A method for rapidly detecting BaP in edible oil based on LLE-SERS modified silver nanomaterial

Abstract

The application belongs to the technical field of food safety detection, and specifically discloses a method for detecting BaP in edible oil by using CTAB modified silver nanomaterial based on LLE-SERS, which comprises the following steps: preparing Ag nanoparticle sol, preparing CTAB functionalized Ag nanoparticle sol, SERS detection of BaP standard aqueous solution with different concentrations, fitting a standard curve, extracting BaP and performing SERS detection. The synthetic raw materials of the surface CTAB functionalized Ag nanoparticles used in the application are simple, and the coverage degree of the ligand molecules CTAB on the surface of the Ag nanoparticles can be controlled and adjusted. The CTAB as the surface ligand can directly capture and enrich BaP molecules. The detection method is high in stability, and can effectively avoid the problem that different batches of samples produce different effects in the Raman test.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of food safety detection, and particularly relates to a method for detecting BaP in edible oil based on LLE-SERS of CTAB modified silver nanomaterials. BACKGROUND

[0002] Edible oil is a necessity for human life and is very easy to be contaminated by benzo[a]pyrene (BaP), which involves many processes such as planting, airing, processing and transporting of oil crops. It is well known that BaP is one of the carcinogens with strong toxicity, and has strong lipophilicity, which is easy to be stored in edible oil for a long time and seriously harms human health. Long-term consumption of edible oil containing BaP will cause serious and irreversible harm to the human body, so it is very important to realize trace detection of BaP in edible oil for protecting life and health. The detection of BaP in edible oil mainly includes two basic processes of sample pretreatment and determination. At present, a large number of traditional technologies are used for the detection of BaP, such as gas chromatography-mass spectrometry, high performance liquid chromatography-mass spectrometry, supercritical fluid chromatography, fluorescence spectrophotometry, high performance liquid chromatography-fluorescence detection method, etc. These methods have been used for food safety and quality control. Although these detection technologies have high sensitivity and strong resolution ability, they can realize accurate detection of BaP, but the detection instruments have high requirements for samples, and most of them need to be pretreated for a long time before detection. At the same time, these large instruments are often expensive, which cannot meet the needs of on-site detection, portable and rapid, and their wide application is limited. Therefore, it is very important to develop a rapid, high-sensitivity and low-cost technology for on-site detection of BaP.

[0003] Surface-enhanced Raman spectroscopy (SERS), a promising spectroscopic technique, is a type of "fingerprint" vibrational spectroscopy developed based on Raman spectroscopy. Through electromagnetic and chemical enhancement, it achieves highly sensitive and non-destructive analysis of molecules. Furthermore, due to its independence from water solvents and ease of operation, it is widely used in food safety, including the detection of antibiotics, biotoxins, food additives, pathogens, and other harmful substances. Currently, strategies for trace BaP detection in edible oils using SERS technology mainly fall into two categories: one focuses on SERS substrates with sufficiently high enhancement effects and strong affinity for BaP, as exemplified by the research conducted by the aforementioned scholars, aiming to improve the sensitivity and selectivity of SERS enhancement for BaP; the other focuses on developing efficient pretreatment methods to achieve effective extraction, separation, enrichment, and concentration of BaP in edible oils. This is the key technology for achieving trace BaP detection in edible oils. Since edible oils contain a large amount of fat, resulting in a complex lipid matrix, and BaP has high lipophilicity, the pretreatment process is crucial. Currently, pretreatment methods for BaP detection in edible oils can be divided into two processes: separation and purification. Separation methods mainly include saponification, Soxhlet extraction, liquid-liquid extraction, and microwave-assisted extraction; purification methods mainly include column chromatography, solid-phase extraction, and magnetic solid-phase extraction. These processes are time-consuming, complex, consume large amounts of solvent, and are costly. Pretreatment of edible oils remains a significant challenge; therefore, finding suitable pretreatment methods and developing rapid detection methods based on SERS is of great importance. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method for detecting BaP in edible oils using CTAB-modified silver nanomaterials based on LLE-SERS, which combines CTAB-functionalized Ag nanoparticles to achieve rapid trace detection of BaP.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: a method for detecting BaP in edible oil using CTAB-modified silver nanomaterials based on LLE-SERS, comprising the following steps:

[0006] (1) Preparation of Ag nanoparticle sol;

[0007] (2) Preparation of CTAB-functionalized Ag nanoparticle sol: Add CTAB to the Ag nanoparticle sol prepared in step (1)

[0008] By incorporating ligands and adjusting the amount of CTAB added, Ag nanoparticle sol Ag@CTAB with the best enhancement effect was obtained;

[0009] (3) SERS detection of BaP standard aqueous solutions of different concentrations: Ag nanoparticles prepared in step (2) were used.

[0010] SERS was performed on aqueous solutions of BaP standard at different concentrations using sol-Ag@CTAB, and SERS spectra were obtained.

[0011] (4) Fitting the standard curve: The spectral intensity in the SERS spectrum obtained in step (3) and the BaP standard water are compared.

[0012] Plot the logarithm of the solution concentration and fit it to obtain a standard curve;

[0013] (5) Extracting BaP and performing SERS detection: Dimethyl sulfoxide (DMSO) was added to the edible oil sample to be tested.

[0014] Take out the BaP, then use toluene to back-extract the BaP from the DMSO, and finally dry and re-dissolve it before Raman detection. If the characteristic peak of BaP appears in the SERS spectrum, it indicates that the sample contains BaP, and the concentration of BaP in the sample is quantitatively determined according to the standard curve obtained in step (4).

[0015] In a preferred embodiment of the present invention, the Ag nanoparticle sol in step (1) is synthesized by adjusting the amount of silver nitrate and CA added based on the traditional sodium citrate reduction method, and the particle size of the Ag nanoparticle sol is 70-90 nm.

[0016] In a preferred embodiment of the present invention, the volume ratio of ligand molecule CTAB to Ag nanoparticle sol in step (2) is (5-15):(150-250).

[0017] In a preferred embodiment of the present invention, step (2) involves adjusting the concentration of added ligand molecules to obtain Ag nanoparticle sol Ag@CTAB with adjustable surface functionalization and controlling the coverage of CTAB on the surface of Ag nanoparticles.

[0018] In a preferred embodiment of the present invention, in step (2), the ligand molecule CTAB can directly capture and enrich the BaP molecule to be tested.

[0019] In a preferred embodiment of the present invention, the laser wavelength used for SERS detection in steps (3) and (5) is 785 nm, the power is 100 mW, and the exposure time is 2 s.

[0020] In a preferred embodiment of the present invention, the amount of DMSO added to the edible oil sample to be tested in step (5) is 3-5 mL / g.

[0021] In a preferred embodiment of the present invention, the volume ratio of toluene to DMSO in step (5) is 1:1.

[0022] In a preferred embodiment of the present invention, the solvent used for resolution in step (5) is deionized water.

[0023] The principle of this invention is as follows: The surface of Ag nanoparticles exhibiting surface plasmon resonance (SPR) is modified with the ligand molecule CTAB. The coverage of CTAB on the Ag nanoparticle surface can be controlled by changing the ligand concentration. Positively charged ammonium molecules in CTAB are tightly adsorbed onto the Ag nanoparticle surface through strong electrostatic interactions, while the hydrophobic alkyl chains point outwards towards the solution phase. This hydrophobic interaction adsorbs and concentrates hydrophobic BaP molecules from the environment, fixing them in the electromagnetic field enhancement region. After aggregation, the molecular Raman signal is amplified, thus enabling the detection of BaP. When CTAB reaches an appropriate coverage level, the molecular signal of BaP can be amplified to the maximum extent. Simultaneously, this study provides a simple, rapid, and sensitive pretreatment method for detecting trace BaP molecules in edible oils. Specifically, a two-step liquid-liquid extraction-surface-enhanced Raman spectroscopy (LLE-SERS) strategy is developed. First, BaP in edible oils is extracted using dimethyl sulfoxide (DMSO), then BaP in DMSOs is back-extracted using toluene, and finally, after drying and reconstitution, the samples are detected. The entire process avoids interference from the base oil, confirming the value of this strategy in the trace detection of benzo[a]pyrene (BaP) in edible oils.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The raw materials for synthesizing the surface-CTAB-functionalized Ag nanoparticles used in this invention are simple, and the coverage of the CTAB ligand molecule on the surface of the Ag nanoparticles can be controlled and adjusted; CTAB, as a surface ligand, can directly capture and enrich BaP molecules.

[0026] 2. The detection method of the present invention has high stability and effectively avoids the problem of different batches of samples producing different results in Raman testing;

[0027] 3. In this invention, CTAB is used as a surface ligand to effectively capture and enrich BaP molecules. At the same time, a two-step liquid-liquid extraction-surface-enhanced Raman spectroscopy coupling strategy is developed to effectively extract BaP from edible oil and enhance the signal intensity of BaP molecules. The surface-functionalized Ag nanoparticles combined with the two-step liquid-liquid extraction method and Raman technology can effectively identify BaP.

[0028] 4. The LLE-SERS-based CTAB-functionalized Ag nanoparticles in this invention can be used to detect BaP in edible oils rapidly, demonstrating the great potential of this method in practical applications. Attached Figure Description

[0029] Figure 1Scanning electron microscope (SEM) image of Ag nanoparticles;

[0030] Figure 2 For multiple parallel samples, 1380cm -1 Verification of the stability of characteristic peak Raman intensity over time from 0 to 180 s;

[0031] Figure 3 The pure mass spectrum, SERS spectrum, and blank control spectrum of benzo[a]pyrene;

[0032] Figure 4 The fitted curve of the target peak intensity ratio as a function of BaP concentration;

[0033] Figure 5 Screening diagram of extractants for back-extraction of BaP from DMSO. Detailed Implementation

[0034] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in more detail below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to these embodiments.

[0035] Example 1

[0036] A method for detecting BaP in edible oils using CTAB-modified silver nanomaterials based on LLE-SERS includes the following steps:

[0037] (1) Preparation of Ag nanoparticle sol: Heat 200 mL of 1 mM AgNO3 aqueous solution to boiling.

[0038] Add 5 mL of 1 wt% sodium citrate aqueous solution to the solution. The solution color gradually changes from transparent to gray-green. Continue boiling for 3 hours, then stop the reaction and let it cool naturally to finally obtain Ag nanoparticle sol with a particle size of 80 nm. Figure 1 The image shows a scanning electron microscope (SEM) image of Ag nanoparticle sol. As can be seen from the image, the Ag nanoparticle sol has a uniform particle size.

[0039] (2) Preparation of CTAB-functionalized Ag nanoparticle sol: Ag nanoparticles with uniform morphology prepared in step (1)

[0040] The ligand hexadecyltrimethylammonium bromide (CTAB) was added to the Ag nanoparticle sol at a volume ratio of CTAB to Ag nanoparticle sol of 10:200. The temporal stability of the Raman signal of BaP detected by the CTAB-functionalized Ag nanoparticle sol (Ag@CTAB) obtained in the above synthesis was verified. The laser wavelength was 785 nm, the power was 100 mW, and the exposure time was 2 s. The results are as follows: Figure 2In multiple parallel samples, 1380 cm -1 The characteristic peak Raman intensity of the SERS signal within the range of 0-180 s showed a relative standard deviation of only 3.01%. This indicates that the signal exhibits good stability within 180 s after sample preparation, which is crucial for the detection of actual samples.

[0041] (3) Detection of BaP standard aqueous solutions of different concentrations: Observe the BaP detection sensitivity of this strategy by testing different concentrations of BaP standard aqueous solutions.

[0042] Aqueous solutions of BaP standard (500, 100, 50, 10, 5, 1, 0.5 μg / L) were added to Ag@CTAB nanoparticle sol, and Raman spectroscopy was performed under a 785 nm laser with a power of 100 mW and an exposure time of 2 s. The results are as follows. Figure 3 As shown. Figure 3 The images, from bottom to top, show the pure mass spectrum, SERS spectrum, and blank control spectrum of benzo[a]pyrene. As can be seen from the figures, the SERS peaks of benzo[a]pyrene (BaP) are essentially consistent with its solid Raman peaks. After comparison, the peaks at 612, 636, 1385, and 1580 cm⁻¹ can be confirmed. -1 The characteristic peaks of benzo[a]pyrene (BaP) are at 612 cm⁻¹. -1 Bending vibrations attributed to C-C, CH bonds, also at 636 cm⁻¹. -1 It also belongs to the bending vibration of the C-C,CH bond, and at 1385 cm⁻¹ it belongs to the stretching vibration of the C-C bond, and at 1580 cm⁻¹ it belongs to the stretching vibration of the C-C bond. -1 It belongs to the stretching vibration of the C-C bond and the bending vibration of the CH bond.

[0043] (4) Fitting the standard curve: Plot the logarithms of the spectral intensities and the concentrations of the BaP standard aqueous solution in the above SERS spectra, and fit the curve to obtain the standard curve; Figure 4 As can be seen, 1380cm -1 The spectral intensity at a given concentration changes with the concentration of BaP. When the concentration of benzo[a]pyrene (BaP) reaches 50 μg / L, the signal of the benzo[a]pyrene (BaP) standard tends to stabilize and no longer shows linear growth. This is because the local surface plasmons (LSPs) provided by silver nanoparticles are limited. After enough benzo[a]pyrene (BaP) molecules are adsorbed, the silver sol cannot provide more LSPs for more molecules, causing the relationship between the SERS intensity and concentration at high concentrations to no longer be linear. When the concentration is taken as log10, there is a good linear relationship between the two, i.e., R 2 =0.989, the lowest distinguishable concentration of BaP is 0.5 ppb.

[0044] (5) Extraction of BaP from a simulated edible oil system and SERS detection: Extractants for BaP back-extraction from DMSO were screened. Different extractants (toluene, n-hexane, cyclohexane, petroleum ether, isooctane) were added to the DMSO extractant used in the first extraction step for a second extraction. After nitrogen blowing, water was added for redissolution. Raman spectroscopy was performed under a 785nm laser with a power of 100mW and an exposure time of 2s. The results are as follows: Figure 5 As shown, from Figure 5 As can be seen, due to the π-π interaction between BaP molecules and toluene molecules, the extraction effect of BaP is significantly better than that of the other four organic reagents, achieving highly efficient extraction of BaP; different concentrations of BaP standard solutions were added to edible oil and mixed evenly to prepare BaP solutions of different concentrations (500 ppb).

[0045] Edible oil samples with concentrations of 200 ppb, 100 ppb, 50 ppb, and 10 ppb were extracted from the edible oil samples containing different concentrations of BaP by adding dimethyl sulfoxide (DMSO). Then, toluene was used to back-extract the BaP from the DMSO. Finally, after drying and reconstitution, SERS analysis was performed.

[0046] The above embodiments verify that the LLE-SERS-based detection method is feasible for detecting BaP-containing simulated edible oil systems.

[0047] CTAB ligand molecules were modified onto the surface of Ag nanoparticles exhibiting surface plasmon resonance (SPR) to obtain surface-functionalized Ag nanoparticle sols. Subsequently, BaP solutions of different concentrations were analyzed, and Raman spectroscopy using SERS technology confirmed the high sensitivity of this invention in the analysis and detection of BaP. Finally, extraction tests were performed on edible oils containing different concentrations of BaP, demonstrating the sensitivity of this method in practical applications. This invention is simple to operate, fast in detection, and highly practical, and can be applied to the trace detection of BaP in edible oils.

[0048] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for detecting BaP in edible oil based on LLE-SERS modified silver nanomaterials, characterized in that, The method comprises the following steps: (1) preparing Ag nanoparticle sol; (2) preparing CTAB functionalized Ag nanoparticle sol: adding a ligand to the Ag nanoparticle sol prepared in step (1), and obtaining the Ag nanoparticle sol Ag@CTAB with the best enhancement effect by adjusting the amount of CTAB added; (3) SERS detection of BaP standard aqueous solutions with different concentrations: using the Ag nanoparticle sol Ag@CTAB prepared in step (2) to perform SERS detection on BaP standard aqueous solutions with different concentrations, and obtaining SERS spectra; (4) fitting a standard curve: plotting the spectral intensity in the SERS spectra obtained in step (3) against the logarithm of the concentration of the BaP standard aqueous solution, and fitting to obtain a standard curve; (5) extracting BaP and performing SERS detection: adding dimethyl sulfoxide to the edible oil sample to be detected to extract BaP therefrom, using toluene to extract BaP from DMSO, and then performing Raman detection after drying and redissolving; if the characteristic peaks of BaP appear in the SERS spectra, it indicates that the sample to be detected contains BaP, and the concentration of BaP in the sample can be quantitatively measured according to the standard curve obtained in step (4).

2. The method for detecting BaP in edible oil based on LLE-SERS modified silver nanomaterials according to claim 1, characterized in that, In step (1), the Ag nanoparticle sol is synthesized by adjusting the sodium citrate reduction method, so that the particle size of the Ag nanoparticle sol is 70-90 nm.

3. The method for detecting BaP in edible oil based on LLE-SERS modified silver nanomaterials according to claim 1, characterized in that, In step (2), the volume ratio of the ligand molecule CTAB to the Ag nanoparticle sol is (5-15):(150-250).

4. The method for detecting BaP in edible oil based on LLE-SERS modified silver nanomaterials according to claim 1, characterized in that, In step (2), the concentration of the ligand molecule is adjusted to obtain the Ag nanoparticle sol Ag@CTAB with adjustable surface functionalization degree and the coverage degree of CTAB on the surface of the Ag nanoparticle.

5. The method for detecting BaP in edible oil based on LLE-SERS-CTAB modified silver nanomaterials according to claim 1, characterized in that, In step (2), the ligand molecule CTAB can directly capture and enrich the BaP molecules to be detected.

6. The method for detecting BaP in edible oil based on LLE-SERS-CTAB modified silver nanomaterials according to claim 1, characterized in that, In steps (3) and (5), the laser wavelength used for SERS detection is 785 nm, the power is 100 mW, and the exposure time is 2 s.

7. The method for detecting BaP in edible oil based on LLE-SERS-CTAB modified silver nanomaterials according to claim 1, characterized in that, In step (5), the amount of DMSO added to the edible oil sample to be detected is 3-5 mL / g.

8. The method for detecting BaP in edible oil based on LLE-SERS-CTAB modified silver nanomaterials according to claim 1, characterized in that, In step (5), the volume ratio of toluene to DMSO is 1:

1.

9. The method for detecting BaP in edible oil based on LLE-SERS-CTAB modified silver nanomaterials according to claim 1, characterized in that, In step (5), the solvent used for redissolution is deionized water.

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