A method for detecting contamination in three-phase samples based on aerogel three-dimensional SERS

Abstract

This invention relates to the field of sensing and detection technology, specifically to a three-phase sample contamination inspection method based on aerogel three-dimensional SERS. Using cassava starch (CS) as the supporting structure and CDS as the reducing agent, silver-loaded starch aerogel (ACA) was prepared by freeze-drying (sol-gel method). The changes in the spacing of AgNPs on the aerogel surface before and after collapse were characterized by SEM and TEM, demonstrating the increase in SERS hotspots. The functional group changes and elemental composition of ACA during synthesis were characterized by FTIR and XPS. The adsorption isotherm and kinetics of ACA were studied using BET. In practical applications, this invention successfully utilized the high specific surface area and high adsorption capacity of ACA to successfully detect gaseous 4-ATP. Furthermore, leveraging the collapse property, trace detection of solid and liquid TBZ was achieved on and within apples.

Description

Technical Field

[0001] This invention relates to the field of sensing and detection technology, specifically to a method for detecting contamination in three-phase samples based on aerogel three-dimensional SERS. Background Technology

[0002] Surface-enhanced Raman spectroscopy (SERS) is a fast-response, non-destructive, real-time, and ultrasensitive detection technique that can also reflect the chemical fingerprint information of analytes. Currently, there are two main explanations for the SERS enhancement principle: electromagnetic enhancement (EM) and chemical enhancement (CM). The EM mode enhances the signal based on distance rather than chemical properties, providing the same SERS effect for various target molecules. However, a dramatic SERS enhancement only occurs when the probe molecule is less than 5 nm from the surface of noble metal nanoparticles. Therefore, researchers refer to the location of the high-intensity electric field between noble metal nanoparticles as a "hot spot." When a probe molecule is within a "hot spot," its SERS signal is dramatically enhanced. Three-dimensional structures that increase the specific surface area to adsorb more analyte molecules and thus improve the SERS "hot spot" distribution density are frequently developed. Over the past few decades, various SERS substrates have been developed, including one-dimensional (1D) nanowires, two-dimensional (2D) planar arrays, and three-dimensional (3D) porous networks. The maximum number of SERS "hot spots" in 1D and 2D substrates is limited to a single Cartesian plane. However, in 3D SERS substrates, the spatial expansion along the z-axis dimension results in a larger total surface area. Due to the increased specific surface area (SSA), more "hot spots" can be obtained from low-dimensional SERS to high-dimensional SERS, thus achieving higher detection sensitivity. Furthermore, compared to 1D and 2D substrates, 3D substrates exhibit better light source utilization efficiency because they do not require precise laser focusing and can fully utilize scattered light.

[0003] Aerogels, with their low density, controllable macroscopic shapes, and diverse pore structures, are ideal plasmonic metal nanoparticle loading frameworks for SERS substrates. Importantly, on the one hand, the 3D structure of aerogels can increase the number of "hot spots" along the x, y, and z axes. On the other hand, the ultra-high specific surface area and internal 3D network structure of aerogels can facilitate the capture of target molecules.

[0004] However, after analytes are introduced into aerogels, they typically accumulate within the aerogel itself. Since SERS is a surface-based sensing technique, most SERS measurements using aerogels as a substrate are performed on the aerogel surface, making it difficult to detect SERS performance in areas with higher analyte concentrations. The utilization rate of aerogel "hot spots" is also limited to the aerogel surface, without a true increase in the number of "hot spots." If, after loading analytes, the concentration of both "hot spots" and analytes continues to increase—for example, through aerogel collapse—the number of "hot spots" on the aerogel surface will increase, resulting in stronger SERS performance and significantly improved SERS sensitivity. Sandeep Surendra Panikar et al. used cellulose nanocrystals (CNCs) to form aerogels loaded with AuNPs, and then utilized aerogel collapse to achieve sensitive detection of organophosphorus pesticides in rice and tea extracts. However, its synthesis process is relatively complex, and its possibility of industrialization and mass production is low. Furthermore, the detection methods are limited to analytes with deionized water as the solvent. However, most harmful substances such as antibiotics and pesticides are poorly soluble in water, which greatly affects the SERS detection of actual samples. Summary of the Invention

[0005] The purpose of this invention is to provide a three-phase sample contamination inspection method based on aerogel three-dimensional SERS, which utilizes the high hydrophilicity, porosity, high specific surface area and ultra-low density of starch aerogel to perform rapid and accurate SERS quantitative analysis of contaminants in the gas phase, liquid phase and solid phase.

[0006] To achieve the above objectives, this invention provides a method for detecting contamination in three-phase samples based on aerogel three-dimensional SERS, comprising the following steps:

[0007] Step 1: Synthesize the reducing agent dialdehyde starch using cassava starch as raw material;

[0008] Step 2: Prepare silver-loaded, highly hydrophilic starch aerogel as the SERS substrate;

[0009] Step 3: Select SERS probe molecules for sample detection and obtain SERS spectra;

[0010] Step 4: Perform gas-liquid-solid three-phase detection.

[0011] Optionally, the execution process of step 1 is as follows: using cassava starch as raw material and sodium periodate as oxidant, the 2,3-o-dihydroxy group of cassava starch is selectively oxidized to an aldehyde group; 0.2g of cassava starch and 0.2g of sodium periodate are placed in a 100mL beaker, 20mL of deionized water is added, and after thorough stirring, sulfuric acid is added dropwise to maintain the pH of the system at 3.0. The reaction is carried out at room temperature in the dark for 5 hours; after the reaction is completed, the white solid produced is separated by centrifugation; then the solid is suspended in deionized water and centrifuged again. This step is repeated 3 to 5 times until the supernatant is no longer tested with starch-potassium iodide test paper and no iodate or sulfuric acid is found in the supernatant, and the solution is neutral. The product is freeze-dried for 12 hours, taken out and ground to obtain the product dialdehyde starch.

[0012] Optionally, during step 2, 0.2 g of cassava starch and 0.2 g of sodium periodate were placed in a 100 mL beaker and reacted to obtain dialdehyde starch with a dialdehyde molar fraction of 80.76%. A certain mass of cassava starch and 0.1 g of dialdehyde starch were mixed, 10 mL of deionized water was added, and the mixture was heated until gelatinized. A certain volume of Tollens' reagent was added, and after reacting for 5 min, the resulting sol was dropped into a 96-well plate using a pipette. The plate was then set and refluxed at 2-4 °C for 12 h, and finally freeze-dried to obtain the SERS-based silver-loaded hydrophilic starch aerogel.

[0013] Optionally, during step 3, the organic dyes rhodamine 6G and crystal violet were selected as probe molecules for SERS. 50 μL of different concentrations of rhodamine 6G and crystal violet were dropped onto the surface of silver-loaded hydrophilic starch aerogel, and dried at 80 °C for 10 min after collapsing. The optimal SERS substrate was detected using a laser confocal micro Raman spectroscopy instrument with a laser wavelength of 532 nm, an exposure time of 1 s, and a power of 10%, to obtain all SERS spectra.

[0014] Optionally, in step 4, the gas phase detection utilizes the porosity of the silver-loaded, highly hydrophilic starch aerogel to absorb the harmful gas p-aminothiophenol; the solid phase detection is performed in situ on the apple surface; and the liquid phase detection uses the standard addition method to determine the recovery rate of the apple juice sample.

[0015] This invention provides a three-phase sample contamination detection method based on three-dimensional SERS of aerogels. Using cassava starch (CS) as the supporting structure and CDS as the reducing agent, silver-loaded starch aerogels (ACA) were prepared by freeze-drying. The changes in the spacing of AgNPs on the aerogel surface before and after collapse were characterized by SEM and TEM, demonstrating the increase in SERS hotspots. The functional group changes and elemental composition of ACA during synthesis were characterized by FTIR and XPS. The adsorption isotherm and kinetics of ACA were studied using BET. In practical applications, this invention successfully utilized the high specific surface area and high adsorption capacity of ACA to detect gaseous 4-ATP. Furthermore, leveraging the collapse property, trace detection of solid and liquid TBZ was achieved on and within apples. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic flowchart of a three-phase sample contamination inspection method based on aerogel three-dimensional SERS according to the present invention.

[0018] Figure 2 These are the corresponding spectra of ACA, cassava starch (CS), dialdehyde starch (CDS), and starch aerogel (CA) in embodiments of the present invention.

[0019] Figure 2 a is a comparison chart of UV-Vis.

[0020] Figure 2 b is an FTIR comparison chart.

[0021] Figure 2 c is the XPS spectrum of ACA.

[0022] Figure 2 d is the high-resolution spectrum.

[0023] Figure 3 This is a schematic diagram of SEM (ad) and TEM (ef) analysis of ACA in an embodiment of the present invention.

[0024] Figure 4 This is a schematic diagram illustrating the characteristics of the ACA in an embodiment of the present invention.

[0025] Figure 4 a is a schematic diagram of particle size distribution.

[0026] Figure 4 b is the XRD pattern.

[0027] Figure 4 c is a schematic diagram of the N2 adsorption isotherm and the BJH pore size distribution curve.

[0028] Figure 4 d is a schematic diagram showing the change in height of the ACA before and after the collapse.

[0029] Figure 5 These are Raman spectra and standard curves of different concentrations of R6G and CV on substrates ACA(ad), ATA(ef), and APA(gh) in embodiments of the present invention.

[0030] Figure 6 This is a schematic diagram of the SERS performance of ACA in this embodiment of the invention, showing repeatability (ab), reproducibility (cd), and stability (e).

[0031] Figure 7 This is a schematic diagram showing the SERS and standard curve of gas-solid-liquid three-phase detection of ACA in this embodiment of the invention, and the influence of different substances in apples on TBZ. Detailed Implementation

[0032] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0033] Explanation of English abbreviations used in the text:

[0034] SERS: Surface-enhanced Raman spectroscopy;

[0035] CS: Tapioca starch;

[0036] CDS: Dialdehyde starch;

[0037] ACA: Silver-loaded starch aerogel;

[0038] CA: Starch aerogel;

[0039] 4-ATP: p-Aminothiophenol.

[0040] EM: Electromagnetic Enhancement

[0041] CM: Chemical Enhancement

[0042] TBZ: Thiabendazole

[0043] SEM: Scanning Electron Microscopy

[0044] TEM: Transmission electron microscopy

[0045] FTIR: Fourier Transform Infrared Absorption Spectrometer

[0046] XPS: X-ray photoelectron spectroscopy

[0047] BET: Specific Surface Area Test Method

[0048] XRD: X-ray diffraction

[0049] CV: Crystal Violet

[0050] R6G: Rhodamine 6G

[0051] ATA: Silver-loaded potato starch aerogel

[0052] APA: Silver-loaded pea starch aerogel

[0053] UV-Vis: Ultraviolet-Vis spectrum

[0054] Please see Figure 1 This invention provides a method for detecting contamination in three-phase samples based on aerogel three-dimensional SERS, comprising the following steps:

[0055] S1: Dialdehyde starch, a reducing agent, is synthesized from cassava starch.

[0056] S2: Preparation of silver-loaded, highly hydrophilic starch aerogel as a SERS substrate;

[0057] S3: Select SERS probe molecules for sample detection to obtain SERS spectra;

[0058] S4: Perform gas-liquid-solid three-phase detection.

[0059] The following description, in conjunction with specific embodiments and execution steps, provides further details:

[0060] (1) Synthesis of reducing agent CDS

[0061] 0.2 g of CS and 0.2 g of sodium periodate were placed in a 100 mL beaker, and 20 mL of deionized water was added. After thorough stirring, sulfuric acid (1 M) was added dropwise to maintain the pH of the system at 3.0. The reaction was carried out at room temperature in the dark for 5 hours. After the reaction was completed, the white solid produced was separated by centrifugation. The solid was then suspended in deionized water and centrifuged again. This step was repeated 3 to 5 times until the supernatant was free of iodate or sulfuric acid and the solution was neutral, as tested with starch-potassium iodide paper. The product was then freeze-dried for 12 hours, ground, and the product CDS was obtained.

[0062] (2) Synthesis of base ACA

[0063] 0.2 g of CS and 0.2 g of sodium periodate were reacted in a 100 mL beaker to obtain CDS with a dialdehyde molar fraction of 80.76%. A certain mass of CS and 0.1 g of CDS were mixed, 10 mL of deionized water was added, and the mixture was heated until gelatinized. A certain volume of Tollens' reagent was added dropwise, and the reaction was allowed to proceed for 5 min. The resulting sol was then pipetted onto a 96-well plate and allowed to set and reflux at 2-4 °C for 12 h. Finally, the plate was freeze-dried to obtain the SERS-based ACA.

[0064] The synthesis of ACA utilizes the unique gelatinization and retrogradation properties of starch. Starch is mainly composed of amylose and amylopectin. During gelatinization, starch granules absorb water and swell, and the starch molecular chains extend and intertwine in a double helix to form a gel network. After low-temperature storage, the hydrogen bonds between adjacent molecules gradually form dense starch molecular bundles, which is the hydrogel. After freeze-drying, the hydrogel forms an aerogel with a three-dimensional network structure with uniform pores. Aerogels are prepared by mixing bis(aldehyde) starch (CDS) and tapioca starch (CS), where CS serves as the supporting structure and CDS acts as a reducing agent to reduce AgNPs. The experimental procedure involves first mixing and gelatinizing CS and CDS in different ratios (6:1, 5:1, 4:1, 3:1, 2:1), then adding 1 ml of Tollens' reagent. The resulting sol is then dropped into a 96-well plate and set and retrograded at 2-4℃ for 12 hours. Finally, after freeze-drying for 24 hours, ACA is obtained.

[0065] Specifically, Figure 2 a) is the UV-Vis spectrum of the silver-loaded starch aerogel (ACA). Under light, ACA exhibits surface plasmon resonance, thereby enhancing the local electromagnetic field intensity near the particle surface, with a UV absorption peak appearing at 420 nm. In contrast, CA, CDS, and CS show no significant absorption peaks in the 300-800 nm range. (In the FTIR spectrum...) Figure 2 b) The aldehyde group in the CDS is at 1735 cm⁻¹ -1 The absorption peak generated at [specific location] did not appear in ACA, indicating that the aldehyde group may have participated in the chemical reaction. CS and cassava starch aerogel (CA) were not significantly different, suggesting that the chemical structure of CS did not change considerably before and after gelatinization. Figure 2 The cd spectrum represents the full and fine spectra of ACA. The full spectrum consists of the assigned peaks of elements such as Ag, C, O, and N, while the fine spectrum shows the characteristic peaks of Ag 3d5 / 2 and Ag 3d3 / 2 at 367.4 eV and 373.4 eV, respectively. Combined XPS, FTIR, and UV-Vis analyses confirmed the successful formation and loading of Ag NPs onto the surface of starch aerogel.

[0066] The surface morphology of the prepared ACA before and after collapse is as follows: Figure 3 As shown in the diagram, prior to the collapse, ACA exhibited a well-defined three-dimensional porous structure. Figure 3 a) After collapse, the three-dimensional porous structure of the aerogel disappears, forming a dense plane. Figure 3 b). As the aerogel collapses, the Ag NPs loaded on its surface gradually move closer to each other, and the resulting SERS hotspots also gradually increase. Figure 3 cd).

[0067] In addition, TEM analysis was performed. Figure 3 e) First, the image clearly shows that the reaction forms typical silver nanospheres. Then, TEM was used to determine the particle size distribution of the nanoparticles loaded on the aerogel. The obtained TEM images were analyzed using NanoMeasurer 1.2 software to calculate the average size distribution of approximately 100 particles and plot it as a histogram, as shown below. Figure 4 (a) The synthesized Ag NPs have a particle size of approximately 16.1 nm. In the XRD pattern ( Figure 4 (b) Cassava starch exhibits four distinct diffraction peaks at 15.1°, 17.9°, 18.1°, and 23.1°, characteristic of a typical type A crystal structure. The CA diffraction pattern shows no peaks, exhibiting characteristics similar to an amorphous structure, with a significantly reduced relative crystallinity. This is due to the destruction of the granular structure of cassava starch at high temperatures, resulting in the disappearance of the crystal structure. The peaks at 38.2°, 44.4°, 64.6°, and 77.6° correspond to planes (111), (200), (220), and (311), respectively, consistent with data from PDF#87-0720. This further confirms the growth of AgNPs on the aerogel surface.

[0068] Finally, the BET specific surface area and porous structure of CA and ACA were characterized by N2 adsorption-desorption analysis. Figure 4 c shows the N2 adsorption isotherms and BJH pore size distribution curves for CA and ACA (inset). In the low-pressure stage, N2 molecules are adsorbed on the inner surface of ACA in monolayer to multilayer configurations, indicating the presence of a certain amount of micropores. In the high-pressure stage, the desorption and adsorption isotherms do not coincide, indicating that the adsorption behavior is caused by the macropores in the aerogel. According to the six types of adsorption-desorption isotherms classified by the International Union of Pure and Applied Chemistry (IUPAC), the N2 adsorption-desorption isotherm of starch aerogel belongs to type IV and forms a hysteresis loop, indicating a hierarchical pore size distribution in the aerogel. The specific surface areas of CA and ACA are 4.387 m² / s². 2 / g and 1.400m 2 / g, the decrease in specific surface area may be due to the adsorption of Ag NPs on the aerogel.

[0069] To test the water sensitivity of ACA, approximately 50 μL of the analyte solution (aqueous solution) was dropped onto the surface of the ACA and then dried at 80°C for 5 min. Figure 4 In diagram d, the height of the ACA before collapse was approximately 0.33 cm, and the thickness of the ACA after collapse was approximately 0.13 mm, indicating that the collapse effect of the ACA was good.

[0070] (3) Sample preparation and SERS measurement

[0071] To evaluate the sensitivity, stability, repeatability, and reproducibility of the SERS substrate ACA, this patent selected the organic dyes rhodamine 6G (R6G) and crystal violet (CV) as SERS probe molecules. 50 μL of different concentrations of R6G and CV were dropped onto the surface of the aerogel, allowed to collapse, and then dried at 80°C for 10 min. The optimal SERS substrate was detected using laser confocal microRaman spectroscopy, with a laser wavelength of 532 nm, an exposure time of 1 s, and 10% power, yielding all SERS spectra.

[0072] The SERS performance of ACA mainly includes its quantitative detection capability, stability, repeatability, and reproducibility. Firstly, the quantitative detection of ACA was studied. Figure 5 a, c show the interaction between ACA and different concentrations of R6G (10) -5 -10 -10 M) and CV(10 -5 -10- 10 M) SERS spectrum after mixed collapse. R6G and CV at 614 cm⁻¹ -1 and 1622cm -1 The Raman intensity at 614 cm⁻¹ decreased significantly with decreasing concentration. -1 and 1622cm -1 A linear relationship was established between SERS intensity and the concentrations of R6G and CV. Figure 5 b, d), the results show that there is a good linear relationship between the two (y = 0.442x + 7.18 and y = 0.433x + 7.26) and the correlation coefficient (R) is high. 2 The values ​​were 0.996 and 0.997, respectively. Therefore, highly sensitive and wide-range quantitative analysis of R6G and CV can be achieved.

[0073] Secondly, the quantitative detection capabilities of ATA and APA were examined. Experimental results showed that ATA had a higher sensitivity for R6G detection than APA (…). Figure 5This is likely due to the presence of numerous pores in the substrate after the APA collapse. The linear relationships between ATA and APA with respect to R6G are y = 0.507x + 7.54 and y = 0.526x + 7.50, respectively, and the correlation coefficients (R...) 2 The values ​​are 0.991 and 0.980, respectively.

[0074] Finally, the stability, repeatability, and reproducibility of ACA were studied. Differences in SERS intensity at different sampling locations on the same substrate were compared, such as... Figure 6 a. Randomly select 20 points on the substrate to measure 10 -6 The SERS intensity of MR6G is relatively uniform. The characteristic peak is at 614 cm⁻¹. -1 The relative standard deviation (RSD) of the strength at each location was 5.5%. Figure 6 b) and SERS imaging was performed at the characteristic peak of 614 cm⁻¹. Figure 6 c). Both indicate that the substrate has good repeatability. Five different batches of ACA were selected for 10... -6 The spectrum of MR6G, RSD( Figure 6 d) The reproducibility was 3.5%, demonstrating that the substrate has good reproducibility. Comparisons of the same batch of ACA at different times were performed using R6G (10⁻⁶ M), such as... Figure 6 e. The SERS properties of the material were measured every 30 days, with R6G at its characteristic peak at 614 cm⁻¹. -1 The strength did not change significantly, indicating that the substrate's stability is also relatively good.

[0075] (4) Gas-liquid-solid three-phase detection

[0076] The gas detection utilizes the porosity of aerogel (ACA) to absorb the harmful gas p-aminothiophenol (4-ATP). This paper employs the Long-kun Yang method to generate gaseous 4-ATP molecules. A certain volume of 4-ATP alcohol solution was added to a beaker and heated to 80°C. Simultaneously, ACA was adhered to a glass slide with double-sided tape, inverted onto the beaker, and sealed with plastic wrap to achieve adsorption equilibrium of gaseous 4-ATP within the beaker. 50 μL of deionized water was dropped onto the ACA surface to cause the aerogel to collapse. After drying for 10 min, SERS detection was performed.

[0077] To date, gas-phase SERS detection remains extremely challenging due to the low affinity of airborne species for metal surfaces. ACA, with its large specific surface area before collapse and high-density "hot spots" after collapse, presents an ideal solution for gas-phase SERS detection. In a sealed beaker, ACA reached gas-phase 4-ATP adsorption equilibrium while water was dripped and collapsed, followed by further SERS measurements. Thirty spectra were measured at different concentrations (200 mg / L, 100 mg / L, 50 mg / L, 10 mg / L, 5 mg / L, 1 mg / L). Figure 7 ab shows representative SERS spectra of 4-ATP at different concentrations from 200 mg / L to 1 mg / L, and ACA at 1075 cm⁻¹ in the concentration range of 50 mg / L to 1 mg / L. -1 The equation shows a good linear relationship (y = 5438.2x + 160.6) and a correlation coefficient (R²). 2 The LOD (Limit of Detection) was 0.996. This reliable gas detection demonstrates the unique advantages of ACA over traditional noble metal aggregates. The LOD was calculated using LOD = 3Sb / M, where Sb is the standard deviation of the SERS intensity of the blank sample at the characteristic peak, and M is the slope of the plotted calibration curve. The calculated LOD was 0.64 mg / L. ACA exhibits exceptional SERS stability in air. Unlike traditional SERS substrates, this stable substrate in aerogel form is easy to store and use, facilitating on-site SERS applications such as rapid and reliable gas detection chemical analysis, food safety inspections, and counter-terrorism.

[0078] Solid-phase detection was performed in situ on the apple surface. First, a standard curve of TBZ at different concentrations (50 mg / L, 10 mg / L, 5 mg / L, 1 mg / L, 0.5 mg / L, 0.25 mg / L, 0.1 mg / L) was established in a methanol solution. Next, 1 mL of TBZ at different concentrations (10 mg / L, 5 mg / L, 1 mg / L) was sprayed onto the apple surface using a syringe to simulate pesticide residues. The solution was left overnight to allow the methanol to evaporate. Finally, 50 μL of methanol was dropped onto the surface of the ACA (Alternative Acid) solution and used to wipe the surface of the positive apple. After drying at 80°C for 1 min to allow the methanol to evaporate, 50 μL of deionized water was added to cause the solution to collapse. The solution was then dried for 10 min before SERS measurements were performed.

[0079] In practical applications, swab sampling is considered the most widely used sampling and portable analytical method for surface contamination. To evaluate the practical application of ACA's SERS, thiabendazole was used as the test probe molecule. TBZ, a systemic benzimidazole fungicide and parasite cleaner, is widely used in agricultural products to prevent rot and wilt caused by fungal infection during transportation and long-term storage of vegetables and fruits. Generally, TBZ is less toxic than other pesticides, but high doses can still lead to thyroid hormone imbalance and liver damage. The U.S. Environmental Protection Agency (EPA) has classified it as a carcinogen. TBZ can be used for fruit preservation in a strictly controlled manner, with the maximum usage limited to 20 mg / L. Therefore, the development of sensitive and rapid site detection methods is particularly urgent.

[0080] Detailed ACA swab testing is as follows: Quantitative detection of different concentrations (50 mg / L, 10 mg / L, 5 mg / L, 1 mg / L, 0.5 mg / L, 0.25 mg / L, 0.1 mg / L) of TBZ in methanol solution was performed using substrate ACA. The intensity of the SERS spectrum decreased as the TBZ concentration decreased from 50 ppm to 0 ppm. Figure 7 c), which indicates that TBZ concentration is positively correlated with SERS spectral intensity. Figure 7 d is at 781cm -1 The linear relationship between the SERS intensity of the characteristic peak and the logarithm of the TBZ concentration is expressed by the quantitative equation y = 2524.3x + 1231.6, with a correlation coefficient R0. 2 =0.979 and LOD is 0.053 mg / L. Therefore, the SERS spectral intensity can be used for the quantitative analysis of TBZ in methanol solution.

[0081] To verify the accuracy and reliability of the SERS substrate ACA, 10 mg / L, 5 mg / L, and 1 mg / L TBZ were dropped onto the surface of apples, incubated overnight, and then wiped with ACA filled with methanol. The recovery rate of the spiked TBZ was studied. The recovery rate of TBZ was 95.0%–99.4%, demonstrating good food safety detection performance. In addition, SERS measurements were performed on other concentrations used for fitting (50 mg / L, 0.5 mg / L, 0.25 mg / L, and 0.1 mg / L). Figure 7 e is at 781cm -1 The linear relationship between the SERS intensity of the TBZ characteristic peak on the apple surface and the logarithm of the TBZ concentration was established by the quantitative equation y = 2406.7x + 2521.6, with a correlation coefficient R0. 2 =0.980 and LOD is 0.067 mg / L.

[0082] Liquid phase detection is a relatively traditional method and is consistent with the methods for solid phase detection and establishing standard curves. The recovery rate of apple juice samples was determined using the standard addition method. 3 mL of TBZ at different concentrations (50 mg / L, 10 mg / L, 5 mg / L, 1 mg / L, 0.5 mg / L, 0.25 mg / L, 0.1 mg / L) was mixed with 1 mL of apple juice, followed by the addition of 1 mL of 1% acetonitrile. The mixture was stirred thoroughly, then 0.4 g of MgSO4 and 0.17 g of CH3COONa were added. The mixture was centrifuged at 8000 rpm for 5 min. 50 μL of the supernatant was dropped onto the surface of ACA and dried at 80 °C for 5 min until the organic solvent acetonitrile evaporated. Then, 50 μL of deionized water was added to cause the mixture to collapse, and it was dried for 10 min. Finally, SERS measurements were performed.

[0083] The lowest concentration of TBZ in actual samples was investigated. SERS tests were performed on TBZ in the range of 0.1–50 mg / L. When the TBZ concentration was below 0.1 mg / L, 781 cm⁻¹ -1 and 1009cm -1 Characteristic peaks are not easily identified. Figure 7 FG recorded the SERS spectra of different concentrations (50 mg / L, 10 mg / L, 5 mg / L, 1 mg / L, 0.5 mg / L, 0.25 mg / L, 0.1 mg / L) of TBZ in apple juice samples. A sample without TBZ was used as a control. After adding TBZ, as the concentration of TBZ decreased, the SERS spectra at 781 cm⁻¹ were observed. -1 The intensity of the characteristic SERS peak that appears will also decrease accordingly. In apple juice, 781 cm⁻¹ -1 The standard curve at point R is y = 2538.7x + 2522.4. 2 The value is 0.987, and the calculated LOD is 0.063 mg / L. Therefore, this method can reliably identify positive simulated samples.

[0084] Furthermore, the embodiments investigated the anti-interference performance and selectivity of the method of the present invention. Inorganic and organic substances that may coexist in apple juice were selected, including Ca... + K + Mg + Na + Cl - Vitamin C, thiram, and acetamiprid. (For example...) Figure 7 As shown in h, when these substances are used as interfering agents, the TBZ is at 781 cm⁻¹. -1 The SERS signal change rate at the location was less than 4.8%, indicating that the substances that may coexist in the actual sample have little interference with thiabendazole and that ACA has good selectivity for thiabendazole, proving that this method can be used to detect thiabendazole residues in apple juice.

[0085] In summary, this invention successfully detected gaseous 4-ATP by utilizing the high specific surface area and high adsorption capacity of ACA, and achieved trace detection of solid and liquid TBZ on the surface and inside apples by utilizing the collapse property. This method opens up broad possibilities for the application of SERS in food safety and environmental safety;

[0086] The analysis of gas-liquid-solid three-phase substances using p-aminothiophenol (4-ATP) and thiabendazole verified the practical application of ACA as a gas-liquid-solid three-phase detection material. The synthesized multifunctional integrated material ACA has great potential in SERS applications. Starch-based SERS substrates possess advantages such as low pollution, high cost-effectiveness of raw materials, simple preparation methods, and good biocompatibility, creating limitless possibilities for the application of novel SERS substrates in various fields.

[0087] The above description discloses only one preferred embodiment of the present invention, and should not be construed as limiting the scope of the present invention. Those skilled in the art will understand that all or part of the processes of the above embodiments can be implemented, and equivalent changes made in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A three-phase sample contamination checking method based on aerogel three-dimensional SERS, characterized in that, The method comprises the following steps: Step 1: synthesizing a reducing agent, dialdehyde starch, by using cassava starch as a raw material; In the execution process of step 1, 2,3-o-dihydroxyl of cassava starch is selectively oxidized into an aldehyde group by using sodium periodate as an oxidizing agent; 0.2 g of cassava starch and 0.2 g of sodium periodate are taken in a 100 mL beaker, 20 mL of deionized water is added, and after being fully stirred, sulfuric acid is added dropwise to keep the pH of the system at 3.0, and the reaction is carried out at room temperature for 5 h in the dark; after the reaction is completed, the white solid produced is separated by centrifugal separation; then the solid is suspended in deionized water and centrifuged again, and this step is repeated 3 to 5 times until there is no iodate or sulfuric acid in the upper clear liquid detected by starch-potassium iodide test paper, and the solution is neutral; the product is freeze-dried for 12 h, ground, and dialdehyde starch with a dialdehyde molar fraction of 80.76% is obtained; Step 2: preparing a silver-loaded high-hydrophilic starch aerogel as a SERS substrate; In the execution process of step 2, a certain mass of cassava starch and 0.1 g of dialdehyde starch are mixed, 10 mL of deionized water is added and heated to gelatinize, a certain volume of Tollens reagent is added dropwise, and after reacting for 5 min, the sol formed is dropped into a 96-well plate for shaping and rebirth at 2-4℃ for 12 h, and finally freeze-dried to obtain the silver-loaded high-hydrophilic starch aerogel as a SERS substrate; Step 3: selecting a probe molecule for SERS sample detection to obtain a SERS spectrum; In the execution process of step 3, organic dyes rhodamine 6G and crystal violet are selected as probe molecules for SERS, 50 μL of rhodamine 6G and crystal violet with different concentrations are dropped on the surface of the silver-loaded high-hydrophilic starch aerogel to make it collapse, and then dried at 80℃ for 10 min; a laser confocal Raman spectrometer is used for sample detection of the SERS substrate, the laser wavelength is selected as 532 nm, the exposure time is 1 s, and the power is 10%, and all SERS spectra are obtained; Step 4: performing gas-liquid-solid three-phase detection.

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