Flexible SERS (Surface Enhanced Raman Scattering) substrate for detecting thiophanate-methyl as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of pesticide residue detection, and particularly relates to a flexible SERS (Surface Enhanced Raman Scattering) substrate for detecting thiophanate-methyl as well as a preparation method and application of the flexible SERS substrate. The flexible SERS substrate is constructed by depositing an MXene nanosheet on the surface of a carbon paper fiber in situ and then electrochemically depositing Au nanoparticles. According to the substrate, the local surface plasmon resonance effect of the Au nanoparticles and the synergistic enhancement effect of high conductivity and large specific surface area of the MXene material are fully utilized, and the strength of Raman signals is remarkably improved. Meanwhile, due to the specific interaction between the functional group on the surface of the MXene and the TPM molecules, the substrate is endowed with high-selectivity recognition capability on the TPM. The prepared flexible SERS substrate has the advantages of being easy and convenient to prepare, low in cost, high in sensitivity, good in reproducibility, good in stability and the like, and can be used for on-site rapid and quantitative detection of TPM pesticide residues in agricultural products such as fruits and the like.

Description

Technical Field

[0001] This invention belongs to the field of thiophanate-methyl detection technology, specifically relating to a flexible SERS substrate for detecting thiophanate-methyl, its preparation method, and its application. Background Technology

[0002] Thiophanate-methyl, abbreviated as TPM, is widely used in global agricultural plant protection systems due to its high efficiency, broad spectrum and low toxicity. In actual agricultural production, it can effectively combat a variety of fungal diseases of vegetables, fruits, grain crops, cash crops and ornamental plants, especially effective in controlling diseases such as powdery mildew and rust.

[0003] However, the persistence of TPMs in the environment and the potential health hazards they may pose are significant concerns. Both domestic and international regulations have established strict maximum residue limits (MRLs) for TPMs in fruits and other foods. For example, GB 2763-2021 sets the limit at 5 mg / kg for citrus fruits, apples, and kiwis; 3 mg / kg for pears and grapes; and 2 mg / kg for tropical and melon fruits such as mangoes, bananas, and watermelons. The EU standard is 6 mg / kg. Therefore, the detection and control of TPM residues are crucial for ensuring the safety of fruits, vegetables, and other foods.

[0004] Currently, conventional methods for TPM analysis include gas chromatography, high-performance liquid chromatography, mass spectrometry, and capillary electrophoresis. However, these methods generally suffer from drawbacks such as high instrument costs and time-consuming operation, making it difficult to meet the needs of rapid on-site detection. Therefore, developing an efficient and portable method for rapid on-site detection of TPM is of significant practical importance.

[0005] Surface-enhanced Raman spectroscopy, or SERS for short, has shown great potential in the field of trace substance detection due to its advantages such as high sensitivity, fingerprint recognition capabilities, and rapid non-destructive testing. The core of SERS technology lies in its substrate, whose performance directly determines the sensitivity, reproducibility, and practicality of the detection. Existing SERS substrates are mainly divided into two categories: rigid SERS substrates and flexible SERS substrates. Rigid SERS substrates are typically constructed by depositing metal nanoparticles on the surface of hard materials such as glass and silicon wafers using physical or chemical methods. While these substrates offer significant enhancement effects, their fabrication processes are usually complex and costly. Furthermore, their brittle mechanical properties prevent them from bending or adhering to irregular sample surfaces, resulting in low sampling efficiency and unstable signal acquisition, making them unsuitable for on-site wiping sampling. Flexible SERS substrates, on the other hand, use polymer films, filter paper, or ordinary textile fibers as substrates and are prepared by loading metal nanoparticles through physical adsorption or chemical modification, thus solving the adhesion problem of rigid substrates. However, the bonding force between metal nanoparticles and flexible substrates is weak, and they are prone to detachment, resulting in poor signal uniformity and reproducibility, as well as weak anti-interference ability in complex matrices. Summary of the Invention

[0006] To address the technical problems of weak bonding between metal nanoparticles and flexible substrates in existing SERS substrates, which leads to poor signal uniformity and reproducibility, as well as weak anti-interference ability in complex matrices, this invention provides a flexible SERS substrate that is easy to prepare, low in cost, and has excellent performance, along with its preparation method and applications.

[0007] This invention achieves a flexible SERS substrate by in-situ growth of MXene nanosheets on a flexible substrate, followed by uniform loading of gold nanoparticles onto the MXene nanosheets, with nano-gap formations between adjacent gold nanoparticles creating uniformly distributed nano-gap "hot spots." The in-situ growth of MXene nanosheets and their strong bonding with the flexible substrate, along with the uniform loading of Au nanoparticles on the MXene surface, result in a tight bond between the three. Simultaneously, the LSPR effect of Au nanoparticles and the synergistic enhancement effect of the high conductivity and large specific surface area of ​​MXene significantly enhance the Raman signal intensity of thiophanate-methyl. Furthermore, the specific interaction between the functional groups on the MXene surface and TPM molecules endows the substrate with high selective recognition capability for TPMs, thereby achieving highly sensitive and selective detection of thiophanate-methyl in fruit samples.

[0008] This flexible sensor is simple to prepare and low in cost, providing a new and effective method for rapid on-site detection of thiophanate-methyl pesticide residues in agricultural products, thereby ensuring the safety of fruits and food and meeting practical testing needs.

[0009] The first objective of this invention is to provide a flexible SERS substrate for detecting thiophanate-methyl, the flexible SERS substrate being composed of a flexible substrate, MXene nanosheets grown in situ on the surface of the flexible substrate, and gold nanoparticles loaded on the MXene nanosheets; and nano gaps are formed between adjacent gold nanoparticles.

[0010] Preferably, the gold nanoparticles have a uniform size distribution, with gaps of 1 to 3 nanometers between adjacent gold nanoparticles; this significantly enhances the local electromagnetic field, thereby improving SERS performance.

[0011] Preferably, the MXene nanosheets are Ti3C2T x Nanosheets; where x is 1.8 to 2.2.

[0012] Preferably, the flexible substrate is carbon paper. Carbon paper is characterized by its stability, acid and alkali resistance, low cost, and environmental friendliness.

[0013] A second objective of this invention is to provide a method for preparing a flexible SERS substrate for detecting thiophanate-methyl, comprising the following steps: MXene nanosheets were deposited in situ on the surface of a flexible substrate to form a continuous conductive network structure, resulting in CP-MXene. CP-MXene was then electrochemically deposited in a mixed solution system containing a gold precursor, hydrochloric acid, and water to load gold nanoparticles onto the MXene nanosheets, with nano-gap formations between adjacent gold nanoparticles, thus obtaining a flexible SERS substrate.

[0014] Preferably, the specific preparation method of CP-MXene is as follows: A flexible substrate was placed in a mixed solution of etchant and Ti3AlC2 and allowed to react at room temperature. The Al layer was selectively etched to generate MXene nanosheets, which were then deposited in situ on the surface of the flexible substrate to form a continuous conductive network structure, thus obtaining CP-MXene.

[0015] Preferably, the etching agent is obtained by mixing hydrochloric acid and fluoride salt; the ratio of hydrochloric acid to fluoride salt is 20 mL: 1 g to 2 g, and the concentration of hydrochloric acid is 9 mol / L.

[0016] Preferably, the reaction time at room temperature is 24h to 36h.

[0017] Preferably, Au nanoparticles undergo rapid in-situ reduction and nucleation, exhibiting chemical and biological inertness; furthermore, the plasma has a high energy multiplication factor, coupled with dual hotspots of MXene, resulting in stable signals.

[0018] Preferably, the molar ratio of gold precursor to hydrochloric acid is 0.1–0.2:10. -3The gold precursor is HAuCl4·4H2O.

[0019] Preferably, the electrochemical deposition time is 3 to 8 minutes. The longer the deposition time, the more Au nanoparticles are deposited on the surface, and the stronger the SERS signal.

[0020] Preferably, before depositing MXene nanosheets in situ on the surface of the flexible substrate, the flexible substrate is acidified and the surface of the carbon paper is cleaned to remove various impurities.

[0021] The third objective of this invention is to provide a method for detecting thiophanate-methyl using a flexible SERS substrate. Specifically, the method involves placing the flexible SERS substrate in a test solution containing thiophanate-methyl to react and then detecting the signal of thiophanate-methyl.

[0022] Preferably, the detection limit of the flexible SERS substrate for thiophanate-methyl is 0.00923 μM.

[0023] Compared with the prior art, the present invention has the following technical effects: 1. This invention involves in-situ growth of MXene nanosheets on a flexible substrate, followed by uniform loading of gold nanoparticles onto the MXene nanosheets, with nano-gap formations between adjacent gold nanoparticles, thus creating uniformly distributed nano-gap "hot spots." The in-situ deposition of MXene nanosheets and their strong bonding with the flexible substrate, along with the Au nanoparticles loaded on the MXene surface, result in a tight bond between the three. Simultaneously, the LSPR effect of the Au nanoparticles and the synergistic enhancement effect of the high conductivity and high specific surface area of ​​the MXene material significantly enhance the Raman signal intensity of thiophanate-methyl. Furthermore, the specific interaction between the functional groups on the MXene surface and TPM molecules endows the substrate with high selective recognition capability for TPM, thereby achieving highly sensitive and selective detection of thiophanate-methyl in fruit samples. This invention solves the technical problems of weak bonding between metal nanoparticles and flexible substrates in existing SERS substrates, leading to poor signal uniformity and reproducibility, as well as weak anti-interference ability in complex matrices.

[0024] 2. The flexible SERS substrate prepared by this invention exhibits extremely high detection sensitivity for TPM, with a detection limit as low as 0.00923 μM, which is far below the maximum residue limit stipulated by national standards and the European Union, and can meet the requirements for trace detection.

[0025] 3. The flexible SERS substrate of this invention fully utilizes the strong localized surface plasmon resonance effect of Au nanoparticles and the high conductivity and large specific surface area of ​​MXene materials, resulting in a significant synergistic enhancement effect and significantly improving the intensity of the Raman signal; its enhancement factor for Rhodamine 6G can reach 9.776 × 10⁻⁶. 5Meanwhile, the functional groups on the MXene surface have specific interactions with TPM molecules, which helps to selectively enrich TPM in complex matrices and reduce interference.

[0026] 4. The Au nanoparticles on the flexible SERS substrate of the present invention are uniformly distributed. The relative standard deviation of the TPM detection signal of substrates prepared at different sites and in different batches on the same substrate is less than 20%, and the SERS signal can still be maintained at more than 92% after 30 days of storage, showing good reproducibility and long-term stability.

[0027] 5. The synthesis of this invention is simple and easy to control, portable, highly sensitive, reproducible and stable, providing a new approach for the rapid and accurate detection of TPM in food and agricultural products. Attached Figure Description

[0028] Figure 1 The images shown are SEM images and EDS mapping images of carbon paper, CP-MXene, CP-MXene@Au, and CP-MXene@Au from Example 1. Specifically, a is the SEM image of carbon paper at a 2μm scale; b is the SEM image of carbon paper at a 200nm scale; c is the SEM image of CP-MXene at a 2μm scale; d is the SEM image of CP-MXene at a 200nm scale; e is the SEM image of CP-MXene@Au at a 2μm scale; f is the SEM image of CP-MXene@Au at a 200nm scale; g is the EDS mapping image of CP-MXene@Au; h represents C; i represents O; j represents Ti; and k represents Au.

[0029] Figure 2 The image shows the XPS spectrum of CP-MXene@Au prepared in Example 1. In the image, a is the full spectrum of CP-MXene@Au; b is the high-resolution XPS spectrum of Ti; and c is the high-resolution XPS spectrum of Au.

[0030] Figure 3 The XRD patterns of carbon paper, CP-MXene, and CP-MXene@Au in Example 1 are shown.

[0031] Figure 4 The SERS diagrams of R6G detected by CP-MXene@Au at different deposition times in Example 2 are shown.

[0032] Figure 5 The SERS spectra of R6G at 20 random points on the CP-MXene@Au substrate and the changes in Raman intensity at different Raman shifts are shown. (a) shows the SERS spectra of R6G at 20 random points on the CP-MXene@Au substrate; (b) shows the SERS spectra at 617 cm⁻¹. -1The change in Raman intensity at point (c) is 1359 cm. -1 The change in Raman intensity at point (d) is 1512 cm. -1 The change in Raman intensity at the location.

[0033] Figure 6 The SERS spectra of TPM solutions at different concentrations are shown.

[0034] Figure 7 1039cm -1 The calibration curve for TPM varies with its concentration. Detailed Implementation

[0035] As described in the background section, in analyte detection technology, SERS-based ultrasensitive sensing platforms, with their unique molecular sensing technology, provide vibrational fingerprints of molecules present in analytes, making them a highly promising detection method. SERS, as an important variant of Raman spectroscopy, generates strong electromagnetic field enhancement regions, or "hot spots," around metal nanostructures by exciting localized surface plasmon resonances. When molecules approach these "hot spots," their Raman signals are greatly enhanced, enabling single-molecule level detection while accurately providing structural and chemical information of the probe molecules. This superior performance of high sensitivity, high specificity, high precision, and non-destructive testing makes SERS a promising candidate for applications in many fields, including biomedicine, food safety monitoring, and environmental pollutant analysis.

[0036] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0037] Unless otherwise specified, all reagents used in this invention are commercially available, and all methods used are conventional techniques in the art.

[0038] Example 1 A flexible SERS substrate for detecting thiophanate-methyl includes the following steps: Step 1: Preparation of CP-MXene 1.6 g of lithium fluoride was dissolved in 20 mL of 9 mol / L HCl solution, and then 1.0 g of Ti3AlC2 powder was slowly added to obtain the etching solution.

[0039] A 1cm × 1.5cm carbon paper was placed in 15mol / L concentrated nitric acid and hydrothermally treated at 100℃ for 2 hours. After the reaction was completed, the carbon paper was cleaned to obtain pretreated carbon paper, denoted as CP.

[0040] The CP was vertically suspended in the etching solution and left to stand at room temperature for 24 hours. During this process, the Al layer in Ti3AlC2 was selectively etched to form Ti3C2T. x Nanosheets, and Ti3C2T x Nanosheets are deposited in situ on the surface of CP fibers under electrostatic attraction. After separation, CP loaded with MXene is obtained.

[0041] Remove the MXene-loaded CP and rinse it alternately with ethanol and deionized water until the pH of the washing solution is >5. Then, immerse the MXene-loaded CP in fresh deionized water and perform shaking for 10 min followed by sonication for 15 min. Repeat twice to remove loosely attached Ti3C2T. x The flakes and residual salts were separated to obtain CP-MXene, which was then stored in a humid state at 4°C for later use.

[0042] Step 2, Preparation of CP-MXene@Au: A three-electrode system was used on an electrochemical workstation. 4.2 mL of 24 mmol / L HAuCl4·4H2O and 400 μL of 10 mol / L concentrated hydrochloric acid were diluted to 10 mL with deionized water to obtain the electrolyte. Using CP-MXene composite material as the working electrode, Ag / AgCl as the reference electrode, and platinum wire as the counter electrode, deposition was performed in the electrolyte at -0.6 V for 7 min to obtain a flexible SERS substrate, denoted as CP-MXene@Au.

[0043] Example 2 A flexible SERS substrate for detecting thiophanate-methyl is basically the same as the method in Example 1, except that the deposition time is different.

[0044] Test 1.

[0045] like Figure 1 As shown in a and b, the surface of the original carbon paper exhibits a typical fibrous structure, with loosely arranged fibers, a smooth surface, and no obvious particle adhesion. Figure 1 As shown in c and d, in the CP-MXene prepared after the introduction of MXene, MXene nanosheets are uniformly coated on the surface of carbon paper fibers, forming a continuous conductive network structure, which significantly improves the specific surface area and conductivity of CP-MXene. Figure 1 As shown in e and f, in CP-MXene@Au prepared by further loading Au nanoparticles, a large number of uniformly sized Au nanoparticles are densely and uniformly distributed on the MXene coating layer, forming a distinct "hot spot" structure. These "hot spots" are composed of nano-gap structures between adjacent Au nanoparticles, which are expected to significantly enhance the local electromagnetic field, thereby improving the performance of SER. Figure 1 As shown in g~k, the EDX elemental mapping image further demonstrates the uniform distribution of C, O, Ti, and Au elements in CP-CMOF@Au.

[0046] from Figure 1 The SEM results clearly show the structural evolution process from the original carbon paper to CP-MXene and then to CP-MXene@Au, verifying the successful coating of MXene on the surface of carbon paper fibers and the high-density uniform distribution of Au nanoparticles on the MXene coating layer.

[0047] Test 2.

[0048] like Figure 2 As shown in a, the CP-MXene@Au surface is mainly composed of Ti, C, O, and Au elements. Figure 2 As shown in b, in the Ti 2p high-resolution spectrum, the Ti-C peak at 455.5 eV indicates that the MXene structure is preserved, while the Ti-O peaks at 458.7 eV and 464.2 eV reveal surface oxidation, possibly forming TiO2 or titanium hydroxyl oxide. Figure 2 As shown in c, in the Au4f spectrum, the main peak at 84.0 eV corresponds to the metallic state Au. 0 The values ​​indicate that the Au precursor has been effectively reduced; while the weak peaks at 86.8 eV and 87.9 eV indicate that a small amount of Au remains. 3+ Residues may be related to surface ligands or chloride ions. In summary, XPS results confirm that Au nanoparticles were successfully loaded onto the MXene surface, and that the material surface exhibits a certain degree of oxidation and functional group modification.

[0049] Test 3.

[0050] like Figure 3 As shown, the original carbon paper only exhibits a broad graphitic (002) peak at 2θ≈26°, corresponding to the disordered carbon structure of the carbon paper itself. After introducing MXene, CP-MXene, in addition to retaining the (002) carbon peak of the carbon paper, shows a new, sharp (002) diffraction peak at 2θ≈6.3°, with an interlayer spacing of 1.4 nm, similar to Ti3C2T. xThe consistent single-layer / few-layer structure confirms that MXene was successfully exfoliated and uniformly coated on the surface of carbon paper fibers. Simultaneously, no diffraction signals from impurity phases such as TiC and TiO2 were observed, indicating that no byproducts were introduced during the etching and exfoliation process. Further loading with Au nanoparticles resulted in the appearance of characteristic peaks (111), (200), (220), and (311) of face-centered cubic Au at 38.2°, 44.4°, 64.6°, and 77.5°, respectively. The (111) and (200) peaks were particularly sharp and intense, indicating that the Au nanoparticles were highly crystalline and preferentially grew along the (111) crystal plane.

[0051] This indicates that the MXene layered structure remains intact; Au nanoparticles are uniformly anchored on the MXene surface in the form of pure metallic phase, without the presence of oxide or other impurity phases; the “CP-MXene@Au” ternary system was successfully constructed, providing a clean and highly active crystal surface basis for subsequent SERS “hot spots”.

[0052] Test 4.

[0053] Performance tests were conducted using CP-MXene@Au substrates with different deposition times as described in Example 2. Figure 4 As shown, using CP-MXene@Au from Example 2 as the SERS substrate to detect Rhodamine 6G, the optimal deposition time was 7 min.

[0054] Enhancement factor determination.

[0055] In SERS studies, the enhancement factor (EF) is a key parameter used to measure the substrate's ability to enhance Raman signals. Using CP-MXene@Au from Example 1 as the SERS substrate and Rhodamine 6G (R6G) as the analytical probe, the EF value of CP-MXene@Au as the SERS substrate was determined using the formula for calculating the enhancement factor.

[0056] .

[0057] Among them, I SERS C represents the intensity of the Raman characteristic peak measured on the SERS substrate; SERS The concentration of R6G; I Ref C represents the Raman intensity measured on an unreinforced substrate. Ref The concentration of R6G in the reference experiment.

[0058] Analysis of R6G at 612cm −1 The characteristic vibration modes at that location were calculated to have an average enhancement factor of 9.776 × 10⁻⁶. 5 .

[0059] Reproducibility and stability testing.

[0060] To evaluate the reproducibility of CP-MXene@Au as a SERS substrate, TPM signals were tested at 20 random sites on the same substrate and 10 samples from different batches of substrates. A relative standard deviation of <10% was required to ensure reproducibility. Figure 5 As shown. For stability testing, the retention rate of the TPM signal on the test substrate within 5 to 50 days is tested. If the intensity attenuation is <15%, it indicates that the substrate has good stability and practical application potential.

[0061] Experimental results show that the relative standard deviation of 20 random sites on the same substrate is less than 20%; and the signal is retained at 92% after 30 days of storage. This indicates that CP-MXene@Au as a SERS substrate has good reproducibility and stability, and can meet the needs of practical detection.

[0062] Test 5.

[0063] To evaluate the TPM detection performance of CP-MXene@Au, a concentration of 10 was added to the sensing system. -4 mol / L, 10 -5 mol / L, 10 -6 mol / L, 10 -7 mol / L, 10 -8 mol / L, 10 -9 mol / L and 10 -10 Verification was performed using a mol / L TPM standard solution. (The solution was prepared at 1039 cm⁻¹.) -1 Plot a standard working curve with the characteristic peak intensity at a given location as the ordinate and the logarithm of the TPM concentration as the abscissa.

[0064] like Figure 6 As the concentration of the TPM standard solution increased, the Raman signal of the sensing system showed a significant concentration-dependent enhancement. This is mainly attributed to two mechanisms: First, higher concentrations of TPM molecules specifically bind to the surface of gold nanoparticles in CP-MXene@Au through their specific functional groups, increasing the coverage density of the analyte in the SERS hotspot region. Second, TPM molecules can act as a connecting bridge to induce the controllable aggregation of Au nanoparticles, forming more "hotspot" structures with strong electromagnetic field enhancement effects, thereby significantly improving the Raman signal intensity and detection sensitivity.

[0065] like Figure 7 By analyzing TPM at 1039cm -1Raman intensity changes at a specific location were analyzed, revealing a strong linear relationship between signal intensity and TPM concentration. The fitted regression equation was Y = 1098.41X + 8908.15, where Y is 1039 cm⁻¹. -1 The characteristic peak intensity is given, where X is the logarithm of the TPM concentration, and R² = 0.992. Calculations show that this method has a detection limit for TPM as low as 0.00923 μM, which is far below the national standards and the EU's maximum residue limits for fruits.

[0066] The above results indicate that the CP-MXene@Au constructed in this embodiment of the invention can be used as a SERS substrate for highly sensitive and quantitative SERS detection of TPM.

[0067] Test 6.

[0068] TPM standard solution (100 mg / L) -1 Dilute acetonitrile to 1 mg / L -1 2mg L -1 and 4mg L -1 Working solution. Apply to the surface of a single fruit (≈200 cm²) using a micropipette. 2 Add 100µL evenly and allow to air dry for 30 min. For fruit samples (apples, grapes, pears), the pretreatment process follows the procedure outlined in "Determination of Residues of 450 Pesticides and Related Chemicals in Fruits and Vegetables by Liquid Chromatography-Tandem Mass Spectrometry" (GB 207769-200).

[0069] Taking an apple as an example, cut the whole apple into small pieces, accurately weigh 2.00g and place it in a 50mL centrifuge tube. Add 10mL of 0.1% formic acid-acetonitrile and homogenize at 15000r / min for 1min. Then add 1g of NaCl and 2g of anhydrous MgSO4, immediately shake by hand for 30s, homogenize again for 1min, centrifuge at 4000r / min for 5min, and take 6mL of supernatant. Add 15mg of N-propylethylenediamine powder and 900mg of anhydrous MgSO4 to the supernatant for purification, vortex for 30s, centrifuge at 4000r / min for 3min, and take 4mL of supernatant. Blow under nitrogen at 35℃ until nearly dry, redissolve in 200µL of ultrapure water, and filter through a 0.22µm organic filter membrane to obtain the test solution.

[0070] The CP-MXene@Au was immersed in the test solution, dried in a vacuum drying oven, and then subjected to Raman detection.

[0071] It should be noted that when numerical ranges are involved in this invention, it should be understood that the two endpoints of each numerical range, as well as any value between the two endpoints, can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described in this invention to avoid redundancy. Although preferred embodiments of this invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments, and all such changes and modifications fall within the scope of this invention.

[0072] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. If these modifications and variations fall within the scope of equivalents of this invention, then this invention also intends to include these modifications and variations.

Claims

1. A flexible SERS substrate for detecting thiophonic methyl, characterized in that, The flexible SERS substrate is composed of a flexible substrate, MXene nanosheets grown in situ on the surface of the flexible substrate, and gold nanoparticles loaded on the MXene nanosheets; and a nanogap is formed between adjacent gold nanoparticles.

2. The flexible SERS substrate for detecting thiophonic methylcarbamate according to claim 1, wherein, The nanogap is 1-3 nanometers.

3. The flexible SERS substrate for detecting thiophonic methylcarbamate according to claim 1, wherein, MXene nanosheets are Ti3C2T x nanosheets; wherein x is 1.8-2.2; the flexible substrate is carbon paper.

4. A method for preparing a flexible SERS substrate for detecting thiophonic methylcarbamate according to any one of claims 1 to 3, characterized in that, The method comprises the following steps: Depositing MXene nanosheets in situ on the surface of the flexible substrate to form a continuous conductive network structure, to obtain CP-MXene; Electrochemically depositing the CP-MXene in a mixed solution system containing a gold precursor, hydrochloric acid, and water, to load gold nanoparticles on the MXene nanosheets, and form a nanogap between adjacent gold nanoparticles, to obtain the flexible SERS substrate.

5. The method for preparing a flexible SERS substrate for detecting thiophonic methyl according to claim 4, wherein, The specific preparation method of the CP-MXene is as follows: The flexible substrate is placed in a mixed solution of an etchant and Ti3AlC2, and is left to react at room temperature; the Al layer is selectively etched to generate MXene nanosheets, which are deposited in situ on the surface of the flexible substrate to form a continuous conductive network structure, to obtain the CP-MXene.

6. The method for preparing a flexible SERS substrate for detecting thiophonic methyl according to claim 5, wherein, The etchant is obtained by mixing hydrochloric acid and a fluorine salt; The amount ratio of the hydrochloric acid to the fluorine salt is 20 mL:1-2 g, and the concentration of the hydrochloric acid is 9 mol / L.

7. The method for preparing a flexible SERS substrate for detecting thiophonic methyl according to claim 5, wherein, The reaction is left to react at room temperature for 24-36 hours.

8. The method for preparing a flexible SERS substrate for detecting thiophonic methyl according to claim 4, wherein, The molar ratio of gold precursor and hydrochloric acid is 0.1-0.2:10 -3 ; The gold precursor is HAuCl4·4H2O; The electrochemical deposition is performed for 3-8 minutes.

9. Use of a flexible SERS substrate for the detection of methylic thiobacillus, characterized in that, The flexible SERS substrate is the flexible SERS substrate for detecting thiabendazole according to any one of claims 1-3.

10. Use of the flexible SERS substrate according to claim 9 for the detection of methicillin, characterized in that, The specific application method is: the flexible SERS substrate is placed in a to-be-tested liquid containing thiabendazole to react, and the signal of the thiabendazole is detected; The detection limit of the flexible SERS substrate for thiabendazole reaches 0.00923 μM.

Images