GNS in PS NPs detection in actual water samples

[0112] PS NPs (200-500 nm) were spiked into lake water (collected from the Pearl River Lake during the summer) at varying concentrations. The samples were allowed to stand overnight, and the supernatant was collected and used directly without further processing. Since no SERS signal was present in the initial water sample, spike recovery experiments were performed using Pearl River water as the matrix.

[0113] The testing method is as follows: First, a certain volume of Pearl River water is allowed to stand overnight, and the supernatant is collected for later use. A certain volume of PS solution is then measured and prepared to 100 μg / mL, 10 μg / mL, 2 μg / mL, 1 μg / mL, and 0.5 μg / mL. Equal volumes are then added to the Zr-PyDC@Au-Ag / GNS solution. 20 μL of 0.025 M KI is then added, shaken, and allowed to incubate for 1 hour. After the incubation period, 20 μL of the solution is dripped onto a silicon wafer, dried at 50°C for 30 minutes, and then subjected to SERS analysis.

[0114] There was no SERS signal response in the initial water sample, so the recovery of PS NPs was tested by spike addition, 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%.

[0115] Table 1. Results of spiked recovery experiments on actual environmental water samples

[0116]

[0117] These results confirm the feasibility of the detection method of the present invention in real aquatic environment detection.

[0118] In summary, the present invention utilizes the high porosity, adjustable pore size and ultra-large specific surface area characteristics of the organic metal framework to successfully load precious metal nanoparticles onto the surface of Zr-PyDC and composite them onto graphene nanosheets through electrostatic attraction. Because Zr-PyDC itself is also a product with metal as a node, it can, to a certain extent, synergize with plasma, breaking through the sensitivity bottleneck of traditional SERS substrates. Similarly, graphene nanosheets, due to their own ultra-high order and high electronic conductivity, have an excellent synergistic enhancement effect on the construction of SERS substrates. The SERS substrate constructed by the present invention achieves quantitative detection of 100 μg / mL - 1 μg / mL PS NPs in water environment. The relative deviation (RSD) of the test results of the same batch and different batches of SERS substrate materials prepared is less than 10%, which meets the quantitative detection requirements. In actual water body detection, the corresponding quantitative curve can be selected according to the characteristics of the target object and the characteristics of the environment in which it is located to achieve the goal of accurate quantification. This study constructed a composite substrate of Zr-PyDC loaded with precious metal nanoparticles, which resulted in more reliable and stable detection results, and an order of magnitude higher sensitivity than previous studies. This provides a new strategy for the efficient detection of PS NPs, has great application potential, and broadens the research boundaries of SERS technology in the analysis of environmental pollutants.

[0119] 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 constructing a Zr-PyDC@Au-Ag / GNS composite SERS substrate, characterized in that: Including steps: S1 Synthesis of Zr-PyDC, Dissolve zirconium chloride in DMF, then add concentrated hydrochloric acid, seal and stand in the dark for 0.5-2 hours, then add pyridine-2,5-dicarboxylic acid to the resulting solution and disperse until it is completely dissolved, then transfer the solution to a reactor and react at 110-130° C. for 15-25 hours. After the reaction is completed, centrifuge to obtain a precipitate, wash, and dry to obtain the Zr-PyDC; S2 Synthesis of Zr-PyDC@Au-Ag, A chloroauric acid solution was added to an ethanol solution of Zr-PyDC under stirring, and the mixture was stirred for more than 5 hours. The precipitate was then centrifuged and redissolved in ethanol. A NaBH4 solution was then added dropwise under vigorous stirring. After the reaction, the mixture was centrifuged and washed to obtain Zr-PyDC@Au. The Zr-PyDC@Au was then dispersed in DMF, and silver nitrate was added to completely dissolve the mixture. The mixture was reacted at 110-130°C for 2-5 hours. After the reaction, the precipitate was centrifuged and washed to obtain Zr-PyDC@Au-Ag. S3 Synthesis of Zr-PyDC@Au-Ag / GNS; The graphene nanosheets GNS and the Zr-PyDC@Au-Ag obtained in step S2 were dispersed in DMF, stirred at 60° C., centrifuged to obtain a precipitate, and washed to obtain the Zr-PyDC@Au-Ag / GNS composite SERS substrate.

2. The method for constructing the Zr-PyDC@Au-Ag / GNS composite SERS substrate according to claim 1, characterized in that: In step S1, zirconium chloride: DMF: concentrated hydrochloric acid: pyridine-2,5-dicarboxylic acid = 115-118 mg: 3-8 mL: 3-8 mL: 82-85 mg.

3. The method for constructing the Zr-PyDC@Au-Ag / GNS composite SERS substrate according to claim 1, characterized in that: In the step S2, The concentration of Zr-PyDC ethanol solution is 3-4 mg / mL, the concentration of chloroauric acid solution is 180-220 mg / mL, and the concentration of NaBH4 solution is 0.05-0.2 mol / L. According to the volume ratio, Zr-PyDC ethanol solution: chloroauric acid solution: NaBH4 solution = 3:0.02:0.2; According to the mass ratio, Zr-PyDC: silver nitrate = 10:0.1~40.

4. The method for constructing the Zr-PyDC@Au-Ag / GNS composite SERS substrate according to claim 1, characterized in that: In the step S3, According to the mass ratio, graphene nanosheets GNS: Zr-PyDC@Au-Ag = 1:

4.

5. The composite SERS substrate prepared by the construction method according to any one of claims 1 to 4.

6. A method for detecting nanoplastics based on the composite SERS substrate according to claim 5, characterized in that: The steps include: A Zr-PyDC@Au-Ag / GNS solution was prepared and then mixed with a polystyrene nanoparticle suspension. KI was added as an aggregating agent. The resulting solution was thoroughly mixed and allowed to stand until the sample formed a stable colloidal solution for SERS detection.

7. The nanoplastic detection method according to claim 6, characterized in that: In the colloidal solution, the KI concentration is 0.01-0.025 mol / L.

8. The nanoplastic detection method according to claim 6, characterized in that: The concentration of the Zr-PyDC@Au-Ag / GNS solution is 0.1-1 mg / mL.

9. The nanoplastic detection method according to claim 6, characterized in that: The particle size of the nano plastic is 20-500 nm.

10. The nanoplastic detection method according to any one of claims 6 to 9, characterized in that: The SERS detection includes qualitative detection and / or quantitative detection. The quantitative detection draws a curve of the relationship between the intensity of the characteristic peak and the concentration of the nanoplastic according to the Raman spectrum intensity of the characteristic peak to determine the concentration of the nanoplastic in the sample to be tested.

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