Method for rapidly detecting SO2 by ratio type SERS (Surface Enhanced Raman Scattering) based on headspace sampling

Abstract

The invention discloses a method for rapidly detecting SO2 through ratio type SERS (Surface Enhanced Raman Scattering) based on headspace sampling, and relates to the technical field of gas detection. The method comprises the following steps: S1, preparing an Au-coated Ag-Au-coated AAO substrate; S2, adsorbing SO2; and S3, calculating the residual quantity of SO2. The ratio-type Au (at) Ag-Au (at) AAO substrate provided by the invention can specifically adsorb SO2 gas, display Raman characteristic peaks (613cm <-1 > and 920cm <-1 >) and enhance the Raman signal intensity, internal standard molecules 4-MBA are arranged in Au (at) Ag-Au gaps, random fluctuation of SERS signals can be calibrated, quantitative detection of SO2 is realized through peak value ratio analysis of the SO2 gas characteristic peak (613cm <-1 >) and the internal standard molecule characteristic peak (1078cm <-1 >), and the method has the advantages that the method is simple and convenient to operate, and the application prospect is wide. The method shows a good linear relationship in a detection range of 0.5 mg / kg-500 mg / kg, and can be used for realizing high-sensitivity rapid detection of the residual quantity of SO2 in the traditional Chinese medicinal materials.

Description

Technical Field

[0001] The invention relates to the technical field of gas detection, and in particular to a method for rapid detection of SO2 by ratiometric SERS based on headspace sampling. Background Art

[0002] Gases exist in every aspect of our lives and constantly affect human life. Gas detection is widely used in various fields of industry and life, such as chemical industry, environmental protection, medical treatment, food, transportation, etc., to detect the concentration of combustible, flammable, toxic and harmful gases, components in mixed gases, or disease biomarkers in exhaled breath, etc. With the huge demand for environmental monitoring, food safety and disease diagnosis, the effective sensing of target gases is crucial to human life and public safety;

[0003] Traditional Chinese medicine plays an important role in maintaining health. Sulfur fumigation, as a traditional method of processing Chinese medicine, has the advantages of insect prevention, easy storage and brightness. However, excessive sulfur fumigation will chemically transform the original bioactive ingredients contained in the Chinese medicine itself, thereby changing its clinical efficacy and safety. In addition, the sulfurization process will leave SO2 residues in the Chinese medicine. Excessive intake of SO2 can cause health hazards. Existing sulfite / SO2 detection methods include acid-base titration, chromatography, electrochemistry, capillary electrophoresis, colorimetry and fluorescence spectroscopy. There are shortcomings such as time-consuming extraction steps, low precision, bulky equipment and the need for professional operators. Rapid on-site detection of SO2 residues in Chinese medicine is still a challenge.

[0004] Surface enhanced Raman spectroscopy (SERS) has been widely used to detect trace amounts or even single molecules. As an ultrasensitive, non-destructive molecular sensing tool, SERS technology shows the potential to increase gas detection sensitivity by several orders of magnitude. In recent years, SERS sensors have developed into a powerful tool for on-site detection of SO2 in traditional Chinese medicine due to their simple operation, fast response time, no or minimal sample pretreatment, high sensitivity and high selectivity. However, due to the distribution of "hot spots" and changes in measurement conditions, SERS lacks reproducibility in point-to-point testing. Therefore, accurate and reliable quantitative SERS analysis has proven to be a major challenge for widespread application.

[0005] In view of the above problems, the inventors proposed a method for rapid detection of SO2 by ratiometric SERS based on headspace sampling to solve the above problems. Summary of the invention

[0006] In order to solve the above problems, the purpose of the present invention is to provide a method for rapid detection of SO2 by ratiometric SERS based on headspace sampling.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solution: a method for rapid detection of SO2 by ratiometric SERS based on headspace sampling, comprising the following steps:

[0008] S1. Preparation of Au@Ag-Au@AAO substrate

[0009] Gold nanoparticles were prepared by reducing HAuCl4 with trisodium citrate, and then the gold nanoparticle solution and a mixed solution containing CTAC, H2O, and NaOH were added to a beaker for heating and stirring, and then AgNO3 and a mixed solution containing CTAC, AA, and NaOH were added for reaction. After the reaction was complete, the mixture was cooled to room temperature and centrifuged to obtain Au@Ag NPs. At the same time, Au I Solution, H2O, CTAC, Au@Ag NPs, 4-MBA, AA were mixed by magnetic stirring, so that the internal standard molecule 4-MBA was placed in the gap between the nanoparticles, and then centrifuged to obtain purified 4-MBA-modified Au@Ag NPs, and then Au I The Au@Ag-Au@AAO substrate was prepared by ligand exchange and then dropping the Au@Ag-Au@AAO@AAO substrate on the AAO substrate.

[0010] S2, adsorption of SO2

[0011] The sample to be tested and the extract were added into a centrifuge tube, and the SO2 gas was obtained by the headspace sampling method. The Au@Ag-Au@AAO substrate was used as a solid phase extraction material to adsorb SO2;

[0012] S3. Calculate the residual SO2

[0013] The Au@Ag-Au@AAO substrate was tested using SERS technology to obtain the SERS spectrum data of the sample to be tested, and the residual SO2 in the sample to be tested was calculated based on the standard curve.

[0014] Preferably, in S1, the size of the gold nanoparticles is 15 nm.

[0015] Preferably, in S1, the preparation of Au I The specific steps of the solution are as follows:

[0016] With 100mL of Au I Taking the solution preparation process as an example, 85.5 mL of H2O, 2 mL of 25 nM HAuCl4·3H2O, 2.5 mL of 100 mM NaOH, and 10 mL of 10 mM Na2SO3 were stirred and mixed until colorless.

[0017] Preferably, in S1, the dropwise addition of AuI Solution, the solution volume is 62.5mL.

[0018] Preferably, in S1, the synthesized Au@Ag-Au has an Ag-Au shell thickness of 25 nm and a nanoparticle gap of 23.5 nm.

[0019] Preferably, in S1, the ligand is exchanged, the Au@Ag-Au solution is centrifuged to obtain a lower precipitate and diluted with a PSS solution, shaken and then centrifuged to obtain a lower precipitate, and resuspended with a PSS solution, followed by centrifugal concentration, TSC is added, and after sufficient shaking, the Au@Ag-Au solution is collected by centrifugation to obtain the citrate-encapsulated Au@Ag-Au.

[0020] Preferably, the volume of TSC is 5 mL and the concentration is 5 mM.

[0021] Preferably, in S1, the Au@Ag-Au coated with the citrate layer is dropped onto the entire surface of AAO, and the vacuum filtration time is 1 min.

[0022] Preferably, in S2, the extracting solution is phosphoric acid, the volume percentage concentration of the phosphoric acid is 5%, 2 mL of phosphoric acid is added to every 1 g of the sample to be tested, the extraction temperature of the headspace sampling method is 25-100° C., and the extraction time is 5-30 min.

[0023] Preferably, in S3, the method for drawing the standard curve is as follows:

[0024] Prepare Na2SO3 standard solution, and perform SO2 headspace sampling and SERS detection in the same way. -1 The characteristic Raman peak height of SO2 at 1078 cm -1 A linear regression was performed between the ratio of the characteristic Raman peak heights of 4-MBA and the corresponding SO2 concentration value.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. In the present invention, the ratiometric Au@Ag-Au@AAO substrate provided can specifically adsorb SO2 gas and show Raman characteristic peaks (613cm -1 , 920cm -1 ), while enhancing the Raman signal intensity, an internal standard molecule 4-MBA is set in the Au@Ag-Au gap to calibrate the random fluctuation of the SERS signal. -1 ) and the internal standard molecular characteristic peak (1078cm -1) peak ratio analysis realizes the quantitative detection of SO2, and shows a good linear relationship in the detection range of 0.5mg / kg-500mg / kg, which can be used to realize the high-sensitivity and rapid detection of SO2 residues in traditional Chinese medicines;

[0027] 2. In the present invention, a ratiometric SERS substrate material is designed and prepared, and combined with the headspace sampling technology, the components to be tested are separated from the complex components of Chinese medicinal materials, and a handheld Raman spectrometer device is used. It has high-sensitivity detection capability and simple operation method, and is suitable for on-site rapid detection of sulfite or SO2 in food safety and environmental supervision. In addition, by modifying different surface ligands on the surface of Au@Ag-Au nanoparticles, this method can be extended to the detection of more gases, such as aldehydes, etc., which solves the problems of the prior art of Chinese medicinal materials SO2 residue detection and extraction steps being time-consuming, low-precision, bulky equipment, and requiring professional operators. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 The present invention is a description of the ratiometric SERS sensor scheme for SO2 detection in traditional Chinese medicine.

[0030] Figure 2 Schematic diagram of the Au@Ag-Au@AAO substrate of the present invention ((a) shows the AAO optical image (upper surface) and Au@Ag-Au@AAO (lower surface), (b) shows the SERS signal of the Au@Ag-Au@AAO substrate).

[0031] Figure 3 Scanning electron microscope characterization images of the AAO and Au@Ag-Au@AAO substrates of the present invention (the left side is the SEM of AAO, and the right side is the SEM of Au@Ag-Au@AAO).

[0032] Figure 4 This is the result of the Au@Ag-Au@AAO substrate specificity investigation of the present invention.

[0033] Figure 5 The Raman mapping diagram of the Au@Ag-Au@AAO substrate surface randomly selected to investigate the uniformity (where 100×100μm 2In terms of area, 441 points of Raman mapping of 250 mg / kg SO2 were obtained on the same SERS substrate. (a) is 613 cm -1 Raman mapping of SO2 at 1078 cm -1 Raman mapping of 4-MBA at (c) 613cm -1 / I 1078cm -1 The corresponding Raman map).

[0034] Figure 6 The stability test result of Au@Ag-Au@AAO substrate of the present invention (a) is shown in FIG10 -7 SERS spectra of MR6G over 15 days, (b) 613cm -1 ,I 1078cm -1 ,I 613cm -1 / I 1078cm -1 values ​​greater than 15 days).

[0035] Figure 7 The Au@Ag-Au@AAO substrate synthesis process of the present invention is I Solution volume optimization results; (a) Figure 2 shows the solution containing different amounts of Au I 10% of solution -7 SERS spectra of MR6G on Au@Ag-Au@AAO substrates. (b) Figure MR6G on Au@Ao@AAO substrates with different amounts of Au I 10% of solution -7 Ionization of M R6G on Au@Ag-Au@AAO Substrate 613cm -1 / I 1078cm -1 strength ratio).

[0036] Figure 8 The linear range of SO2 content detected by handheld Raman spectrometer based on Au@Ag-Au@AAO substrate in this invention is investigated. (a) Figure 2 shows the SERS spectra of SO2 at different concentrations of 500-0.25 mg / kg, (b) Figure 3 shows the linear range of SO2 (613 cm -1 ) and 4-MBA(1078cm -1 ) ratio of peak intensity to SO2 concentration).

[0037] Fig. 9 This is a linear fitting relationship diagram of the detection results of SO2 residue in traditional Chinese medicine using the distillation titration method of the present invention and the ratio SERS sensor.

[0038] Fig.10 The figure is a schematic diagram of the detection process of an embodiment of the present invention. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] like Figure 1-10 As shown, the present invention provides a method for rapid detection of SO2 based on ratiometric SERS of headspace sampling, comprising the following steps:

[0041] S1. Preparation of Au@Ag-Au@AAO substrate

[0042] Gold nanoparticles were prepared by reducing HAuCl4 with trisodium citrate, and then the gold nanoparticle solution and a mixed solution containing CTAC, H2O, and NaOH were added to a beaker for heating and stirring, and then AgNO3 and a mixed solution containing CTAC, AA, and NaOH were added for reaction. After the reaction was complete, the mixture was cooled to room temperature and centrifuged to obtain Au@Ag NPs. At the same time, Au I Solution, H2O, CTAC, Au@Ag NPs, 4-MBA, AA were mixed by magnetic stirring, so that the internal standard molecule 4-MBA was placed in the gap between the nanoparticles, and then centrifuged to obtain purified 4-MBA-modified Au@Ag NPs, and then Au I The Au@Ag-Au@AAO substrate was prepared by ligand exchange and then dropping the Au@Ag-Au@AAO@AAO substrate on the AAO substrate.

[0043] S2, adsorption of SO2

[0044] The sample to be tested and the extract were added into a centrifuge tube, and the SO2 gas was obtained by the headspace sampling method. The Au@Ag-Au@AAO substrate was used as a solid phase extraction material to adsorb SO2;

[0045] S3. Calculate the residual SO2

[0046] The Au@Ag-Au@AAO substrate was tested using SERS technology to obtain the SERS spectrum data of the sample to be tested, and the residual SO2 in the sample to be tested was calculated based on the standard curve.

[0047] In S1, Au@Ag-Au@AAO substrate was prepared as solid phase extraction material, and SO2 molecules were evaporated from the solution to SO3 2- However, CTAC forms a steric barrier on the surface of Au@Ag-Au nanospheres, which hinders SO3 2- After adsorption, the citrate-encapsulated Au@Ag-Au was obtained after ligand exchange operation. 2- Due to the chemical affinity, the surface ligand citrate of the nanoparticles was replaced and anchored on the Au@Ag-Au surface, and the Raman characteristic peak of SO2 (613cm -1 , 920cm -1 ) and the Raman characteristic peak position of the internal standard molecule 4-MBA (204 cm -1 ,1078cm -1 ,1587cm -1 ) are independent of each other and will not interfere with each other, and are not affected by BSA, HCl, L-lysine, I-, PO4 3- 、HPO4 2- , Cl - , glucose, CN - 、CO3 2- The interference of vitamin C and sulfite can only be measured when there is a significant SERS response, which can achieve the specific detection of SO2 residues.

[0048] In S1, the internal standard molecule 4-MBA is encapsulated in the gap between the Au core and the Ag-Au shell, which avoids the desorption of the internal standard molecule 4-MBA and prevents the reaction between 4-MBA and the analyte SO3 2- The competitive adsorption between them ensures reliable signal transduction during the substitution process and also isolates external environmental interference and possible aggregation;

[0049] In S1, HAuCl4 was used to prepare gold nanoparticles with a size of 15 nm by citric acid reduction method;

[0050] In S1, Au@Ag NPs are obtained by adding a gold nanoparticle solution, 100 mM CTAC, H2O and 100 mM NaOH into a beaker, stirring at 65°C, and then adding 1 mM AgNO3 solution and a mixed solution containing CTAC, AA and NaOH (20 mM CTAC, 2 mM AA and 2 mM NaOH) to react. After the reaction is complete, the mixture is cooled to room temperature and then centrifuged to obtain Au@Ag NPs.

[0051] In S1, the preparation of Au I The specific steps of the solution are as follows:

[0052] With 100mL of AuI Taking the solution preparation process as an example, 85.5 mL of H2O, 2 mL of 25 nM HAuCl4·3H2O, 2.5 mL of 100 mM NaOH, and 10 mL of 10 mM Na2SO3 were stirred until colorless and stored at 4°C.

[0053] In S1, Au@Ag-Au was synthesized by magnetically stirring H2O, 100 mM CTAC, Au@Ag NPs, and 10 -6 M of 4-MBA and 100 mM of AA were added and incubated to place the internal standard molecule 4-MBA in the gap between the nanoparticles. The purified 4-MBA-modified Au@Ag NPs were then obtained by centrifugation. Then 62.5 mL of Au I The solution was centrifuged to obtain Au@Ag-Au dispersed in H2O, which was then heated at 100°C for 30 min and cooled to room temperature to remove residual SO3 2- ;

[0054] In S1, the synthesized Au@Ag-Au has an Ag-Au shell thickness of 25 nm and a nanoparticle gap of 23.5 nm;

[0055] In S1, ligand exchange is performed by centrifuging 5 mL of Au@Ag-Au solution to obtain a lower precipitate, diluting it with 10 mL of a PSS solution containing 0.5 wt% PSS and 0.5 mM NaCl, shaking it, and then centrifuging it to obtain a lower precipitate, which is then resuspended with 10 mL of a PSS solution containing 0.5 wt% PSS and 0.5 mM NaCl, and then centrifuged and concentrated, and 5 mL of 5 mM TSC is added, and after shaking and centrifuging again, the citrate-coated Au@Ag-Au is collected;

[0056] In S1, the Au@Ag-Au@AAO substrate was prepared by dropping 200 μL of citrate-coated Au@Ag-Au on the entire surface of AAO and vacuum filtering for 1 min.

[0057] In S2, the Au@Ag-Au@AAO substrate is suspended in the center of the centrifuge tube, and the Au@Ag-Au@AAO substrate is used as a solid phase extraction material to adsorb and enrich SO2 in the sample to be tested;

[0058] In S2, the extracting solution is phosphoric acid, the volume percentage concentration of phosphoric acid is 5%, and 2 mL of phosphoric acid is added to every 1 g of the sample to be tested;

[0059] In S2, the centrifuge tube is sealed and heated in a water bath to extract SO2, the headspace extraction temperature is 25-100°C, and the extraction time is 5-30min;

[0060] If the headspace sampling conditions are: using 5% by volume concentration of phosphoric acid as the extraction solution, the headspace extraction temperature is 55°C and the extraction time is 15 minutes.

[0061] In S3, after the extraction is completed, the Au@Ag-Au@AAO substrate is taken out, and a handheld Raman spectrometer is used to perform SERS detection to obtain SERS spectrum data of the sample to be tested. By comparing with the SO2 detection limit, it can be determined whether the sample to be tested contains SO2, or by comparing with the standard curve, the SO2 content in the sample to be tested can be calculated;

[0062] In S3, the standard curve was drawn by preparing a series of Na2SO3 standard solutions, and performing SO2 headspace sampling and SERS detection in the same way. -1 The characteristic Raman peak height of SO2 at 1078 cm -1 A linear regression was performed between the ratio of the characteristic Raman peak heights of 4-MBA and the corresponding SO2 concentration value.

[0063] The main instruments used in the following examples are as follows:

[0064] Instruments: portable handheld Raman instrument (BWS499TS, B&W Tek Inc, USA), InVia Renishaw Raman microscope system (Renishaw, UK), scanning electron microscope (SEM; Zeiss, Ultra Plus), transmission electron microscope (TEM; FEI, Talos F200X), transmission electron microscope (TEM; JEOL, JEM-2100);

[0065] The main reagents used in the following examples are as follows:

[0066] Reagents: tetrachloroacid trihydrate (HAuCl4·3H2O), hexadecyltrimethylammonium chloride (CTAC), rhodamine 6G (R6G) and trisodium citrate (TSC) were purchased from Sigma (St. Louis, MO, USA); sodium hydroxide (NaOH), hydrochloric acid (HCl), I-lysine, disodium hydrogen phosphate (Na2HPO4), sodium dihydrogen phosphate (NaH2PO4), sodium chloride (NaCl), sodium carbonate (Na2CO3), phosphoric acid (H3PO4), hydrogen peroxide (H2O2) and silver nitrate (AgNO3); mercaptobenzoic acid (4-MBA), ascorbic acid (AA) and sodium sulfite (Na2SO3) were purchased from Aladdin Co., Ltd., Shanghai, China. Poly(sodium 4-styrenesulfonate) (PSSMw~70000), potassium iodide (KI), glucose and potassium ferrocyanide (K3[Fe(CN)6]) were obtained from Shanghai McLean Plant; AAO template (DP100-060-50000) was purchased from Shenzhen Topological Technology Co., Ltd., China; the Chinese medicines used in the recovery experiments were all from East China Chinese Medicine Co., Ltd. (Hangzhou, China); the Chinese medicines for the actual sample experiments were provided by Hangzhou Food and Drug Inspection Institute; all aqueous solutions were prepared with ultrapure water.

[0067] Example 1: Preparation of Au@Ag-Au@AAO substrate

[0068] Step 1: Preparation of gold nanoparticles

[0069] Gold nanoparticles with a size of 15 nm were prepared using HAuCl4 through citric acid reduction method;

[0070] Step 2: Preparation of Au@Ag NPs

[0071] 2 mL of gold nanoparticle solution, 4 mL of 100 mM CTAC, 33.96 mL of H2O and 0.04 mL of 100 mM NaOH were added to a beaker and stirred at 65 °C. 22 mL of 1 mM AgNO3 solution and 22 mL of a mixed solution containing CTAC, AA and NaOH (20 mM CTAC, 2 mM AA and 2 mM NaOH) were reacted by a syringe pump at an injection speed of 200 μL / min. After the reaction was complete, the mixture was cooled to room temperature and centrifuged at 6000 rpm for 10 min to obtain Au@Ag NPs.

[0072] Step 3: Preparation of Au@Ag-Au nanoparticles

[0073] First prepare Au I Solution: Mix 85.5 mL of H2O, 2 mL of 25 nM HAuCl4·3H2O, 2.5 mL of 100 mM NaOH, and 10 mL of 10 mM Na2SO3 by stirring until it becomes colorless and store at 4°C.

[0074] 38 mL of H2O, 5 mL of 100 mM CTAC, 5 mL of Au@Ag NPs, and 2 mL of 10 -6 M of 4-MBA and 0.5 mL of 100 mM AA were incubated for 2 h to place the internal standard molecule 4-MBA in the gaps between the nanoparticles. The nanoparticles were then centrifuged at 5000 rpm for 10 min to obtain purified 4-MBA-modified Au@Ag NPs. Then, 62.5 mL of Au@Ag was added dropwise at a rate of 2.5 mL / min. I The solution was centrifuged at 4000 rpm for 5 min to obtain Au@Ag-Au dispersed in 5 mL of H2O, which was then heated at 100 °C for 30 min and cooled to room temperature to remove residual SO3 2- ;

[0075] Step 4: Ligand exchange on substrate surface

[0076] Take 5 mL of Au@Ag-Au solution and centrifuge at 3500 rpm for 5 min to obtain the lower precipitate, which is then diluted with 10 mL of PSS solution containing 0.5 wt% PSS and 0.5 mM NaCl, shaken for 1 h, and then centrifuged at 3000 rpm for 4 min to obtain the lower precipitate, which is then resuspended with 10 mL of PSS solution containing 0.5 wt% PSS and 0.5 mM NaCl, then centrifuged and concentrated at 2500 rpm for 4 min, 5 mL of 5 mM TSC is added, shaken on a shaker for 12 h, and then centrifuged to collect the citrate-coated Au@Ag-Au;

[0077] Step 5: Preparation of Au@Ag-Au@AAO substrate

[0078] 200 μL of Au@Ag-Au coated with citrate was dropped on the entire surface of AAO and vacuum filtered for 1 min to obtain Au@Ag-Au@AAO substrate. Figure 2 (a) shown.

[0079] Example 2: SEM Characterization of AAO and Au@Ag-Au@AAO Substrates

[0080] AAO and the optimized Au@Ag-Au@AAO SERS substrates were characterized by scanning electron microscopy (SEM; Zeiss, Ultra Plus). Figure 3 As shown, the left side is the SEM image of AAO, and the right side is the SEM image of Au@Ag-Au@AAO substrate. The nanoparticles are closely arranged and evenly distributed on the AAO surface, with high sensitivity and uniformity.

[0081] Example 3: Investigating the specificity of Au@Ag-Au@AAO substrate performance

[0082] Au@Ag-Au@AAO substrate was exposed to BSA, HCl, L-lysine, I - PO4 3- 、HPO4 2- , Cl - , glucose, CN - 、CO3 2- SERS spectra after interference factors such as vitamin C (VC), such as Figure 4 As shown, only when sulfite is present can a significant SERS response be measured. 613cm -1 / I 1078cm -1 , while the presence of the other 11 substances did not trigger obvious signals. Even at a concentration 10 times higher than that of sulfite, all potential interferences had little effect on SO2 detection, proving that the strategy has good selectivity. Combined with headspace extraction, SO2 can be separated from the complex matrix of traditional Chinese medicine and reduce possible detection background interference.

[0083] Example 4: Investigating the uniformity of random points on the surface of Au@Ag-Au@AAO substrate

[0084] In order to evaluate the uniformity of the proposed SO2 sensor, a 100 × 100 μm 2 In terms of area, on the same SERS substrate, with a step length of 5 μm, 441 points of SERS images of 250 mg / kg SO2 were collected, as shown in Figure 5 As shown, SO2 is 613 cm -1 and 4-MBA in 1078 cm -1 The relative standard deviations (rsd) of the SERS signal intensities of 613cm -1 / I 1078cm -1 The relative standard deviation (rsd) is 6.6%, and the good uniformity of the SERS signal is attributed to the correction of the 4-MBA signal, which corrects the fluctuations in the measurement process.

[0085] Example 5: Investigating the stability of Au@Ag-Au@AAO substrate

[0086] like Figure 6 As shown, the Au@Ag-Au@AAO substrate was used to measure the 10 -7 SERS spectrum of MR6G, 612 cm-1 The peak intensity at 1078 cm decreased by 8.2%. -1 The peak intensity at decreased by only 2.5%, indicating that the Au@Ag-Au@AAO SERS substrate has long-term stability for practical applications.

[0087] Example 6: Headspace sampling combined with ratiometric SERS sensor to detect SO2 content

[0088] Na2SO3 was used to simulate sulfur fumigation of traditional Chinese medicine. The Au@Ag-Au@AAO SERS substrate was suspended in the center of a 15ml centrifuge tube to absorb SO2. 1mL Na2SO3 and 2ml 5% H3PO4 of different concentrations were added. The tube was then sealed immediately and kept at 55℃ for 15min. Finally, the SERS substrate was taken out and the SERS signal was collected by Raman spectrometer. The laser power was 3mW, the excitation wavelength was 785nm, and the scattered light was collected by a 20x objective lens (NA=0.4). The integration time was 10s, and the baseline was corrected by WIRE 4.2 software.

[0089] In the SERS spectrum, 613 cm -1 and 920cm -1 The significant peak intensity at 613 cm is consistent with the SO2 concentration. 0.05 mg / kg SO2 can also -1 The characteristic SERS peak was identified at , which is far below the maximum allowable amount of SO2 specified in the pharmacopoeia. 613cm -1 and I 613cm -1 / I 1078cm -1 The quantitative calibration chart changes with SO2 concentration (500mg / kg-0.05mg / kg) as shown below: Figure 7 As shown, the R 2 The values ​​are 0.9851 and 0.9966 respectively, so I 613cm -1 / I 1078cm -1 It can provide more accurate quantitative analysis results of SO2 concentration.

[0090] Example 7: Investigation of the linear detection range of SO2 using a handheld Raman spectrometer

[0091] In order to facilitate the detection of authentic traditional Chinese medicine, a portable handheld Raman spectrometer was used instead of the bulky confocal Raman spectrometer, and the excitation power was set to 30 mW, the excitation wavelength to 785 nm, and the integration time to 5 s. Origin 9.5 (OriginLab, Canada) was used to perform baseline correction on the SERS spectra;

[0092] like Figure 8 (a) shows the SERS spectra of different concentrations of SO2 measured, and the relative SERS intensity of SO2 to 4-MBA (I 613cm -1 / I 1078cm -1 ) and SO2 concentration, such as Figure 8 (b) shows that the linear detection range is 0.5mg / kg-500mg / kg, R 2 It is 0.9943.

[0093] Example 8: Detection of SO2 in Chinese herbal medicine

[0094] The residual SO2 content in 9 kinds of traditional Chinese medicines provided by Hangzhou Food and Drug Inspection was quantitatively analyzed, and the qualification of traditional Chinese medicines was judged by referring to the limit standard of the Chinese Pharmacopoeia. It is worth noting that for traditional Chinese medicine samples whose SO2 content exceeds the linear detection range of the method in this paper, the quantification of the residual SO2 is achieved by reducing the sampling amount. Table 1 shows the SO2 content in 9 kinds of traditional Chinese medicines determined by the proposed method and the standard analysis method (distillation titration method) specified in the Chinese Pharmacopoeia.

[0095]

[0096] Table 1 SO2 content in 9 traditional Chinese medicines

[0097] like Fig. 9 As shown in the figure, the distillation titration method and the ratio SERS sensor were used to perform linear fitting on the detection results of SO2 residues between traditional Chinese medicines, and the square correlation coefficient R 2 The error is 0.998 and the mean square error is 0.561. The results show that the difference between the two methods is small, which strongly proves the accuracy and reliability of the method in practical applications.

[0098] In summary, the present invention provides a method for rapid detection of SO2 by ratiometric SERS based on headspace sampling. The Au@Ag-Au@AAO substrate can specifically adsorb SO2 gas and display Raman characteristic peaks while enhancing the Raman signal intensity. An internal standard molecule 4-MBA is provided in the Au@Ag-Au gap, which can calibrate the random fluctuation of the SERS signal. The quantitative detection of SO2 is achieved by peak ratio analysis of the characteristic peak of SO2 gas and the characteristic peak of the internal standard molecule, and a good linear relationship is shown in the detection range of 0.5mg / kg-500mg / kg. The present invention can achieve high-sensitivity and rapid detection of SO2 residues in traditional Chinese medicine. The method has high-sensitivity detection capability and is simple to operate. It is suitable for on-site rapid detection of sulfite or SO2 in food safety and environmental supervision. In addition, by modifying different surface ligands on the surface of Au@Ag-Au nanoparticles, the method can be extended to the detection of more gases, such as aldehydes.

[0099] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for rapid detection of SO2 by ratiometric SERS based on headspace sampling, characterized in that: The following steps are involved: S1. Preparation of Au@Ag-Au@AAO substrate Gold nanoparticles were prepared by reducing HAuCl4 with trisodium citrate, and then the gold nanoparticle solution and a mixed solution containing CTAC, H2O, and NaOH were added to a beaker for heating and stirring, and then AgNO3 and a mixed solution containing CTAC, AA, and NaOH were added for reaction. After the reaction was complete, the mixture was cooled to room temperature and centrifuged to obtain Au@Ag NPs. At the same time, Au I Solution, H2O, CTAC, Au@Ag NPs, 4-MBA, AA were mixed by magnetic stirring, so that the internal standard molecule 4-MBA was placed in the gap between the nanoparticles, and then centrifuged to obtain purified 4-MBA-modified Au@Ag NPs, and then Au I solution, synthesizing Au@Ag-Au, and then performing ligand exchange to obtain citrate-coated Au@Ag-Au, which was then dropped on AAO and the Au@Ag-Au@AAO substrate was prepared by vacuum filtration; S2, adsorption of SO2 The sample to be tested and the extract were added into a centrifuge tube, and the SO2 gas was obtained by the headspace sampling method. The Au@Ag-Au@AAO substrate was used as a solid phase extraction material to adsorb SO2; S3. Calculate the residual SO2 The Au@Ag-Au@AAO substrate was tested using SERS technology to obtain the SERS spectrum data of the sample to be tested, and the residual SO2 in the sample to be tested was calculated based on the standard curve.

2. The method for rapid detection of SO2 by ratiometric SERS based on headspace sampling according to claim 1, characterized in that: In S1, the size of the gold nanoparticles is 15 nm.

3. The method for rapid detection of SO2 by ratiometric SERS based on headspace sampling according to claim 1, characterized in that: In S1, the preparation of Au I The specific steps of the solution are as follows: With 100mL of Au I Taking the solution preparation process as an example, 85.5 mL of H2O, 2 mL of 25 nM HAuCl4·3H2O, 2.5 mL of 100 mM NaOH, and 10 mL of 10 mM Na2SO3 were stirred and mixed until colorless.

4. The method for rapid detection of SO2 by ratiometric SERS based on headspace sampling according to claim 1, characterized in that: In S1, the Au I Solution, the solution volume is 62.5mL.

5. The method for rapid detection of SO2 by ratiometric SERS based on headspace sampling according to claim 1, characterized in that: In S1, Au@Ag-Au was synthesized, the Ag-Au shell thickness was 25 nm, and the nanoparticle gap was 23.5 nm.

6. The method for rapid detection of SO2 by ratiometric SERS based on headspace sampling according to claim 1, characterized in that: In S1, the ligand is exchanged, the Au@Ag-Au solution is centrifuged to obtain a lower precipitate, which is diluted with a PSS solution, shaken and then centrifuged to obtain a lower precipitate, which is resuspended with a PSS solution, then centrifuged and concentrated, TSC is added, and after sufficient shaking, the Au@Ag-Au coated with citrate is collected by centrifugation.

7. The method for rapid detection of SO2 by ratiometric SERS based on headspace sampling according to claim 6, characterized in that: The volume of TSC was 5 mL and the concentration was 5 mM.

8. The method for rapid detection of SO2 by ratiometric SERS based on headspace sampling according to claim 1, characterized in that: In S1, the Au@Ag-Au coated with the citrate layer is dropped onto the entire surface of AAO, and the vacuum filtration time is 1 min.

9. The method for rapid detection of SO2 by ratiometric SERS based on headspace sampling according to claim 1, characterized in that: In S2, the extracting solution is phosphoric acid, the volume percentage concentration of the phosphoric acid is 5%, 2 mL of phosphoric acid is added to every 1 g of the sample to be tested, the extraction temperature of the headspace sampling method is 25-100° C., and the extraction time is 5-30 min.

10. The method for rapid detection of SO2 by ratiometric SERS based on headspace sampling according to claim 1, characterized in that: In S3, the method for drawing the standard curve is as follows: Prepare Na2SO3 standard solution, and perform SO2 headspace sampling and SERS detection in the same way. -1 The characteristic Raman peak height of SO2 at 1078 cm -1 A linear regression was performed between the ratio of the characteristic Raman peak heights of 4-MBA and the corresponding SO2 concentration value.

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