Preparation method of SERS (Surface Enhanced Raman Scattering) substrate based on Ag NPs / Au NWs / FP composite material and application of SERS substrate in detection of abietic acid

Abstract

The invention discloses a preparation method of an SERS (Surface Enhanced Raman Scattering) substrate based on an Ag NPs / Au NWs / FP composite material and an application of the SERS substrate in abietic acid detection, and the preparation method is characterized by comprising the following steps: cutting filter paper into uniform small pieces, then sequentially cleaning the small pieces with ethanol and water under an ultrasonic condition, drying the small pieces of FP, immersing the small pieces of FP in a gold nanoparticle solution for 5 minutes to 3 hours, and cleaning and drying to obtain Au NPs / FP; mixing the Au NPs / FP with ethanol, an ethanol solution of 4-MBA, a HAuCl4 solution and an L-ascorbic acid solution, and standing at room temperature to obtain Au NWs / FP; ag NPs is uniformly deposited on the surface of Au NWs / FP through a magnetron sputtering method, the SERS substrate based on the Ag NPs / Au NWs / FP composite material is obtained, and the SERS substrate based on the Ag NPs / Au NWs / FP composite material has the advantages that SERS sensitivity and detection stability can be enhanced, and high-precision quantitative analysis of abietic acid can be achieved.

Description

Technical Field

[0001] This invention relates to a SERS substrate, and more particularly to a method for preparing a SERS substrate based on Ag NPs / Au NWs / FP composite material and its application in the detection of rosin acid. Background Technology

[0002] Abietic acid (AA), also known as abietic acid, is a natural tricyclic diterpenoid compound and the main component of rosin. AA's unique phenanthrene ring skeleton, carbon-carbon double bonds, and carboxylic acid groups give it excellent preservative, moisture-proof, adhesive, and emulsifying properties. Rosin is used as a sizing agent in paper food packaging materials to improve the water resistance and strength of paper products. However, toxicological studies have shown that abietic acid poses certain health risks to humans. It is a skin and lung sensitizer; long-term or repeated contact can lead to allergic skin reactions, lysis of alveolar epithelial cells, toxicity to red blood cells and polymorphonuclear leukocytes, and effects on the central nervous and respiratory systems, potentially even leading to death in severe cases. During use, sizing agents such as abietic acid can migrate from paper cups and bowls, contaminating food and posing a risk to consumer health. Therefore, a convenient and efficient method for detecting AA is urgently needed to monitor the abietic acid content in the relevant food environment in real time, thereby accurately assessing food safety.

[0003] Conventional methods for the qualitative and quantitative determination of abietic acid include high-performance liquid chromatography (HPLC), gas chromatography-spectroscopy, and ultra-high-performance liquid chromatography-tandem mass spectrometry (UPLC-MS / MS). While these methods offer good separation and sensitivity, they also have drawbacks such as demanding instrumentation requirements, high operator skill levels, high cost, and long detection times. The fat-soluble and volatile nature of abietic acid means its content in food systems varies over time and space; therefore, traditional methods are insufficient for real-time detection of abietic acid content.

[0004] Surface-enhanced Raman spectroscopy (SERS), as a non-destructive technique, has demonstrated unique advantages in the qualitative and quantitative detection and dynamic monitoring of trace target substances due to its rapid response and high sensitivity. Therefore, a simple, rapid, and sensitive new method for detecting amino acid (AA) residues in food is proposed. Finally, this method is applied to the real-time monitoring of the migration patterns of AA during the use of commercially available coated paper cups for beverages. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing a SERS substrate based on Ag NPs / Au NWs / FP composite material that can enhance the sensitivity and detection stability of SERS and its application in the detection of rosin acid, which can realize high-precision quantitative analysis of rosin acid.

[0006] The technical solution adopted by this invention to solve the above-mentioned technical problems is: a method for preparing a SERS substrate based on Ag NPs / Au NWs / FP composite material, characterized by comprising the following steps: Step 1, Preparation of Au NPs / FPs: The filter paper was cut into uniform small pieces, and then cleaned with ethanol and water under ultrasonic conditions. The small FP pieces were dried in a constant temperature oven at 30-40 ℃. The FP pieces were then immersed in a gold nanoparticle solution for 5 min-3 h, cleaned with water and ethanol, and dried in a fume hood at 30-40 ℃ to obtain Au NPs / FP. Step 2, Magnetron sputtering deposition of Ag NPs: The Au NPs / FP obtained in step 1 were mixed with ethanol, 10 mM 4-MBA ethanol solution, 17 mg / mL HAuCl4 solution and 1.54 mg / mL L-ascorbic acid solution, and placed at room temperature for 20-60 min to obtain Au NWs / FP; Ag NPs were uniformly deposited on the surface of Au NWs / FP by magnetron sputtering for 5-12 s to obtain a SERS substrate based on Ag NPs / Au NWs / FP composite material.

[0007] Further, the synthesis method of the gold nanoparticles described in step 1 is as follows: 19.7 μL of HAuCl4 with a concentration of 100 mg / mL and 100 μL of sodium citrate with a concentration of 14.7 mg / mL are added to 20 mL of water. The mixed solution changes from light yellow to colorless. Then, 600 μL of ice-cold NaBH4 solution with a concentration of 3.783 mg / mL is added to the beaker, and the mixture is stirred for 5-15 min. Finally, it is allowed to stand for 1-3 h to obtain stable Au nanoparticles.

[0008] Furthermore, the FP sheet described in step 1 is immersed in the gold nanoparticle solution for 1 hour.

[0009] Further, the volume ratio of the ethanol, the 10 mM 4-MBA ethanol solution, the 17 mg / mL HAuCl4 solution, and the 1.54 mg / mL L-ascorbic acid solution in step 2 is 100:20:5:30.

[0010] Furthermore, the sputtering time in step 2 is 10 seconds.

[0011] Furthermore, the magnetron sputtering method described in step 2 uses a sputtering power of 80W, argon gas purity of 99.999%, a target spacing of 10cm, and a base vacuum of 8×10⁻⁶. -4 Pa, working pressure 7.5 Pa.

[0012] The present invention also provides the application of the SERS substrate prepared by the above method in the quantitative detection of rosin acid by SERS.

[0013] Furthermore, the method for using the SERS substrate to detect the content of rosin acid in a solid-phase coated paper cup is as follows: After soaking the coated paper cup in ethanol solution at 90°C for 12 h, 20 μL of ethanol solution containing rosin acid is dropped onto the back of the SERS substrate based on Ag NPs / Au NWs / FP composite material, and SERS detection is performed directly to determine the content of rosin acid in the ethanol solution.

[0014] Furthermore, the method for using the SERS substrate to detect the content of rosin acid in beer is as follows: 20 μL of beer solution containing rosin acid is dropped onto the back of the SERS substrate based on Ag NPs / Au NWs / FP composite material, and the content of rosin acid in the beer solution is determined directly by SERS detection.

[0015] Compared with the prior art, the advantages of the present invention are: 1. Innovative Substrate Structure: The Ag NPs / Au NWs / FP flexible substrate provides a high-density electromagnetic "hot spot" through the jungle-like array of Au NWs, which, combined with the near-field coupling effect of Ag NPs, significantly enhances the SERS signal intensity; the hydrophilicity and impurity filtration capability of the filter paper allow for direct extraction of AA from complex food matrices without pretreatment, achieving a detection sensitivity of 10×10⁻⁶. -9 M.

[0016] 2. Multi-scenario detection capability: This method can simultaneously determine the total AA content in coated paper cups (with an error of <5.8% compared to HPLC detection) and the amount of dynamic migration, and predict the safe drinking window (e.g., within 1 hour for hot drinks and within 6 hours for cold drinks) based on a temperature-time coupling model, providing full-cycle monitoring for food packaging safety.

[0017] In summary, this invention provides a method for preparing a SERS substrate based on Ag NPs / Au NWs / FP composite materials and its application in detecting rosin acid. This method can monitor the changes in AA content in coated paper cups in real time during solid phase (packaging materials), liquid phase (beverages), and dynamic migration processes. Furthermore, it guides safe usage standards through a temperature-time dependent migration model, providing technical support for the risk control of rosin acid migration in food packaging. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the preparation and detection process for Ag NPs / Au NWs / FP substrates; Figure 2 In the image, (a) is a macroscopic SEM image of Au seed / FP, (b) is a microscopic SEM image of Au seed / FP, and (c) is a SEM image of FP. Figure 3 (a) is a macroscopic SEM image of Au NWs / FP, and (b) is a microscopic SEM image of Au NWs / FP. Figure 4 (a) is a macroscopic SEM image of Ag NPs / Au NWs / FP, and (b) is a microscopic SEM image of Ag NPs / Au NWs / FP. Figure 5 SEM images of Au NWs prepared from gold nanoparticles with different adsorption times, where (a) 5 min, (b) 30 min, (c) 1 h, and (d) 3 h; Figure 6 UV-Vis absorption spectra of Ag NPs / Au NWs / FP sputtered for different durations; Figure 7 (a) shows the CV SERS signals obtained on FP, Au NWs / FP, Ag NPs / FP, and Ag NPs / Au NWs / FP; (b) shows the CV SERS signals obtained on FP, Au NWs / FP, Ag NPs / FP, and Ag NPs / Au NWs / FP at 1624 cm⁻¹. -1 The corresponding intensity at that location; Figure 8 In the middle, (a) shows the SERS signals of different concentrations of CV, and (b) shows the semi-log quantitative fitting curve of the CV SERS signal; Figure 9 CV SERS signals measured at 1624 cm⁻¹ for five batches of Ag NPs / Au NWs / FP substrates -1 Signal strength at the location; Figure 10 A scatter plot of the SERS intensity mapping (2500 points) for CV molecules; Figure 11 (a) is an illustration of the Raman spectrum and molecular structure of AA; (b) is a PCA plot of the SERS spectra of AA at different concentrations. Figure 12 SERS signals for different concentrations of AA in beer; Figure 13 The amount of AA migration at different temperatures and durations. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0020] I. Reagents and Instruments Reagents: Sodium citrate (C6H5Na3O7, 99.8%) and sodium borohydride (NaBH4) were purchased from Sigma-Aldrich. Chloroauric acid (HAuCl4·xH2O, 99.9%), 3-aminopropyltriethoxysilane (APTES, 99%), 4-mercaptobenzoic acid (4-MBA, 90%), and acetonitrile (CH3CN, >99%) were purchased from Aladdin. Methanol and ethanol were purchased from Macklin Biochemical Co., Ltd. L-ascorbic acid (L-AA) and crystal violet (CV) were provided by Sinopharm Chemical Reagent Co., Ltd. Arisin acid (AA) standard was provided by Beijing Mannheimer Biotechnology Co., Ltd. Filter paper with a pore size of 15-20 µm (FP) was purchased from Jiangsu Taizhou Aoke Filter Paper Factory. All chemical reagents used were of analytical grade, and the water used was deionized water (18.2 MΩ·cm).

[0021] Instrumentation: AA extraction was performed using an IKA Vortex circular oscillator (3 Shaker, Germany) and a Scientz ultrasonic cleaner (SB25-12DTD, China). High-performance liquid chromatography (HPLC) analysis was performed using an Agilent 1260 HPLC system (Agilent Technologies, USA). Morphological images of the substrate were acquired using a field emission scanning electron microscope (SEM, SU-70, Hitachi, secondary electron mode) at an accelerating voltage of 5 kV. The proportions and distributions of each element were characterized using energy-dispersive X-ray spectroscopy (EDS, EDAXTEAM Apollo XL) and elemental mapping. The crystal structure of the substrate was studied using an X-ray power diffractometer (D8 ADVANCE, Bruker) equipped with a Cu-Kα radiation source in the range of 5–60° (2θ). Ultraviolet-visible (UV-Vis) spectra were obtained using a TU-1901 UV-Vis spectrometer (Pgeneral). All SERS signals were measured using a Raman spectrometer (Ocean Optics, QE Pro) equipped with a ProSp-Micro40-VIS system, with an integration time of 10 s, a laser wavelength of 532 nm, and a power of 1 mW.

[0022] Specific Embodiment 1: A method for preparing a SERS substrate based on Ag NPs / Au NWs / FP composite material, such as... Figure 1 As shown, it includes the following steps: Step 1, Preparation of Au NPs / FPs: Filter paper (FP) was cut into uniform pieces of 0.5 cm × 0.5 cm. The pieces were then cleaned sequentially with ethanol and water under ultrasonic conditions for 2 h. After drying in a 37 ℃ incubator, the FP pieces were immersed in 5 mL of nanoparticle solution for 1 h. All samples were then washed with water and ethanol, and finally dried in a fume hood at 37 ℃ to obtain Au NPs / FP. The surface structure of Au NPs / FP is shown below. Figure 2 As shown in (a), with Figure 2 (c) The similarity of the FP morphology diagrams indicates that the adsorption of Au nanoparticles does not change the surface morphology of FP. Figure 2 The statistical results in (b) show that after FP was fully immersed in the gold nanoparticle solution, gold nanoparticles with an average diameter of 25.9 ± 7.6 nm were uniformly adsorbed on its surface.

[0023] The above-mentioned gold nanoparticles were synthesized using the sodium citrate reduction method: 19.7 μL of HAuCl4 with a concentration of 100 mg / mL and 100 μL of sodium citrate with a concentration of 14.7 mg / mL were added to 20 mL of water. The mixed solution changed from light yellow to colorless. Then, 600 μL of ice-cold NaBH4 solution with a concentration of 3.783 mg / mL was added to the beaker, stirred for 10 min, and finally allowed to stand for 2 h to obtain stable Au nanoparticles (abbreviated as Au NPs), which were stored at 4 ℃ for later use. Step 2, Magnetron sputtering deposition of Ag NPs: In a clean beaker, 1 mL of ethanol, 200 µL of 10 mM 4-MBA ethanol solution, 50 µL of 17 mg / mL HAuCl4 solution, and the Au NPs / FP prepared in step 1 were added sequentially. Finally, 300 μL of 1.54 mg / mL L-ascorbic acid (L-AA) was added, and the mixture was left to stand at room temperature for 40 min to obtain gold nanowires / FP (abbreviated as Au NWs / FP). The surface structure of Au NWs / FP is as follows. Figure 3 As shown in (a), compared with Au NPs / FP ( Figure 2 Compared to (a), the surface wrinkles are reduced and the flatness is increased, indicating a more stable interfacial bonding between Au NWs and the flexible substrate, and the interfacial adhesion of Au NWs / FP may be stronger. The unique morphology of Au NWs is as follows: Figure 3As shown in (b), due to the unique ligand properties of 4-MBA, the gold wires of Au NWs exhibit a high aspect ratio and longitudinal extension, making it possible to form a jungle-like Au NWs array. Furthermore, the average diameter of the gold wires is 34.1 ± 6.9 nm, which is larger than the average diameter of the gold nanoparticles, increasing the effective contact between the EM "hot spots" and the target molecules entering the gaps, thus triggering a better SERS signal. Ag NPs were deposited on the surface of gold nanowires / FPs by magnetron sputtering at a sputtering power of 80 W, argon purity of 99.999%, a target spacing of 10 cm, and a base vacuum of 8 × 10⁻⁶. -4 AgNPs were uniformly deposited on the substrate surface by DC sputtering at a working pressure of 7.5 Pa for 10 s, resulting in an AgNPs / Au NWs / FP substrate. The surface structure of AgNPs / Au NWs / FP is shown below. Figure 4 (a) Figure 4 As shown in (b), the wrinkles on the FP surface are further covered, and the smoothness is enhanced. This indicates that AgNPs effectively fill the gaps in the Au NWs network, forming a more continuous surface coverage and further suppressing interfacial stress concentration. After Ag NPs fill the gaps in Au NWs, they enhance the connectivity of the conductive network and can significantly reduce surface resistance (Ag has a higher conductivity than Au), making it more suitable for flexible electrode applications. Ag NPs are uniformly distributed on the clustered Au NWs, retaining the original microstructure and structure of the nanowire array, but with subtle changes, and the gold wires are more unidirectional. This forest-like structure with a large specific surface area can provide more adsorption sites, and the dense nanowire array structure can also generate more Raman "hot spots".

[0024] Optimization of fabrication conditions for Ag NPs / Au NWs / FP flexible substrates prepared in Specific Example 2 and Specific Example 1 1. Optimization of adsorption time: The adsorption time of Au nanoparticles has a significant impact on the morphology and SERS performance of Au NWs. To determine the optimal adsorption time, four experimental groups were set up for 5 min, 30 min, 1 h, and 3 h.

[0025] Figure 5 (a) When the attachment time is 5 min, Au nanoparticles cannot be effectively loaded onto the filter paper surface, resulting in the interruption of nanowire growth and the formation of only sporadic Au nanoparticles. Figure 5 (b) When the adsorption time was 30 min, the density of Au NWs decreased significantly, the average diameter increased, and the surface showed a sparse short-branched structure. Figure 5 (c) When the attachment time is 1h, Au NWs exhibit a vertically arranged jungle-like structure with high surface roughness; Figure 5(d) When the adsorption time was extended to 3 h, excessive growth of Au NWs led to the accumulation of wire clusters, a decrease in surface roughness, and a reduction in the density of electromagnetic "hot spots". Ultimately, 1 h was selected as the optimal adsorption time.

[0026] 2. Splash duration optimization: To investigate the effect of Ag NPs on the final SERS signal, different sputtering durations ranging from 5 s to 12 s were set during substrate preparation. Figure 6 As shown, with increasing sputtering time, the absorption of Au NWs gradually weakens, and the intensity of the absorption characteristic peaks originally belonging to Au NWs decreases significantly, the peak shape broadens, and they are weakened into shoulder peaks. These changes may be due to the increased coverage of Ag NPs reducing the exposed area of ​​Au NWs. Considering the stability of Ag NPs, a sputtering time of 10 s, which has high Ag NP coverage and also allows the properties of Au NWs to be manifested, yields the best SERS performance for the flexible substrate.

[0027] 3. Synergistic effect of Ag NPs and Au NWs The CV SERS signals of FP, Au NWs / FP, Ag NPs / FP, and Ag NPs / Au NWs / FP were measured, and the results are as follows: Figure 7 As shown in (a) and (b), the SERS performance of multi-component composite substrates composed of Ag NPs and Au NWs with FP is further enhanced compared to single substrates. Comparative analysis reveals that Ag NPs play a dominant role in enhancing the SERS signal. However, the enhancing effect of Au NWs cannot be ignored; its unique structure provides abundant tips and corresponding "hot spots" for the EM effect, and its brush-like structure facilitates molecular enrichment, ultimately contributing to better SERS detection.

[0028] The above Ag NPs / FP were prepared by directly sputtering Ag NPs onto FP using magnetron sputtering technology for 10 s.

[0029] Performance analysis of the Ag NPs / Au NWs / FP flexible substrate prepared in Specific Example 3 and Specific Example 1.

[0030] 1. The capabilities of Ag NPs / Au NWs / FP substrates in trace substance analysis The ability of the prepared Ag NPs / Au NWs / FP substrate in trace analysis was evaluated using gradient concentration CV solutions. The SERS signal results of CV are shown below. Figure 8 As shown in (a). In 10 -8 M to 10 -3Within the M range, the substrate exhibited a stable SERS signal with robust enhancement, demonstrating the stability and superiority of the prepared Ag NPs / Au NWs / FP substrate in trace substance detection. Semi-logarithmic quantitative fitting was performed on the obtained CV SERS signal to obtain... Figure 8 As shown in curve (b), the gradient concentration of the CV solution exhibits a good linear relationship with the SERS signal, R 2 The value of 0.996 indicates that the substrate performs excellently in micro-detection and has a good SERS enhancement effect. The calculated limit of detection (LOD) for CV is 9.09 × 10⁻⁶. -10 M indicates that the Ag NPs / Au NWs / FP substrate has excellent low-concentration detection capability.

[0031] 2. Repeatability analysis: Five different batches of Ag NPs / Au NWs / FP substrates were prepared, and 10 SERS spectra from each batch were randomly selected (a total of 50 spectra). Figure 9 As shown, at 1624 cm -1 Using the characteristic peak intensity as an indicator, the batch-to-batch relative standard deviation (RSD) was calculated, and the result was 11.12%, indicating that the substrate preparation process has good reproducibility. The substrate preparation process is stable (RSD < 12%), and the surface SERS activity is uniformly distributed, ensuring reliable detection results.

[0032] 3. Uniformity Analysis A 10 × 10 μm² region was randomly selected on the substrate surface, and SERS signals were acquired at 2500 sites with a step size of 0.2 μm. Analysis was performed on a 1624 cm⁻¹ area. -1 The distribution of signal strength is calculated, and the relative standard deviation (RSD) of signal strength within the region is determined. For example... Figure 10 As shown, the RSD of the SERS signal intensity at 2500 detection sites was 11.4%, confirming the uniform distribution of SERS activity on the substrate surface. This SERS method outperforms traditional HPLC techniques in terms of sensitivity, stability, and applicability, providing an efficient tool for studying the migration patterns of amino acids (AA) in food packaging materials.

[0033] Specific Example 4: The Ag NPs / Au NWs / FP substrate prepared based on Specific Example 1 is used for SERS quantitative detection of AA in solid phase (packaging material).

[0034] Eight types of coated paper cups (abbreviated as LPCs) were randomly collected from the market and soaked in 250 mL of ethanol solution at 90℃ for 12 h. The content of AA in the ethanol solution was then determined by the SERS detection method of this invention and the traditional HPLC method.

[0035] Record some basic parameters of the purchased paper cups, including thickness, density, and LDPE layer thickness. The thickness of these paper cups ranges from 181 to 282 μm, and their density ranges from 0.868 to 0.950 g·cm³. -3 The thickness of the LDPE film ranged from 8 to 20 μm, as shown in Table 1. This indicates that there may be significant differences in film thickness among paper cups with similar functions, and these physical properties may determine the total amount and release potential of the sizing agent AA. Comparing the test results of each group, it was found that paper cups with thicker LDPE films had higher AA concentrations but lower migration rates. This may be because the use of more sizing agent increased the AA concentration, but LDPH had poor permeability to AA leaching and a relatively stronger inhibitory effect.

[0036] Table 1 Basic parameters of coated paper cups

[0037] Table 2 Total AA content in coated paper cups

[0038] The total AA content in paper cups was determined using both SERS and HPLC methods, and the results are shown in Table 2. Comparing the two methods, the SERS detection model based on the Ag NPs / Au NWs / FP substrate showed almost the same accuracy as HPLC, with errors ranging from -0.2% to 5.8%. This indicates that the SERS detection model based on this substrate performed well, had acceptable accuracy, and can effectively perform qualitative and quantitative detection of AA in the food environment.

[0039] Specific Example 5: The Ag NPs / Au NWs / FP substrate prepared based on Specific Example 1 is used for SERS quantitative detection of AA in liquid.

[0040] like Figure 11 As shown in figure a, the Raman spectrum of rosin acid (abbreviated as AA) at 711 cm⁻¹ -1 The scattering peak at 1198 cm⁻¹ is mainly related to the skeletal vibrations of AA; -1 The peak at 1434 cm⁻¹ is attributed to the stretching vibration of the C-C; -1 The peak at 1647 cm⁻¹ is simultaneously generated by the deformation vibration of CH in CH₂ and CH₃, the stretching vibration of CO in COOH, and the coupling of COOH-CH₃. -1 The strongest spectral peak at this location corresponds to the stretching vibration of the C=C conjugate bond in AA. This demonstrates that the developed Ag NPs / Au NWs / FP substrate can perform SERS detection of AA molecules in a food environment.

[0041] 20 μL of beer solutions containing different concentrations of AA (10 -3 ~10 -8.5 M) were dropped onto the back side of a flexible substrate containing Ag NPs / Au NWs / FP, and SERS was directly performed. As the concentration of AA in the beer solution decreased, the intensity of the SERS response showed a monotonically decreasing trend, but still exhibited stable characteristic peaks. PCA technology was used to analyze the SERS spectra of different AA concentrations, such as... Figure 11 As shown in (b). The PCA plot reveals significant differences between datasets with different AA concentrations. -8 M and 10 -8.5 Significant differences exist in the M-spectral dataset.

[0042] like Figure 12 As shown, the intensity of the SERS response decreases monotonically with decreasing AA concentration in the beer solution, but still exhibits stable characteristic peaks. Therefore, this substrate can be used for ultra-trace (at least down to 10) AA molecules in beer. -8.5 M) detection: This technology has the dual capability of qualitative identification (characteristic peaks) and potential quantitative analysis (intensity changes with concentration) of AA in food. It exhibits high sensitivity and selectivity, and the substrate performs excellently in real, complex food environments (beer), effectively resisting matrix interference.

[0043] Specific Example 6: Raman detection method for real-time monitoring of AA migration based on Ag NPs / Au NWs / FP substrate prepared in Specific Example 1.

[0044] The migration of AA (acetic acid) in coated paper cups (LPCs) during use was monitored in real time using an Ag NPs / Au NWs / FP substrate combined with SERS technology. The maximum migration amount of AA within the test time was determined using the ethanol immersion method. LPCs were immersed in 250 mL of ethanol solution at 90 °C for 12 h, and the content of AA after migration was then determined using SERS. The results are shown in Table 3. AA migration was observed in all groups of solutions, with migration rates ranging from 57.18% to 68.42%, indicating that AA migration is a common phenomenon during the use of LPCs.

[0045] Table 3 Maximum migration of AA

[0046] According to GB 31604.1-2015 standard, the migration patterns of rosin acid (AA) in coated paper cups (LPCs) at different temperatures (5℃, 20℃, 40℃, and 70℃) were simulated. The experiments showed that significant AA migration was observed in all temperature groups, with a final migration saturation of approximately 93%. Furthermore, the higher the temperature, the faster the migration rate (reaching saturation fastest at 70℃). Figure 13 It was found that when the AA migration reached 20%, a turning point in the migration rate occurred in all groups. This suggests that due to the initial low AA content in the LDPE layer, the increased porosity within the layer over time accelerates the release of AA between the laminate and the paperboard. Based on the dynamic migration model, the recommended safe drinking time limits are: ≤1 hour for hot drinks at 70℃, ≤2.5 hours at 40℃, ≤4.5 hours at 20℃, and ≤6 hours for cold drinks at 5℃. This aims to control the AA migration ratio below the safe threshold of 20%, significantly reducing the migration risk. The research results provide a scientific basis for the rational use of coated paper cups.

[0047] The foregoing description is not intended to limit the invention, nor is the invention limited to the examples given. Any changes, modifications, additions, or substitutions made by those skilled in the art within the scope of the invention should also be considered within the protection scope of the invention.

Claims

1. A method for preparing a SERS substrate based on Ag NPs / Au NWs / FP composite material, characterized in that, Includes the following steps: Step 1, Preparation of Au NPs / FP: Cut the filter paper into uniform small pieces, then clean it with ethanol and water under ultrasonic conditions, dry the small FP pieces in a constant temperature oven at 30-40 ℃, immerse the FP pieces in gold nanoparticle solution for 5 min-3 h, clean them with water and ethanol, and dry them in a fume hood at 30-40 ℃ to obtain Au NPs / FP; Step 2, Magnetron sputtering deposition of Ag NPs: The Au NPs / FP obtained in Step 1 were mixed with ethanol, 10 mM 4-MBA ethanol solution, 17 mg / mL HAuCl4 solution and 1.54 mg / mL L-ascorbic acid solution, and placed at room temperature for 20-60 min to obtain Au NWs / FP; Ag NPs were uniformly deposited on the surface of Au NWs / FP by magnetron sputtering for 5-12 s to obtain a SERS substrate based on Ag NPs / Au NWs / FP composite material.

2. The method for preparing a SERS substrate based on Ag NPs / Au NWs / FP composite material according to claim 1, characterized in that, The synthesis method of gold nanoparticles described in step 1 is as follows: 19.7 μL of HAuCl4 with a concentration of 100 mg / mL and 100 μL of sodium citrate with a concentration of 14.7 mg / mL are added to 20 mL of water. The mixed solution changes from light yellow to colorless. Then, 600 μL of ice-cold NaBH4 solution with a concentration of 3.783 mg / mL is added to the beaker, and the mixture is stirred for 5-15 min. Finally, it is allowed to stand for 1-3 h to obtain stable Au nanoparticles.

3. The method for preparing a SERS substrate based on Ag NPs / Au NWs / FP composite material according to claim 1, characterized in that, The FP sheet described in step 1 is immersed in the gold nanoparticle solution for 1 hour.

4. The method for preparing a SERS substrate based on Ag NPs / Au NWs / FP composite material according to claim 1, characterized in that, The volume ratio of the ethanol, the 10 mM 4-MBA ethanol solution, the 17 mg / mL HAuCl4 solution, and the 1.54 mg / mL L-ascorbic acid solution in step 2 is 100:20:5:

30.

5. The method for preparing a SERS substrate based on Ag NPs / Au NWs / FP composite material according to claim 1, characterized in that, The sputtering time in step 2 is 10 seconds.

6. The method for preparing a SERS substrate based on Ag NPs / Au NWs / FP composite material according to claim 1, characterized in that, The magnetron sputtering method described in step 2 uses a sputtering power of 80W, argon gas purity of 99.999%, a target spacing of 10cm, and a base vacuum of 8×10⁻⁶. -4 Pa, working pressure 7.5 Pa.

7. The application of the SERS substrate prepared by the method of any one of claims 1-6 in the quantitative detection of rosin acid by SERS.

8. The application according to claim 7, characterized in that... The method for using the SERS substrate to detect the content of rosin acid in a solid-phase coated paper cup is as follows: After soaking the coated paper cup in ethanol solution at 90℃ for 12 h, 20 μL of ethanol solution containing rosin acid is dropped onto the back of the SERS substrate based on Ag NPs / Au NWs / FP composite material, and SERS detection is performed directly to determine the content of rosin acid in the ethanol solution.

9. The application according to claim 7, characterized in that... The method for using the SERS substrate to detect the content of rosin acid in beer is as follows: 20 μL of beer solution containing rosin acid is dropped onto the back of the SERS substrate based on Ag NPs / Au NWs / FP composite material, and the content of rosin acid in the beer solution is determined directly by SERS detection.

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