Preparation method of Ti3C2-PDDA-Au-coated AgNPs composite substrate material as well as product and application of Ti3C2-PDDA-Au-coated AgNPs composite substrate material

Abstract

The invention discloses a preparation method of a Ti3C2-PDDA-Au-coated AgNPs composite substrate material as well as a product and application of the Ti3C2-PDDA-Au-coated AgNPs composite substrate material, and belongs to the technical field of sensors. According to the invention, a Ti3C2 nanosheet and Au (at) AgNPs (gold core and silver shell nanoparticles) are prepared, and a Ti3C2-PDDA-Au (at) AgNPs composite substrate is constructed by using an electrostatic self-assembly method. The composite substrate can be assembled with probe molecules to form an SERS sensor, the sensor can rapidly and sensitively detect the plasticizer in the edible oil, the sensitivity is high, the detection limit is low, the linear relation is good, a novel efficient method is provided for detection of the plasticizer in the edible oil, and the SERS sensor has important practical value for guaranteeing food safety.

Description

Technical Field

[0001] The present invention belongs to the technical field of sensors, and particularly relates to a preparation method, product and application of a Ti3C2-PDDA-Au@AgNPs composite substrate material. Background Art

[0002] Phthalic acid esters (PAEs), also known as phthalates, are a class of fat-soluble toxic compounds with a special odor. PAEs at room temperature are usually transparent, colorless oily liquids, insoluble in water but soluble in organic solvents such as methanol, ethanol, and ether. Most of them have relatively high boiling points and low melting points. There are hundreds of types of PAEs, and common phthalic acid esters include dimethyl phthalate (DMP), bis(2-ethylhexyl) phthalate (DEHP), dibutyl phthalate (DBP), di-n-octyl phthalate (DNOP), diethyl phthalate (DEP), and butyl benzyl phthalate (BBP).

[0003] Due to its own structural characteristics, plasticizers can reduce the intermolecular force. When added to polymers, they can not only reduce the polymer viscosity but also increase its extensibility and flexibility. However, with the large-scale use of plasticizers, their drawbacks have gradually emerged. After plasticizers accumulate in the human body to a certain extent, they not only interfere with the human endocrine system but also have certain adverse effects on the reproductive organs, immune and digestive systems, and even the reproductive system development of offspring.

[0004] The digestive system is the main route for plasticizers to enter the human body. When using plastic products to package food, some plasticizers will transfer from the plastic packaging to the food, causing food contamination. Currently, there is research evidence that Xu Ying et al. detected 15 target plasticizers in several common edible oil samples on the market and found that plasticizer components could be detected in different degrees in the samples, while no plasticizer components were detected in the edible oil samples stored in glass bottles. Therefore, it can be judged that the plasticizers in food come from plastic packaging containers.

[0005] As one of the most serious pollutants in the 21st century, plasticizers not only cause great harm to the ecological environment but also pose a certain threat to human life and health. Currently, the main way for plasticizers to enter the human body is through food intake, and the sources of plasticizers in food can be roughly divided into two aspects: one is the packaging materials in contact with food. Due to their good extensibility and flexibility, plasticizers are widely used in the industrial production of plastic products. As an important part of food packaging, plastic products are very popular because of their portability and low cost. However, the plasticizers in plastic packaging can seep into food. For example, food stored in plastic containers or plastic wrap is very likely to contain plasticizers; the other is the plasticizers present in the food processing process. Plasticizers in the soil environment or water enter the human body along the food chain. In view of the above phenomena, it is very important to minimize the intake of plasticizer-containing food from the source and strengthen the detection of plasticizers in plastic-packaged food.

[0006] Currently, when detecting plasticizers in actual samples, due to certain requirements of traditional detection techniques for the purity of the target substance, it is necessary to carry out relatively cumbersome pretreatment such as purification and extraction of the samples. And emerging detection techniques such as immunoassay and fluorescence analysis have problems such as low sensitivity. Therefore, developing an efficient and sensitive detection method to achieve non-destructive, simple and rapid detection of plasticizers in oils and fats has important practical value for ensuring food safety. Summary of the Invention

[0007] In view of the above technical problems, the present invention proposes a preparation method, product and application of a Ti3C2-PDDA-Au@AgNPs composite substrate material. The present invention establishes a new surface-enhanced Raman scattering sensor detection method for two-dimensional materials / noble metals, explores the performance of new sensors in detecting plasticizers in actual samples, provides more ways for studying and improving the detection level of plasticizers in food, controlling the harm of plasticizers to the human body from the source, and effectively protecting the health of consumers. At the same time, it also provides a certain technical reference for expanding the residual detection methods of plasticizers in food in the future.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] One of the objects of the present invention is to provide a preparation method of a Ti3C2-PDDA-Au@AgNPs composite substrate material, comprising the following steps:

[0010] Dropwise add a poly(diallyldimethylammonium chloride) solution to the Ti3C2 nanosheet solution, stir at room temperature, centrifuge to discard the supernatant, wash the obtained precipitate, and then redisperse it in deionized water to obtain a positively charged Ti3C2 nanosheet solution;

[0011] Add the positively charged Ti3C2 nanosheet solution to the Au@AgNPs solution, stir, centrifuge to discard the supernatant, wash the obtained precipitate, and then redisperse it in deionized water to obtain the Ti3C2-PDDA-Au@AgNPs composite substrate material.

[0012] Optionally, the preparation method of the Ti3C2 nanosheet solution includes the following steps: Add lithium fluoride to the hydrochloric acid solution, heat and stir, then add the Ti3AlC2 precursor, continue to heat and stir, centrifuge to discard the supernatant, wash the obtained precipitate until it is neutral, and after the precipitate shows an expansion phenomenon, redisperse the obtained precipitate in deionized water, ultrasonicate and centrifuge in an ice bath to obtain a dark green supernatant, which is the Ti3C2 nanosheet solution.

[0013] Further, during the preparation of the Ti3C2 nanosheet solution:

[0014] The dosage ratio of the lithium fluoride, hydrochloric acid solution and Ti3AlC2 precursor is 1.6 g∶20 mL∶1 g; and / or

[0015] The conditions for the heating and stirring are: stirring at 45 °C for 15 min; and / or

[0016] The conditions for the continued heating and stirring are: stirring at a temperature of 45 °C and a rotation speed of 433 rpm for 24 h; and / or

[0017] The conditions for the centrifugation are: centrifuging at a rotation speed of 3500 rpm for 10 min; and / or

[0018] The conditions for the ultrasonication and centrifugation are: ultrasonication for 50 min, and then centrifuging at a rotation speed of 3500 rpm for 1 h.

[0019] Optionally, the preparation method of the Au@AgNPs solution includes the following steps: Add ascorbic acid to the AuNPs solution, stir at room temperature, then add the silver nitrate solution, and continue to stir at room temperature until the solution changes from purple-red to orange-yellow, and filter to obtain the Au@AgNPs solution.

[0020] Optionally, the preparation method of the AuNPs solution is: Mix the HAuCl4·4H2O solution with deionized water and heat it in an oil bath until the solution is slightly boiling, add the sodium citrate solution under stirring, and keep the solution slightly boiling until it changes from colorless to purple-red, and then naturally cool to room temperature and filter to obtain the AuNPs solution.

[0021] Further, during the preparation of the AuNPs solution: The volume ratio of the HAuCl4·4H2O solution, deionized water and sodium citrate solution is 1∶99∶1.

[0022] In the process of preparing the Au@AgNPs solution: the volume ratio of the AuNPs solution, ascorbic acid, and silver nitrate solution is 10∶1∶(1.5 - 2.5).

[0023] Further, in the process of preparing the positively charged Ti 3C2 nanosheet solution:

[0024] The volume ratio of the Ti3C2 nanosheet solution to the polydiallyldimethylammonium chloride solution is 15∶0.5.

[0025] The conditions for centrifugation are: centrifuging at 3500 rpm for 1 h.

[0026] Further, in the process of preparing the Ti3C2-PDDA-Au@AgNPs composite substrate material:

[0027] The volume ratio of the Au@AgNPs solution to the positively charged Ti3C2 nanosheet solution is 6∶0.5; and / or

[0028] The conditions for centrifugation are: centrifuging at 4000 rpm for 20 min.

[0029] The second object of the present invention is to provide a Ti3C2-PDDA-Au@AgNPs composite substrate material prepared by the above preparation method.

[0030] The third object of the present invention is to provide a SERS sensor, using the Ti3C2-PDDA-Au@AgNPs composite substrate material as a carrier and a cationic dye as a probe molecule.

[0031] Further, the cationic dye includes one of rhodamine 6G, crystal violet, and malachite green.

[0032] The fourth object of the present invention is to provide an application of the SERS sensor in the field of plasticizer detection.

[0033] The fifth object of the present invention is to provide a method for detecting plasticizers in oils and fats, using the SERS sensor to detect plasticizers in oils and fats.

[0034] Compared with the prior art, the present invention has the following advantages and technical effects:

[0035] The present invention constructs a composite substrate based on two-dimensional nanosheet MXene and noble metal Au@AgNPs, establishes a SERS sensing platform capable of accurately and rapidly determining plasticizers in edible oils, and successfully applies it to the detection of plasticizers in common edible oils on the market.

[0036] The present invention prepared Ti3C2 nanosheets and Au@AgNPs by a reduction method; and characterized the surface morphology, molecular structure, etc. of the prepared materials by TEM, SEM, AFM, XRD, etc. The Ti3C2 nanosheets can detect R6G, CV, and MG at 1×10 -8 M. The Ti3C2 nanosheets were modified with PDDA, and electrostatic self-assembly with the synthesized bimetallic Au@AgNPs of different sizes was performed to obtain the Ti3C2-PDDA-Au@AgNPs composite substrate. According to the Raman signal of R6G on the composite substrate, Ti3C2-PDDA-Au@AgNPs was screened out as the optimal substrate.

[0037] The present invention detected DMP and DEHP in methanol solution based on the Ti3C2-PDDA-Au@AgNPs SERS sensor. The results showed that the detection limits of DMP and DEHP in the methanol standard solution were as low as 1×10 -13 M, and there was a good linear relationship between the SERS signal and the logarithm of the concentration in the range of 1×10 -6 ~10 -13 M, and the linear correlation coefficients (R 2 ) were all higher than 0.99. When detecting PAEs in actual edible oil samples, the detection limits of the sensor for DMP and DEHP samples were both 1×10 -12 M, and the sample concentration maintained a good linear relationship in the range of 1×10 -9 ~10 -12 M, and the R 2 were 0.9997 and 0.9932 respectively. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0039] Figure 1 is the TEM morphology diagram of the Ti3C2 nanosheet solution;

[0040] Figure 2 is the AFM diagram of the Ti3C2 nanosheet solution;

[0041] Figure 3 is the XRD pattern of the Ti3AlC2 precursor and the Ti3C2 nanosheet solution;

[0042] Figure 4 is the Raman spectrum of the Ti3C2 nanosheet solution;

[0043] Figure 5 is the diagram of the Ti3C2 nanosheet solution before and after being stored at 4°C for one week;

[0044] Figure 6 TEM images of AuNPs; where, a: 50 nm, b: 500 nm;

[0045] Figure 7 TEM and EDS images of bimetallic Au@AgNPs;

[0046] Figure 8 UV-visible spectra of AuNPs and bimetallic Au@AgNPs;

[0047] Figure 9 Zeta potential diagrams of Ti3C2 nanosheets, PDDF-modified Ti3C2, bimetallic Au@AgNPs, and composite substrates;

[0048] Figure 10 UV-visible light absorption spectra of Ti3C2 nanosheets, Au@AgNPs, and composite substrates;

[0049] Figure 11 TEM images of composite substrates; where, a: 100 nm, b: 500 nm;

[0050] Figure 12 EDS images of different elements on the composite substrates;

[0051] Figure 13 Raman signals of three probes, R6G (a), CV (b), and MG (c), on Ti3C2 nanosheets;

[0052] Figure 14 SERS spectra of DMP and DEHP methanol standard solutions on the sensor; where, a: Raman spectra of DMP standard solutions with different concentrations on the Ti3C2-PDDA-Au@AgNPs sensor; b: Linear relationship diagram of the SERS signal of DMP methanol standard solution at 1271 cm -1 versus the logarithm of the concentration; c: Raman spectra of DEHP standard solutions with different concentrations on the Ti3C2-PDDA-Au@AgNPs sensor; d: Linear relationship diagram of the SERS signal of DEHP methanol standard solution at 1273 cm -1 versus the logarithm of the concentration;

[0053] Figure 15 Determination of phthalates DMP and DEHP in actual sample oils by the sensor; where, a is the SERS spectra detected by the sensor for DMP actual sample solutions with different concentrations; b is the SERS signal of the DMP sample solution at 1271 cm 1Standard curve of the linear relationship between the SERS signal and the logarithm of the concentration at [specific position]; c is the SERS spectrum of the DEHP actual sample solution with different concentrations detected on the sensor; d is the DEHP sample solution at 1273 cm 1 Standard curve of the linear relationship between the SERS signal and the logarithm of the concentration at [specific position]. Detailed implementation mode

[0054] The various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0055] It should be understood that the terms used in the present invention are only for describing specific embodiments and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0056] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0057] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific implementation modes of the present invention specification, which are obvious to those skilled in the art. Other implementation modes obtained from the present invention specification are obvious to those skilled in the art. The present invention specification and examples are only exemplary.

[0058] Regarding the use of "comprising", "including", "having", "containing", etc. in this article, they are all open-ended terms, meaning including but not limited to.

[0059] The corresponding Chinese meanings of the English abbreviations used in the present invention are as follows:

[0060] PAEs: Phthalic acid esters, plasticizers;

[0061] DEHP: Bis(2-Ethylhexyl)phthalate, di(2-ethylhexyl) phthalate;

[0062] DMP: Dimethyl phthalate, Dimethyl phthalate;

[0063] GC: Gas chromatography, Gas chromatography;

[0064] GC-MS: Gas chromatography-mass spectrometry, Gas chromatography-mass spectrometry;

[0065] HPLC: High performance liquid chromatography, High performance liquid chromatography;

[0066] SERS: Surface-enhancement Raman scattering, Surface-enhancement Raman scattering;

[0067] CM: Chemical enhancement, Chemical enhancement;

[0068] EM: Electromagnetic enhancement, Electromagnetic enhancement;

[0069] LSPR: Localized surface plasmon resonance, Localized surface plasmon resonance;

[0070] XRD: X-ray diffraction, X-ray diffraction;

[0071] TEM: Transmission wlectron microscope, Transmission electron microscope;

[0072] EDS: energy dispersive spectrometer, Energy dispersive X-ray spectrometer;

[0073] AFM: Atomic force microscope, Atomic force microscope;

[0074] SEM: Scanning electron microscope, Scanning electron microscope;

[0075] PDDA: Poly dimethyl diallyl ammonium chloride, Poly dimethyl diallyl ammonium chloride;

[0076] R6G: Rhodamine 6G, Rhodamine 6G;

[0077] CV: Crystal violet, crystal violet;

[0078] MG: malachite green, malachite green;

[0079] MILD: Minimally intensive layer delamination, minimally intensive layer delamination.

[0080] The reagents and equipment used in the embodiments of the present invention are shown in Table 1 and Table 2.

[0081] Table 1 Main reagents and materials used in the experiment

[0082]

[0083] Table 2 Main instruments and equipment used in the experiment

[0084]

[0085] The oil used in the embodiments of the present invention is Hu Jihua peanut oil purchased from Ginza Supermarket.

[0086] Preparation of standard solutions:

[0087] 1) Preparation of standard solutions of probe molecules rhodamine 6G (R6G), crystal violet (CV), and malachite green (MG): Weigh a certain mass of R6G, CV, and MG standards, add deionized water, and dissolve them by ultrasonic treatment. Then, prepare a stock solution with a concentration of 1×10 -3 M. Pipette 1 mL of the stock solution into a 10 mL volumetric flask, add deionized water to the mark, and successively dilute it to 1×10 -5 M - 1×10 -14 M R6G standard solution, and 1×10 -5 M - 1×10 -8 M CV and MG standard solutions. Store the solutions in a 4°C refrigerator for later use in the next experiment.

[0088] 2) Preparation of DMP and DEHP standard solutions: Weigh a certain amount of DMP and DEHP, and prepare a standard stock solution with a concentration of 1×10 -4 M using methanol; Pipette 1 mL of the stock solution into a 10 mL volumetric flask, and make up the volume with methanol to obtain 1×10 -5 M DEHP and DMP standard solutions; Prepare 1×10 -6 M - 1×10 -14 M DEHP and DMP standard solutions successively according to the above method. Store the standard solutions in the dark at 4°C for later use.

[0089] The technical solution of the present invention will be further described below through embodiments.

[0090] Example 1

[0091] Preparation of nanosheets and construction of sensors:

[0092] I) Preparation of Ti3C2 nanosheet solution:

[0093] Weigh 1.6 g of lithium fluoride (LiF) and add it to a polytetrafluoroethylene beaker containing 20 mL of hydrochloric acid (9 M). Heat the solution to 45 °C and stir continuously for 15 min. Then add 1 g of Ti3AlC2 precursor. After the bubbles disappear, gently cover the lid and magnetically stir the solution at 45 °C and 433 rpm for 24 h. Then transfer the solution to a 50 mL centrifuge tube and centrifuge it at 3500 rpm for 10 min. Discard the supernatant, and then wash the precipitate with deionized water multiple times at a speed of 3500 rpm until the supernatant is neutral. After observing the swelling phenomenon of the precipitate, redisperse the precipitate in deionized water, ultrasonicate it in an ice bath for 50 min, and then centrifuge it at 3500 rpm for 1 h. The dark green supernatant is the final product, that is, the Ti3C2 nanosheet solution is obtained.

[0094] II) Synthesis of AuNPs and Au@AgNPs

[0095] 1) Preparation of AuNPs: Mix 1 mL of 1% (mass concentration) HAuCl4·4H2O solution with 99 mL of deionized water and transfer it to a round-bottomed three-necked flask. Place the round-bottomed three-necked flask in a heating magnetic stirrer oil bath and heat it gradually until the solution is in a slightly boiling state. Quickly inject 1 mL of 1% (mass concentration) sodium citrate solution under vigorous stirring. Keep the solution boiling for 18 min. The color changes from colorless to purple-red, indicating the successful synthesis of metallic AuNPs. After the solution cools naturally to room temperature, filter it through a 0.22 μm filter membrane to obtain the AuNPs solution, and store it at 4 °C for later use;

[0096] 2) Preparation of Au@AgNPs: Place 10 mL of the prepared AuNPs solution in a 25 mL beaker, add 1 mL of 1% (mass concentration) ascorbic acid solution to it, stir it at room temperature for 30 min, and then add 1.5 mL, 1.75 mL, 2 mL, 2.25 mL, and 2.5 mL of 1 mM silver nitrate solution respectively. Continue to stir at room temperature for 60 min to obtain metal nanoparticles with different silver shell thicknesses. When the solution changes from purple-red to orange-yellow, it indicates the successful synthesis of the bimetallic core-shell Au@AgNPs. Filter the solution through a 0.22 μm filter membrane respectively to obtain the Au@AgNPs bimetallic solution, collect, label, and store it at 4 °C for further experiments;

[0097] 3) Preparation of Ti3C2-PDDA-Au@AgNPs composite substrate

[0098] 1) Preparation of positively charged Ti3C2 nanosheet solution: 15 mL of the prepared Ti3C2 nanosheet solution was taken into a 25 mL beaker, and 0.5 mL of PDDA solution was slowly added dropwise. After continuous magnetic stirring for 24 h at room temperature, the mixture was centrifuged at 3500 rpm for 1 h, the supernatant was discarded, and the precipitate was washed twice with deionized water. The obtained precipitate was centrifuged twice at a centrifugal speed of 4000 rpm and 4500 rpm, respectively, for 5 min each time. The final precipitate was dispersed in deionized water to obtain a positively charged Ti3C2 nanosheet solution (i.e., PDDF-modified Ti3C2).

[0099] 2) Preparation of Ti3C2-PDDA-Au@AgNPs composite substrate: Pipette the synthesized 6mL Au@AgNPs bimetallic solution into a 10mL beaker, add 0.5mL of positively charged Ti3C2 nanosheet solution while slowly stirring at room temperature, continue stirring at the same speed for 5h to ensure that the nanosheets and bimetallic solution are fully mixed. After the reaction is completed, centrifuge the reaction solution at a speed of 4000rpm for 20min, then wash the precipitate with deionized water twice, and centrifuge the obtained precipitate twice, with centrifugal speeds of 4500rpm and 5000rpm, respectively, for 5min each time. In order to remove the bimetallic nanoparticles that are not adsorbed on the nanosheets in the mixed solution, the precipitate is redispersed in deionized water after the centrifugation, and finally the Ti3C2-PDDA-Au@AgNPs composite substrate is obtained, and the mixed solution is stored at 4°C for later use.

[0100] 4) Raman signal response of nanosheets and composite substrates to probe molecules

[0101] In order to obtain the signal sensitivity of the nanosheets, a series of different concentrations (1×10 -5 M, 1×10 -6 M, 1×10 -7 M, 1×10 -8M) probe molecules (R6G, CV, MG) were used for Raman signal testing. 200 μL of Ti3C2 nanosheets were separately drawn into a 10 mL centrifuge tube, and 5 mL of deionized water was added. After thorough mixing, 10 μL of the mixed solution was drawn and dropped onto a clean silicon wafer, and fully dried at room temperature. Use tweezers to pick up the silicon wafers and place them into 2 mL centrifuge tubes containing standard solutions of three probe molecules with different concentrations. After the silicon wafers were completely immersed in the solution for 12 hours, they were taken out with tweezers and dried naturally at room temperature. The silicon wafers were placed under a laser confocal Raman spectrometer to measure the Raman signal. The instrument parameters selected were a ×50 objective lens and an excitation wavelength of 532 nm, an excitation power of 5 mM, an excitation time of 1 s, 15 excitation times, and a spectral range of 600-1800 cm -1 .

[0102] The enhancement effect of bimetallic Au@AgNPs on SERS signal was evaluated by comparing the same concentration (10 -8 M) Signal intensity of R6G on nanosheets and composite substrates.

[0103] 5) Optimization and performance evaluation of composite substrate

[0104] In order to further improve the sensitivity of the sensor, the composite substrate was optimized. The size of the nanoparticles was adjusted during the synthesis of the metal, and five different sizes of bimetallic Au@AgNPs were combined with nanosheets to prepare Ti3C2-PDDA-Au@AgNPs composite substrates of different specifications. -11 The SERS signal test of five composite substrates was carried out by using R6G standard solution of M, and the test was repeated many times to compare the SERS signal intensity of probe molecule R6G with the same concentration on different substrates, so as to obtain the ideal composite substrate with the best SERS enhancement effect.

[0105] The SERS performance of the sensor was evaluated by taking 10 μL of the optimized composite substrate and dropping it on a dry and clean silicon wafer. The silicon wafer was immersed in different concentrations (1×10 -9 M, 1×10 -10 M, 1×10 -11 M, 1×10 -12 M, 1×10 -13 M, 1×10 -14 M) in the R6G standard solution, the signal intensity of R6G at different concentrations on the sensor was tested, the minimum detection limit of the sensor for R6G was determined, and the sensitivity of the sensor was explored; by selecting a concentration of 1×10 -11Use R6G of M to test the stability of the substrate. Place the optimized noble metal nanosheet composite substrate solution in a refrigerator at 4 °C for 30 days. Measure the intensity of the R6G Raman characteristic peak signal of the substrate at 0, 3, 7, 15, and 30 days respectively. Compare the relationship between its SERS signal intensity and time change, and explore the stability of the sensor; also select the probe molecule R6G with a concentration of 1×10 -11 M of the sensor, and test its SERS signal intensity on the sensor. Multiple batches of composite substrates were prepared in parallel. During the test, multiple regions were randomly selected from each batch of substrates for experimental testing. After baseline correction processing of the collected data, multiple spectral data were selected for signal intensity change analysis to explore the signal reproducibility of the sensor.

[0106] (VI) Determination of actual samples

[0107] Determine the contents of DMP and DEHP in peanut oil by surface-enhanced Raman scattering method. The specific operation is as follows: Pipette 4 mL of peanut oil into a 10 mL centrifuge tube, and add DMP or DEHP standard solution to the centrifuge tube to make their concentrations 1×10 -8 M, 1×10 -9 M, 1×10 -10 M, 1×10 -11 M, 1×10 -12 M and 1×10 -13 M respectively. Pipette 2 mL of the spiked sample solution into a centrifuge tube, add 2 mL of chromatographic methanol, mix on a vortex shaker, and centrifuge at 10000 rpm for 15 min. Transfer the supernatant to a brown volumetric flask and store it at 4 °C for later use.

[0108] Pipette 10 μL of the composite substrate solution onto a silicon wafer and dry it at room temperature. Use tweezers to pick up the silicon wafer and immerse it in the above methanol extract. After drying at room temperature, perform SERS detection. Repeat the experiment and add to the oil at the concentration levels of 1×10 -9 M, 1×10 -10 M, 1×10 -11 M, and calculate the recovery rate.

[0109] (VII) Calculation of enhancement factor

[0110] Calculate the enhancement factor of the Ti3C2-PDDA-Au@AgNPs sensor for the probe molecule R6G. Prepare a 0.3 M R6G standard solution. Pipette 10 μL and drop it onto a silicon wafer, dry it at room temperature, then place it on the Raman instrument stage. Select a ×50 objective lens, at a laser wavelength of 532 nm, adjust the excitation power to 0.5 mM, the integration time to 1 s, and the integration times to 15.

[0111] Calculate the enhancement factor of the composite substrate for the probe molecule R6G according to the following formula:

[0112]

[0113] In the formula, I SERS refers to the SERS signal intensity of the probe molecule R6G on the composite substrate at 1367 cm -1 , and I Raman refers to the ordinary Raman signal intensity of R6G on the silicon wafer at 1367 cm -1 . C SERS refers to the concentration of the probe molecule R6G tested on the composite substrate, and C Raman refers to the concentration of the probe molecule R6G on the silicon wafer.

[0114] Raman spectroscopy is easily affected by environmental background, baseline drift, etc. during the test. Therefore, it is necessary to use Origin software to perform baseline calibration and smoothing processing on the spectral data lines collected by the measurement.

[0115] Results and Analysis

[0116] 1. Material Characterization

[0117] 1) Characterization of Ti3C2 Nanosheets

[0118] In the present invention, a mixed solution of HCl and LiF is used as a chemical etching agent to selectively etch the Al atomic layer in the MAX phase (Ti3AlC2) of MXenes, and multi-layer Ti3C2T x nanosheets are initially obtained. After multiple centrifugations, hand shakings, and mechanical forces such as ultrasonic waves to break the multi-layers, a single-layer nanosheet solution is finally obtained. To further understand the surface morphology and structural characteristics of the single-layer Ti3C2 nanosheets, a series of material characterizations such as TEM, SEM, AFM, and XRD are now carried out on them.

[0119] Figure 1 is the TEM morphology diagram of the Ti3C2 nanosheet solution. From the figure, it can be clearly observed that the nanosheets are almost transparent, with a good morphology and slight wrinkles, and single-layer nanosheets with relatively large lateral dimensions are shown.

[0120] Figure 2 is the AFM diagram of the Ti3C2 nanosheet solution. The thickness of the nanosheet is tested at any position in the 2D diagram to obtain the height profile at the dotted line. The test results show that the thickness at the dotted line position is stepped, and due to the partial stacking of the nanosheets, there is a slight undulation in height. Among them, the thickness of two layers of nanosheets is 3.6 nm, and the thickness of a single-layer nanosheet is 1.8 nm, which conforms to the theoretical thickness of the single-layer nanosheet. The results of AFM once again confirm the successful synthesis of the single-layer Ti3C2 nanosheets.

[0121] Figure 3XRD patterns of the Ti3AlC2 precursor and the Ti3C2 nanosheet solution. According to the XRD patterns, the diffraction peaks of the precursor MAX phase Ti3AlC2 are 9.4° (002), 19° (004), 33.8° (101), 36.6° (103), 38.5° (104), and 41.6° (105), respectively. Among them, the diffraction peak (104) at 38.5° has basically disappeared in the XRD pattern of the etched product Ti3C2 after the Ti3AlC2 is etched with LiF / HCl, indicating the successful removal of the Al atomic layer in the MAX phase. In addition, the diffraction peak (002) at 9.4° in the MAX phase has shifted left to 7° after etching, and the diffraction peak (004) at 19° has also shifted left to 16.5° with an increased peak width. The significant left shift of these two diffraction peaks is caused by the increase in the interlayer spacing of the nanosheets, indicating the successful delamination of the Ti3C2 nanosheets.

[0122] Figure 4 Raman spectrum of the Ti3C2 nanosheet solution. As shown in the figure, Raman test analysis was performed on the etched Ti3C2 nanosheets. Among them, 521 cm -1 is the silicon wafer background peak. The Raman peaks of the Ti3C2 single-layer nanosheets are mainly 202 cm -1 , 287 cm -1 , 387 cm -1 , 579 cm -1 , 625 cm -1 and 723 cm -1 . Among them, the Raman peak at 202 cm -1 is mainly caused by the in-plane and out-of-plane vibrations of Ti atoms. The Raman peak at 723 cm -1 belongs to the A 1g symmetric mode of C-C vibration. The Raman peaks at 287 cm -1 , 387 cm -1 and 625 cm -1 are assigned to the vibrations of the surface functional groups of the nanosheets. After the synthesis of the nanosheets, -O, -OH, and -F functional groups are attached to the surface.

[0123] Figure 5 Images of the Ti3C2 nanosheet solution before and after being stored at 4°C for one week. It can be seen that there is no obvious change in color and no obvious oxidation phenomenon after being placed for one week under the same conditions, indicating that the Ti3C2 nanosheet solution system is more stable.

[0124] 2) Characterization of AuNPs and bimetallic Au@AgNPs

[0125] To better observe the synthesis of metal nanoparticles, the monometallic AuNPs and bimetallic Au@AgNPs synthesized in the experiment were characterized by TEM, EDS, UV, etc., and information such as the size and shape of the metal nanoparticles was obtained.

[0126] Figure 6 Figure 4 shows the TEM image of AuNPs. From Figure 6 a in it, it can be measured that the diameter of AuNPs is about 34 nm, and the shape of the nanoparticles is complete. In Figure b, it is observed that the particle size of the nanoparticle clusters is uniform and the dispersion is good.

[0127] Figure 7 Figures 5 and 6 show the TEM and EDS images of the bimetallic Au@AgNPs. According to the analysis of the TEM and EDS characterization test results of Au@AgNPs, it is found that a clear bimetallic core-shell structure can be observed from the high-magnification transmission electron microscope images. The diameter of Au@AgNPs is between 38 - 40 nm. According to the average particle size of AuNPs being about 34 nm, after calculation, the thickness of the silver shell in the bimetallic is about 2.5 nm. At the same time, the EDS image reflects that the Ag element is evenly distributed around the Au element, and both the TEM and EDS images clearly show the core-shell structure of the bimetallic.

[0128] Figure 8 Figure 7 shows the UV-visible spectra of AuNPs and bimetallic Au@AgNPs. It is observed from the spectra that AuNPs have a surface plasmon resonance peak (LSPR) at 527 nm, and Au@AgNPs have two LSPRs at 400 nm and 494 nm, corresponding to the plasmon resonance effects of the gold core and silver shell in the bimetallic core-shell structure respectively. The results of the UV-visible spectra once again confirm the successful synthesis of the bimetallic Au@AgNPs.

[0129] 3) Characterization of the composite substrate

[0130] To ensure the uniformity of the prepared SERS substrate, the present invention constructs a composite substrate by the self-assembly method. The two-dimensional nanosheet Ti3C2 with a large surface area and good hydrophilicity is selected as the substrate, and at the same time, the nanosheet is compounded with noble metal nanoparticles with a strong surface plasmon resonance effect to improve the SERS enhancement ability of the composite substrate for the detection target.

[0131] Figure 9Zeta potential diagrams of Ti3C2 nanosheets, PDDF-modified Ti3C2, bimetallic Au@AgNPs, and the composite substrate are shown. In the figure, the solution of Ti3C2 nanosheets after chemical reagent etching carries a negative charge (-32.6 mV), and the solution of bimetallic Au@AgNPs reduced by ascorbic acid also carries a negative charge (-20.5 mV). Given the principle of like charges repelling and opposite charges attracting, the negatively charged nanosheets and metal nanoparticles cannot bind firmly together. Therefore, an appropriate amount of polymer PDDA was added to the nanosheet solution during the experiment, successfully modifying the charge of the nanosheet solution from negative (-32.6 mV) to positive (+44.83 mV). Then, Ti3C2 and Au@AgNPs with opposite charges were mixed in an appropriate ratio. After multiple centrifugation and washing steps, the two materials self-assembled into a composite through electrostatic interaction. The composite substrate solution was measured to carry a positive charge (+8.52 mV).

[0132] Figure 10 UV-visible absorption spectra of Ti3C2 nanosheets, Au@AgNPs, and the composite substrate are shown. From the figure, it can be seen that there is no obvious absorption peak in the UV absorption spectrum of Ti3C2 nanosheets. Au@AgNPs have two absorption peaks, and the absorption peaks at 400 nm and 494 nm are both the surface plasmon resonance peaks of bimetallic Au@AgNPs. Moreover, the width of the surface plasmon absorption peak increases. The UV-visible spectrum of the mixed solution further proves the successful construction of the sensor.

[0133] To further verify the successful synthesis of the composite substrate, high-magnification and low-magnification transmission electron microscopy (TEM) scans were performed on the composite substrate. Figure 11 TEM images of the composite substrate are shown. According to the scanning results in Figure a, the bimetallic core-shell structured Au@AgNPs are firmly adsorbed on the nanosheets. In Figure b, the bimetallic nanoparticles cover a large area of the nanosheets.

[0134] EDS mapping characterization of the composite substrate was carried out simultaneously with TEM to test the distributions of metal elements (Au, Ag) and nanosheet Ti3C2 elements (Ti, C, O, F). Figure 12 EDS images of different elements on the composite substrate are shown. It can be seen that the metal elements Au and Ag are evenly distributed on the nanosheets.

[0135] Through a series of characterization results of the composite substrate, the successful binding of Au@AgNPs and Ti3C2 under electrostatic interaction was confirmed, marking the successful preparation of the self-assembled Ti3C2-PDDA-Au@AgNPs composite enhanced SERS substrate.

[0136] 2. Raman signal enhancement study of Ti3C2 nanosheets

[0137] Rhodamine 6G (R6G), Crystal Violet (CV), and Malachite Green (MG) are three common representative organic dye molecules, which are commonly used as typical SERS probes to test the Raman performance of substrates. To explore the Raman activity of the nanosheets themselves, the Raman signals of the probe molecules R6G, CV, and MG at three different concentrations on Ti3C2 nanosheets were tested, and the Raman spectra were plotted and analyzed to obtain the enhancement effect of Ti3C2 nanosheets on the probe molecule signals.

[0138] Using the probe molecules R6G, CV, and MG as SERS analytes, standard solutions with different concentrations were prepared, and the Raman signal intensities on Ti3C2 nanosheets were detected in turn. Figure 13 The Raman signals of the three probes, R6G (a), CV (b), and MG (c), on Ti3C2 nanosheets. Figures a, b, and c are the Raman spectra of the R6G, CV, and MG probe molecules at different concentrations (from high to low: 1×10 -6 M, 1×10 -7 M, 1×10 -8 M) on Ti3C2 nanosheets. The Raman characteristic peaks of the probe molecule R6G on Ti3C2 nanosheets are 617 cm -1 、779 cm -1 、1367 cm -1 、1516 cm -1 and 1654 cm -1 , the characteristic peaks of CV are located at 914 cm -1 、1174 cm -1 、1367 cm -1 、1587 cm -1 and 1618 cm -1 , the characteristic peaks of MG are located at 1219 cm -1 、1368 cm -1 and 1615 cm -1 , and the lowest concentration at which R6G, CV, and MG signals can be detected on T i3 C2 nanosheets is 1×10 -8 M.

[0139] Spectral test results of probe molecules R6G, CV, and MG with three different concentrations on Ti3C2 nanosheets showed that the positions of the typical Raman characteristic peaks of R6G, CV, and MG shifted. The reason for the peak shift is related to the charge properties of the nanosheets and the probe molecules. All three probe molecules are cationic fluorescent probes, while the surfaces of the two types of nanosheets etched with a mixed solution of LiF and HCl carry anionic functional groups, and the nanosheet solutions are negatively charged. Briefly speaking, electrons transfer from the anionic MXene nanosheets to the cationic dyes, and a charge transfer (CT) process in the chemical enhancement mechanism occurs between the nanosheet surface and the probe molecules, resulting in the Raman characteristic peak shift phenomenon.

[0140] In addition, the signal intensity of R6G is more prominent on the nanosheet substrate than that of the other two probe molecules. In the present invention, the lowest detectable concentration of R6G by Ti3C2 nanosheets is one order of magnitude lower than that of CV and MG, and the figure shows that the Raman signal intensity of R6G at each concentration (1×10 -6 M~1×10 -8 M) on Ti3C2 is stronger than that of CV and MG at the same concentration. This may be related to the molecular structure of R6G, which is different from the other two probes. The charge transfer interaction between R6G and MXene among the three probe molecules is stronger, so the Raman signal enhancement effect of MXene on R6G is slightly higher than that of CV and MG. In addition, the Raman laser wavelength used in the present invention is 532 nm, the light absorption peak of CV is 591 nm, the light absorption peak of MG is 663 nm, while the light absorption peak of R6G is 527 nm, which is closer to the excitation light wavelength of 532 nm. Therefore, the signal intensity of R6G on the nanosheet is higher than that of CV and MG.

[0141] From the spectral test results of the probe molecules R6G, CV, and MG on the two types of nanosheets, the nanosheets themselves have a certain signal enhancement effect on the probe molecules. The detection limit of the R6G signal can reach 1×10 -8 M, which shows an obvious gap compared with other two-dimensional materials. After analysis, the main reasons are as follows: MXene nanosheets themselves have plasma resonance characteristics and show good SERS properties, and the chemically etched nanosheets carry anionic surface termination functional groups, which are exactly opposite to the cations carried by the probe molecules, resulting in an extremely easy charge transfer phenomenon between the two, which also exactly conforms to the chemical mechanism reasons for enhancing SERS signals.

[0142] 3. Determination of plasticizers in methanol solution by Ti3C2-PDDA-Au@AgNPs SERS sensor

[0143] When initially exploring the detection effect of the Ti3C2-PDDA-Au@AgNPs sensor on PAEs, the present invention selected two of the most common plasticizers, DMP and DEHP, as the research objects. The high-concentration DMP and DEHP standard solutions were successively diluted with chromatographic methanol into low-concentration solutions (1×10 -6 M to 1×10 -14 M). Under the same experimental conditions, the SERS spectra of different concentrations of DMP and DEHP methanol standard solutions on the Ti3C2-PDDA-Au@AgNPs sensor were tested.

[0144] Figure 14 SERS spectra of DMP and DEHP methanol standard solutions on the sensor are shown. As can be seen from Figure 14 a and c therein, the Raman characteristic peaks of DMP and DEHP are mainly concentrated between 1100 cm -1 and 1700 cm -1 . Among them, the Raman characteristic peak signals at 1145 cm -1 , 1271 cm -1 and 1494 cm -1 for DMP, and at 1149 cm -1 , 1273 cm -1 and 1496 cm -1 for DEHP are more obvious. The present invention takes the SERS signals of DMP and DEHP at the typical characteristic peaks as the reference objects and observes that the signal intensities of the characteristic peaks of DMP at these three positions show a decreasing trend with the decrease of the standard solution concentration, and the same trend exists in DEHP. When the concentrations of the DMP and DEHP standard solutions are reduced to 1×10 -13 M, repeated experiments show that under the optimal experimental conditions, obvious Raman characteristic peak signals can still be detected on the sensor, and the detection limits (LOD) of the Ti3C2-PDDA-Au@AgNPs sensor for the plasticizer DMP and DEHP methanol standard solutions are determined to be 1×10 -13 M.

[0145] In addition, to further analyze the variation relationship between the PAEs standard solution concentration and the SERS signal, as shown in Figure 14 b, with the SERS signal intensity at 1271 cm -1 for DMP as the ordinate and -LogC DMP as the abscissa, the standard curve equation plotted is Y = 31687 - 2367X, and substituting the data to calculate the linear correlation coefficient R 2 = 0.9928; as shown in Figure 14 d, with the characteristic peak signal at 1273 cm -1 shift for DEHP as the ordinate and -LogCDEHP The standard curve equation plotted with the abscissa is Y = 55783 - 4185X. Substituting the data for calculation gives the linear correlation coefficient R 2 = 0.9962. The detection range of this method is 1×10 -6 M~1×10 -13 M.

[0146] According to the SERS spectral results of DMP and DEHP, the LOD of the sensor constructed in the present invention for both PAEs standard solutions is as low as 1×10 -13 M. After calculation, it can be obtained that there is a good linear relationship between the SERS signal of the two plasticizers on the sensor and the logarithm of the concentration, and the linear relationship coefficients are both greater than 0.99.

[0147] This further verifies that the Ti3C2-PDDA-Au@AgNPs sensor has a good SERS enhancement effect on the plasticizer signal, and also lays a good prerequisite for detecting plasticizer PAEs in actual samples by surface-enhanced Raman scattering method.

[0148] 4. Determination of DMP and DEHP Contents in Oils

[0149] Before exploring the experiment of determining plasticizers in the actual sample oil by the Ti3C2-PDDA-Au@AgNPs sensor, the present invention has proved that it has achieved high sensitivity for plasticizers in methanol standard solution, indicating the feasibility of using this sensor to determine plasticizers in real samples by surface-enhanced Raman scattering method. According to the method in (6), the plasticizer extraction experiment was carried out on the sample peanut oil to obtain DMP and DEHP sample solutions with different concentrations (1×10 -9 M, 1×10 -10 M, 1×10 -11 M, 1×10 -12 M, 1×10 -13 M), and the SERS spectra of PAEs on the sensor were respectively tested.

[0150] Figure 15 To determine the plasticizers DMP and DEHP in the actual sample oil by the sensor, in Figure a, the characteristic peaks of plasticizer DMP at 1145 cm -1 , 1271 cm -1 , 1492 cm -1 were specifically analyzed. In Figure c, the characteristic peaks of DEHP at 1148 cm -1 , 1273 cm -1 , 1495 cm -1 were used as reference objects for analysis. It was found that DMP and DEHP were in the range of 10 -9 M - 10 -12SERS signals can be detected within the range of M. Repeated experiments confirmed that the limit of detection (LOD) of the sensor for PAEs in actual peanut oil samples was as low as 1×10 -12 M, demonstrating that the sensor still has high sensitivity for the detection of plasticizers in actual samples.

[0151] To further explore the relationship between the SERS signal intensity of plasticizer PAEs and the sample concentration, it was observed from Figure a and Figure c that the SERS spectral signal of DMP at 1271 cm -1 was the strongest, and the characteristic peak of DEHP at 1273 cm -1 had the most obvious change in amplitude. Therefore, in Figure b, the characteristic peak signal of DMP at 1271 cm -1 shift was used as the ordinate, and -LogC DMP was used as the abscissa to plot the standard curve equation Y = 19413 - 1414X, with a linear correlation coefficient R 2 = 0.9997. In Figure d, the characteristic peak signal of DEHP at 1273 cm -1 shift was used as the ordinate, and -LogC DEHP was used as the abscissa to plot the standard curve equation Y = 37785 - 2857X, with a linear correlation coefficient R 2 = 0.9932, proving that there is a good linear regression relationship between the characteristic peak signal intensity of DMP and DEHP in the actual peanut oil sample and the logarithm of the sample concentration. The detection concentration range of the method is 1×10 -9 M~1×10 -12 M. At the three concentration levels of 1×10 - 9 M, 1×10 -10 M, and 1×10 -11 M, the addition recovery experiments were carried out. The average recovery rate of DMP was 82%, and that of DEHP was 91%.

[0152] Two actual samples of plasticizers were selected for detection to repeatedly verify the feasibility of the sensor of the present invention in application. By comparing the test results of the standard solutions and actual sample solutions of plasticizers DMP and DEHP on the sensor, it was found that the lowest LOD of the sensor for the two actual sample solutions was one order of magnitude higher than that of the standard solution, and at the same concentration, the SERS signal of the plasticizer actual sample solution at the typical characteristic peak was lower than that of the standard solution, which may be related to other mixed components in peanut oil.

[0153] Although the substances present in the actual sample have a certain interference effect on the detection of plasticizers in surface-enhanced Raman scattering spectroscopy tests, the sensor can still achieve the detection of low concentrations of 1×10 -12The plasticizer sample solution of M was subjected to SERS test, and the characteristic peaks of the plasticizer can also be clearly distinguished from a series of spectra, indicating that the sensor of the present invention has achieved high-sensitivity identification in actual sample detection.

[0154] The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A preparation method of a Ti3C2-PDDA-Au@AgNPs composite substrate material, characterized in that, It includes the following steps: Drop the poly(diallyldimethylammonium chloride) solution into the Ti3C2 nanosheet solution, stir at room temperature, centrifuge to discard the supernatant, wash the obtained precipitate, and then redisperse it in deionized water to obtain a positively charged Ti3C2 nanosheet solution; Add the positively charged Ti3C2 nanosheet solution to the Au@AgNPs solution, stir, centrifuge to discard the supernatant, wash the obtained precipitate, and then redisperse it in deionized water to obtain a Ti3C2-PDDA-Au@AgNPs composite substrate material.

2. The preparation method of the Ti3C2-PDDA-Au@AgNPs composite substrate material according to claim 1, wherein The preparation process of the Ti3C2 nanosheet solution includes the following steps: Add lithium fluoride to the hydrochloric acid solution, heat and stir, then add the Ti3AlC2 precursor, continue to heat and stir, centrifuge to discard the supernatant, wash the obtained precipitate until it is neutral, and after the precipitate shows a swelling phenomenon, redisperse the obtained precipitate in deionized water, ultrasonicate and centrifuge in an ice bath to obtain a dark green supernatant, that is, the Ti3C2 nanosheet solution.

3. The preparation method of the Ti3C2-PDDA-Au@AgNPs composite substrate material according to claim 2, characterized in that, During the preparation of the positively charged Ti3C2 nanosheet solution: The volume ratio of the Ti3C2 nanosheet solution to the poly(diallyldimethylammonium chloride) solution is 15∶0.5; The conditions for centrifugation are: Centrifuge at 3500 rpm for 1 h.

4. The preparation method of the Ti3C2-PDDA-Au@AgNPs composite substrate material according to claim 1, wherein, The preparation method of the Au@AgNPs solution includes the following steps: Mix the HAuCl4·4H2O solution with deionized water and heat it in an oil bath until the solution is slightly boiling. After adding the sodium citrate solution under stirring, keep the solution slightly boiling until it changes from colorless to purple-red, cool it naturally to room temperature, and filter to obtain the AuNPs solution; Add ascorbic acid to the AuNPs solution, stir at room temperature, then add silver nitrate solution, and continue to stir at room temperature until the solution changes from purple-red to orange-yellow, and filter to obtain the Au@AgNPs solution.

5. The preparation method of the Ti3C2-PDDA-Au@AgNPs composite substrate material according to claim 1, wherein, During the preparation of the Ti3C2-PDDA-Au@AgNPs composite substrate material: The volume ratio of the Au@AgNPs solution to the positively charged Ti3C2 nanosheet solution is 6∶0.5; and / or The conditions for centrifugation are: Centrifuge at 4000 rpm for 20 min.

6. A Ti3C2-PDDA-Au@AgNPs composite substrate material prepared by using the preparation method according to any one of claims 1-5.

7. A SERS sensor, characterized in that, Using the Ti3C2-PDDA-Au@AgNPs composite substrate material according to claim 6 as a carrier and a cationic dye as a probe molecule.

8. The SERS sensor according to claim 7, wherein The cationic dye includes one of rhodamine 6G, crystal violet, and malachite green.

9. An application of the SERS sensor according to any one of claims 7-8 in the field of plasticizer detection.

10. A method for detecting plasticizers in oils and fats, characterized in that, Detect the plasticizer in grease by using the SERS sensor according to any one of claims 7-8.

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