Preparation method and trace detection application of MXene-based novel composite SERS (Surface Enhanced Raman Scattering) substrate

Abstract

The invention discloses a preparation method and trace detection application of a novel composite SERS (Surface Enhanced Raman Scattering) substrate based on MXene, and particularly relates to the technical field of nano material technology and spectrum detection. And performing mediated growth on the synthesized ZnO seed crystal, and loading the ZnO seed crystal on the surface of the MXene nanosheet through electrostatic adsorption by utilizing the Zeta potential difference between the MXene nanosheet and the ZnO seed crystal to obtain the MXene / ZnO composite material. And modifying an Ag (at) Au core-shell structure on the MXene / ZnO composite material to finally obtain the MXene / ZnO (at) Ag (at) Au composite material, namely the composite SERS substrate.

Description

Technical Field

[0001] The present invention relates to the fields of nanomaterial technology and spectral detection technology, and in particular to a preparation method of a novel composite SERS substrate based on MXene and its trace detection application. Background Art

[0002] Surface-enhanced Raman scattering technology has become an important means of trace analysis due to its high sensitivity and fingerprint recognition properties. However, traditional SERS substrates have many limitations. Pure noble metal substrates (such as Au / Ag NPs) are widely used in the preparation of SERS substrates due to their excellent plasmonic properties, but they are costly, have poor uniformity, and low molecular adsorption selectivity. Bimetallic nanomaterials are composed of two different metals and have more advantages than single metal nanomaterials in SERS applications. Perhaps the Ag@Au bimetallic structure cannot achieve the enhancement effect of a single metal silver nanostructure of the same size, but compared with the noble metal gold nanostructure, their signal enhancement ability is better. Compared with noble metal nanomaterials, traditional semiconductor substrates have higher flexibility and selective enhancement properties, but their enhancement factor (EF) effect is generally lower. Some two-dimensional materials have also been shown to have Raman signal enhancement properties. Studies have shown that MXene materials have good chemical selectivity and certain plasmonic properties in SERS applications. Although they have high conductivity and rich surface functional groups (-O, -F, etc.), their SERS activity is insufficient when used alone. The synergistic effect of electromagnetic enhancement and chemical enhancement can give this type of material an excellent enhancement factor.

[0003] Existing MXene composite substrates are mostly modified with a single metal, which makes it difficult to balance stability and enhancement effects, and fails to solve the problem of balancing precious metal-semiconductor synergistic enhancement and stability. The invention patent application number CN201910149418.1 uses Ag / MXene-Ti3C2 composite to prepare materials with high SERS activity, but fails to solve the problem of Ag being easily oxidized and unstable. In addition, the "Deposition of hydrophilic Ti3C2T on superhydrophobic Zn0 nanorod arrays" x To improve the surface enhanced Raman scattering performance" (DOI:10.1186 / s12951-022-01756-4) by adding hydrophilic Ti3C2T x A SERS substrate was constructed by depositing it onto a superhydrophobic ZnO nanorod array. While this substrate achieves high sensitivity through analyte concentration and interfacial charge transfer, its signal strength is limited by the weak electromagnetic enhancement properties of ZnO, with the enhancement factor being only 1 / 100 of that of noble metal substrates. This invention addresses this issue by introducing an Ag@Au core-shell structure, while retaining the high adsorption properties of MXene / ZnO, while utilizing the metal LSPR effect to boost the enhancement factor. Summary of the Invention

[0004] To this end, the present invention provides a preparation method of a novel composite SERS substrate based on MXene and its trace detection application. By designing a MXene / ZnO@Ag@Au system, the charge transfer ability of MXene, the exciton resonance effect of ZnO and the bimetallic synergy of Ag@Au are utilized to significantly improve the sensitivity and stability of the substrate, thereby solving the problems raised in the background technology.

[0005] To achieve the above objectives, the present invention provides the following technical solutions: a method for preparing a novel composite SERS substrate based on MXene, wherein the substrate uses a single-layer MXene nanosheet as a carrier; the synthesized ZnO seed crystals are subjected to mediated growth, and the Zeta potential difference between the MXene nanosheets and the ZnO seed crystals is utilized to load the ZnO seed crystals on the surface of the MXene nanosheets by electrostatic adsorption to obtain a MXene / ZnO composite material; and an Ag@Au core-shell structure is modified on the MXene / ZnO composite material to finally obtain a MXene / ZnO@Ag@Au composite material, i.e., a composite SERS substrate.

[0006] Preferably, the single-layer MXene nanosheet is Ti3C2T x , where T x represents a surface functional group, which is at least one of a hydroxyl group -OH, an oxygen anion -O, or a fluorine atom -F.

[0007] Preferably, the particle size of the Ag@Au bimetallic core-shell nanoparticles is 50 nm, and the thickness of the Au shell is 5 nm.

[0008] Preferably, the steps for preparing a single-layer MXene nanosheet include:

[0009] HCl / LiF was used to in situ generate HF etching of the Ti3AlC2MAX phase. 2.4g of LiF was added to a polytetrafluoroethylene beaker and dissolved in 40mL of 9M hydrochloric acid solution. The HCl / LiF mixed etching solution was then magnetically stirred at room temperature for 20 minutes to prepare a HCl / LiF mixed etching solution. Subsequently, 2g of the Ti3AlC2MAX phase material was added to 40mL of the above etching solution and etched at 40°C for 48h. Under nitrogen protection, the monolayer MXene was exfoliated in an ice bath for 1h. The solution was then washed repeatedly with 2M HCl solution and deionized water until the pH of the supernatant was above 6. The solution was centrifuged at 3500rpm for 30 minutes, and the supernatant was collected to obtain dark green monolayer MXene nanosheets. The solution tended to retain large monolayers or few-layer MXene (larger lateral dimensions) while allowing some incompletely exfoliated multilayer structures to precipitate.

[0010] Preferably, the preparation steps of the MXene / ZnO composite material include:

[0011] ZnO nanoparticles were prepared by the seed growth method. Zinc acetate dihydrate (CH3COO)2Zn·2H2O was added to diethylene glycol (DEG) and heated to 160°C in an oil bath under N2 protection. The emulsified colloidal suspension obtained from the reaction was centrifuged at 8000 rpm, and the supernatant was used as ZnO seeds for subsequent reactions. (CH3COO)2Zn·2H2O was dissolved in diethylene glycol (DEG) and heated from room temperature to 140°C in an oil bath. The supernatant ZnO seeds were slowly added dropwise at a rate of 1 drop / min through a separatory funnel, and the temperature was gradually raised to 160°C. The mixture was stirred for 1 hour and cooled to room temperature after the reaction was completed. The product was washed with ethanol to obtain monodisperse ZnO nanoparticles. MXene / ZnO composite materials were formed by self-assembly using electrostatic adsorption between MXene and ZnO.

[0012] Preferably, the zeta potential difference between the MXene nanosheets and the ZnO seed crystals is greater than 50 mV. Surface end group modification: By controlling the reaction conditions during HF / HCl etching of the MAX phase, the MXene surface is enriched with -O / -F end groups, resulting in a zeta potential of approximately -30 mV. Synthesis process optimization: ZnO seed crystals are prepared using a sol-gel method. By adjusting the ratio of zinc acetate to complexing agent, the ZnO surface is positively charged, with a zeta potential of approximately +30 mV.

[0013] Preferably, Ag nanoparticles are deposited on the oxygen vacancies of the MXene / ZnO composite material by reacting NaBH4 with AgNO3 at 70°C for 1 h, and then 6.25×10 -3 M NH2OH·HCl and 4.65×10 -4 M HAuCl4·4H2O was replaced for 45 min to form an Au shell, achieving Au coating on the Ag seed crystal and finally forming an Au@Ag core-shell structure.

[0014] The present invention also discloses an application. The composite SERS substrate prepared by the above method can synergize the electromagnetic field enhancement of noble metals with the chemical enhancement of MXene charge transfer and semiconductor exciton resonance to enhance the Raman signal. The enhancement effect is excellent, and the detection limit of 4-NTP reaches 6.53×10 -13 M, RSD = 1.95%.

[0015] Preferably, the prepared composite SERS substrate is used for rapid detection of trace substances, including traditional Chinese medicine active substances, mycotoxins and pesticide residues.

[0016] The present invention has the following advantages:

[0017] The present invention uses a single-layer MXene nanosheet as a carrier; mediates the growth of synthesized ZnO seeds, utilizes the Zeta potential difference between the MXene nanosheet and the ZnO seeds, and loads the ZnO seeds on the surface of the MXene nanosheet by electrostatic adsorption to obtain a MXene / ZnO composite material; and modifies the MXene / ZnO composite material with an Ag@Au core-shell structure to finally obtain a MXene / ZnO@Ag@Au composite material, i.e., a composite SERS substrate. Compared with the prior art, the preparation method of the present invention is simple to operate, cost-controlled, and can be mass-produced. The prepared MXene / ZnO@Ag@Au composite material can be used as a substrate to enhance the signal of probe molecules, and the enhancement effect is excellent. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Zeta potential diagrams of MXene, ZnO, MXene / ZnO, and MXene / ZnO@Ag@Au provided by the present invention;

[0019] Figure 2 SEM characterization images of MXene, ZnO, MXene / ZnO and MXene / ZnO@Ag@Au provided by the present invention;

[0020] Figure 3 UV images of MXene / ZnO with different ratios provided by the present invention;

[0021] Figure 4 UV images of MXene, ZnO, MXene / ZnO, and MXene / ZnO@Ag@Au provided by the present invention;

[0022] Figure 5 The SERS images of the MXene / ZnO detection probe molecules with different ratios provided by the present invention;

[0023] Figure 6 A comparison chart of the SERS enhancement effects of MXene, ZnO, MXene / ZnO, Ag, Ag@Au, and MXene / ZnO@Ag@Au provided by the present invention when detecting 4-NTP at the same concentration;

[0024] Figure 7 Comparison of the SERS enhancement effects of MXene, ZnO, MXene / ZnO, Ag, Ag@Au, and MXene / ZnO@Ag@Au at the 4-NTP characteristic peak provided by the present invention;

[0025] Figure 8 This is a diagram showing the detection stability of 4-NTP using SERS substrates of different batches of MXene / ZnO@Ag@Au provided by the present invention;

[0026] Figure 9 This is a graph showing the repeatability test of 4-NTP on SERS substrates of different batches of MXene / ZnO@Ag@Au provided by the present invention. DETAILED DESCRIPTION

[0027] The following describes the implementation of the present invention using specific embodiments. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. Obviously, the embodiments described are only a portion of the present invention, not all of it. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention.

[0028] Figure 1 Zeta potential plots for MXene, ZnO, MXene / ZnO, and MXene / ZnO@Ag@Au. The horizontal axis represents the sample type (MXene, ZnO, MXene / ZnO, MXene / ZnO@Ag@Au), and the vertical axis represents the zeta potential (mV), which indicates the surface charge properties of the material. Blue represents the zeta potential of MXene nanosheets, green represents the zeta potential of ZnO nanoparticles, orange represents the zeta potential of MXene / ZnO composites, and red represents the zeta potential of MXene / ZnO@Ag@Au. The zeta potentials of MXene and ZnO have opposite signs (negative for MXene and positive for ZnO), and the potential difference is greater than 50 mV. The potential of MXene / ZnO lies between the two, indicating successful electrostatic adsorption and laying the foundation for subsequent composite substrate preparation. Ag@Au is a noble metal with an inherently negative potential. The potential of the MXene / ZnO@Ag@Au composite grown on MXene / ZnO becomes increasingly negative.

[0029] Figure 2 The following are SEM characterization images of MXene, ZnO, MXene / ZnO, and MXene / ZnO@Ag@Au. MXene monolayer nanosheets exhibit a transparent, wrinkled sheet structure. ZnO nanoparticles are uniformly dispersed spherical particles. MXene / ZnO composite material: ZnO particles are anchored on the surface of the MXene sheet, forming a dense load through electrostatic adsorption, providing a basis for subsequent charge transfer (CM). In the MXene / ZnO@Ag@Au composite material, Ag@Au core-shell particles are uniformly distributed at the MXene / ZnO interface. This structure enhances the SERS performance through a synergistic mechanism of the LSPR effect of Ag@Au (electromagnetic enhancement) and charge transfer at the MXene / ZnO interface (chemical enhancement).

[0030] Figure 3UV spectra of different MXene / ZnO probe molecules and different materials are shown. The horizontal axis is wavelength (nm), and the vertical axis is absorbance (OD) (au). The multiple curves correspond to different MXene:ZnO mass ratios (80:20, 50:50, 20:80, and 10:90) and the UV-Vis spectra of MXene, MXene / ZnO, MXene / ZnO@Ag, and MXene / ZnO@Ag@Au. The optimal MXene:ZnO ratio is 80:20. The absorbance decreases with increasing ZnO ratio, suggesting that excess ZnO may shield MXene active sites. The surface plasmon resonance (SPR) absorption peak of Ag nanoparticles is at 420 nm, and the red shift of the absorption peak indicates the Ag@Au core-shell structure.

[0031] Figure 4 These are the UV images of different materials measured when the optimal ratio of MXene to ZnO is 80:20;

[0032] Figure 5 The SERS images of different ratios of MXene / ZnO detection probe molecules. The horizontal axis is Raman shift (cm -1 ), with the vertical axis representing Raman intensity (au). Multiple curves correspond to SERS images of different MXene:ZnO mass ratios (80:20, 50:50, 20:80, and 10:90).

[0033] Figure 6 The SERS enhancement effect comparison chart for each material with the same concentration of 4-NTP is shown in the figure. The horizontal axis is Raman shift (cm -1 ), the vertical axis is Raman intensity (au). Pure MXene is the baseline signal, ZnO has a weak CM effect, MXene / ZnO is CM-dominated, and MXene / ZnO@Ag@Au composites are EM and CM synergistic. The characteristic peak of 4-NTP is at 1340 cm -1 (NO2 symmetric stretching). MXene / ZnO@Ag@Au at 1340cm -1 The intensity is 10 5 After the introduction of Ag@Au, electromagnetic enhancement (EM) superimposed on chemical enhancement (CM) of MXene / ZnO, the EF reached 10 8 ( Figure 7 verify).

[0034] Figure 7The figure shows the SERS enhancement effect comparison at the characteristic peak of 4-NTP. The horizontal axis is the material type (MXene, ZnO, MXene / ZnO, MXene / ZnO@Ag@Au). The vertical axis is the Raman intensity (au). The histogram of MXene / ZnO@Ag@Au detecting 4-NTP is significantly higher than that of other materials. The stability reaches RSD = 1.95% ( Figure 8 and Figure 9 ), which is much lower than traditional precious metal substrates.

[0035] Comparative Group 1: Patent application number CN201910149418.1 proposes an Ag / MXene-Ti3C2 composite material. This patent uses Ag nanoparticles to modify MXene to prepare a SERS substrate, and uses the localized surface plasmon resonance (LSPR) effect of Ag to enhance the Raman signal. The specific method includes: loading Ag NPs on the MXene surface by chemical reduction to form an Ag / MXene composite material. Tests show that the detection limit of the substrate for the probe molecule (4-NTP) can reach 10 -12 M, the enhancement factor (EF) is better than that of pure MXene. However, it has certain limitations. For example, Ag NPs are easily oxidized to Ag2O in the air, resulting in SERS signal attenuation and poor stability (the signal intensity drops by about 40% after 30 days). Relying only on the electromagnetic enhancement of Ag without combining the chemical enhancement of semiconductor materials limits the further improvement of sensitivity. The present invention solves the Ag oxidation problem by introducing ZnO and Au shells, and at the same time uses the exciton resonance of ZnO and the charge transfer of MXene to achieve multiple enhancements, with a detection limit (10 -14 M) is significantly better than this patent.

[0036] Comparative Group 2: Journal of Nanobiotechnology, "Deposition of Hydrophilic Ti3C2T on Superhydrophobic Zn0 Nanorod Arrays" x To improve the surface enhanced Raman scattering performance, a ZnO / Ti3C2T x Composite materials, hydrophilic Ti3C2T deposited on superhydrophobic ZnO nanorod arrays by hydrothermal method x Nanosheets, constructing ZnO / Ti3C2T x Composite SERS substrate. Its core innovations include: Research shows that ZnO and Ti3C2T x The interfacial charge transfer enhanced the chemical enhancement effect (CM), and the detection limit of R6G was 10 -11M. This substrate has high molecular adsorption selectivity and uniformity, but the signal intensity is weak, far lower than that of precious metal substrates. The pure semiconductor system lacks electromagnetic enhancement (EM), resulting in insufficient SERS signal intensity. This non-patent document does not introduce Ag / Au NPs and cannot utilize the LSPR effect. The present invention introduces an Ag@Au core-shell structure based on ZnO / MXene, combining electromagnetic enhancement (Ag@Au) and chemical enhancement (ZnO / MXene), which improves the enhancement factor and reduces the detection limit by 2 orders of magnitude (10 -14 M).

[0037] Example 1: Adding different masses of ZnO NPs to 2 mg / mL Ti3C2T x MXene colloidal solution.

[0038] Ultrasonic mixing was performed for 60 minutes to obtain mixed suspensions with different ZnO NPs contents, among which Ti3C2T x The mass ratios of MXene to ZnONPs were 80:20, 50:50, 20:80, and 10:90, respectively.

[0039] Take pure Ti3C2T x The MXene solution was mixed by ultrasonication for 60 min and dried at 60 °C for 12 h as a control sample.

[0040] 10 μL of 4-NTP solution was added to each MXene / ZnO composite material.

[0041] Adsorption was allowed to proceed for 12 h in the dark to ensure sufficient loading of 4-NTP.

[0042] Effect: mass ratio Ti3C2T x MXene:ZnO=80:20 is the optimal ratio for detecting 4-NTP. ( Figure 5 )The horizontal axis is the charge Raman shift, and the vertical axis is the Raman signal intensity, reflecting the SERS enhancement effect. Different curves correspond to SERS spectra of different MXene:ZnO mass ratios (pure MXene, 80:20, 50:50, 20:80, 10:90), which are used to optimize the ratio of composite materials. The high conductivity and rich functional groups (-O / -F) of MXene promote charge transfer, and ZnO enhances molecular adsorption. Excess ZnO will shield the active sites of MXene and weaken the CM effect. 80:20 is the optimal ratio, which balances the charge transfer of MXene and the exciton enhancement of ZnO (Example 1). The problem of Ag's easy oxidation and instability is solved. Ag is easily oxidized, resulting in attenuation of the SERS signal. The present invention forms an Au shell through a replacement reaction to prevent oxidation of the Ag core. Under the same conditions, the RSD of MXene / ZnO@Ag@Au is 1.95% ( Figure 8 and Figure 9 ), while the Ag / MXene substrate RSD>10%. At the same time, the problem of insufficient substrate signal intensity was solved. The above-mentioned ZnO / Ti3C2T x The substrate (DOI:10.1186 / s12951-022-01756-4) depends only on CM, with an EF of 1.49×10 7 The present invention introduces LSPR effect (EM) by growing Ag@Au, which increases the peak intensity. MXene / ZnO@Ag@Au has an EF of 10 8 , far exceeding MXene / ZnO and pure Ag@Au(10 6 ) has a synergistic effect.

[0043] Example 2: After mixing MXene and ZnO in a mass ratio of 80:20, 1% AgNO3 and 0.1% NaBH4 were added to react to obtain an Ag NPs-modified MXene / ZnO composite material.

[0044] Add 6.25×10 -3 M NH2OH·HCl and 4.65×10 -4 M HAuCl4·4H2O (about 2 mL / min), stirred for 45 min in a dark environment, centrifuged, and washed with deionized water.

[0045] Add 10 μL of 4-NTP solution to the MXene / ZnO@Ag@Au composite.

[0046] Adsorption was allowed to proceed for 12 h in the dark to ensure sufficient loading of 4-NTP.

[0047] Effect: The SERS signal of 4-NTP was significantly enhanced under 785nm laser, with RSD = 1.95%. (Figure Figure 8 and Figure 9 ); Figure 8 and Figure 9 The detection stability and repeatability of 4-NTP using MXene / ZnO@Ag@Au as SERS substrates are tested. The horizontal axis represents the test batch and the vertical axis represents the Raman signal intensity. The results show that the signal intensity fluctuation is very small, with the difference between batches less than 5% (RSD = 1.95%). The horizontal axis represents the Raman shift (cm -1 ), with the vertical axis representing Raman intensity (au). Even after long-term storage, the signal shows no significant attenuation, demonstrating that the Au shell effectively prevents Ag oxidation.

[0048] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made thereto. Therefore, such modifications and improvements, without departing from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. A method for preparing a novel composite SERS substrate based on MXene, characterized by: The substrate uses a single-layer MXene nanosheet as a carrier; the synthesized ZnO seeds are mediated to grow, and the Zeta potential difference between the MXene nanosheet and the ZnO seeds is utilized to load the ZnO seeds on the surface of the MXene nanosheet through electrostatic adsorption to obtain a MXene / ZnO composite material; the Ag@Au core-shell structure is modified on the MXene / ZnO composite material to finally obtain a MXene / ZnO@Ag@Au composite material, i.e., a composite SERS substrate.

2. The method for preparing a novel composite SERS substrate based on MXene according to claim 1, characterized in that: The single-layer MXene nanosheet is Ti3C2T x , where T x represents a surface functional group, which is at least one of a hydroxyl group -OH, an oxygen anion -O, or a fluorine atom -F.

3. The method for preparing a novel composite SERS substrate based on MXene according to claim 1, characterized in that: The particle size of the MXene / ZnO@Ag@Au is 150 nm.

4. The method for preparing a novel composite SERS substrate based on MXene according to claim 1, characterized in that: The steps for preparing single-layer MXene nanosheets include: HCl / LiF was used to in situ generate HF to etch the Ti3AlC2MAX phase. 2.4g of LiF was added to a polytetrafluoroethylene beaker and dissolved in 40mL of 9M hydrochloric acid solution. The HCl / LiF mixed etching solution was then magnetically stirred at room temperature for 20 minutes to prepare. Subsequently, 2g of the Ti3AlC2MAX phase material was added to 40mL of the above-mentioned etching solution and etched at 40°C for 48h. Under nitrogen protection, the monolayer MXene was exfoliated in an ice bath for 1h. The monolayer was washed repeatedly with 2M HCl solution and deionized water until the pH of the supernatant was above 6. The supernatant was centrifuged at 3500rpm for 30 minutes, and the upper liquid was collected to obtain dark green monolayer MXene nanosheets.

5. The method for preparing a novel composite SERS substrate based on MXene according to claim 1, characterized in that: The preparation steps of MXene / ZnO composite materials include: ZnO nanoparticles were prepared by the seed growth method. Zinc acetate dihydrate (CH3COO)2Zn·2H2O was added to diethylene glycol (DEG) and heated to 160°C in an oil bath under N2 protection. The emulsified colloidal suspension obtained from the reaction was centrifuged at 8000 rpm, and the supernatant was used as ZnO seeds for subsequent reactions. (CH3COO)2Zn·2H2O was dissolved in diethylene glycol (DEG) and heated from room temperature to 140°C in an oil bath. The supernatant ZnO seeds were slowly added dropwise at a rate of 1 drop / min through a separatory funnel, and the temperature was gradually raised to 160°C. The mixture was stirred for 1 hour and cooled to room temperature after the reaction was completed. The product was washed with ethanol to obtain monodisperse ZnO nanoparticles. MXene / ZnO composite materials were formed by self-assembly using electrostatic adsorption between MXene and ZnO.

6. The method for preparing a novel composite SERS substrate based on MXene according to claim 5, characterized in that: The zeta potential difference between MXene nanosheets and ZnO seeds is greater than 50 mV.

7. The method for preparing a novel composite SERS substrate based on MXene according to claim 1, characterized in that: Ag nanoparticles were deposited on the oxygen vacancies of MXene / ZnO composites by reacting NaBH4 with AgNO3 at 70 °C for 1 h, and then 6.25×10 -3 M NH2OH·HCl and 4.65×10 -4 MHAuCl4·4H2O replacement was performed for 45 min to form an Au shell, achieving Au coating on the Ag seed crystal and ultimately forming an Au@Ag core-shell structure.

8. An application, characterized in that: The composite SERS substrate prepared by the method according to any one of claims 1 to 7 can synergize the electromagnetic field enhancement of noble metals with the chemical enhancement of MXene charge transfer and semiconductor exciton resonance to enhance the Raman signal, and the detection limit of 4-NTP is 6.53×10 -13 M, RSD = 1.95%.

9. The use according to claim 8, characterized in that: The prepared composite SERS substrate is used for the rapid detection of trace substances, including traditional Chinese medicine active substances, mycotoxins and pesticide residues.

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