Method for rapidly detecting BaP in edible oil through CTAB modified silver nanomaterial based on LLE-SERS

Abstract

The invention belongs to the technical field of food safety detection, and particularly discloses a method for detecting BaP in edible oil by using a CTAB modified silver nanomaterial based on LLE-SERS, and the method comprises the following steps: preparing Ag nanoparticle sol, preparing CTAB functionalized Ag nanoparticle sol, performing SERS detection on BaP standard substance aqueous solutions with different concentrations, fitting a standard curve, extracting BaP and performing SERS detection. The synthesis raw materials of the Ag nanoparticles with the CTAB functionalized surfaces are simple, and the coverage degree of ligand molecules CTAB on the surfaces of the Ag nanoparticles can be controlled and adjusted; cTAB (Cetyltrimethyl Ammonium Bromide) is used as a surface ligand to directly capture and enrich BaP molecules; the detection method disclosed by the invention is high in stability, and the problem that different batches of samples generate different effects in a Raman test is effectively avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of food safety detection, and in particular relates to a method for detecting BaP in edible oil by using CTAB-modified silver nanomaterials based on LLE-SERS. Background Art

[0002] Edible oil is a necessity for human life and is very susceptible to contamination by benzo[a]pyrene (BaP). This contamination involves multiple processes such as oil crop planting, drying, processing, and transportation of finished edible oil products. As we all know, BaP is one of the most toxic carcinogens. It has a strong lipophilicity and is easy to be stored in edible oil for a long time, which seriously endangers 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 achieve trace detection of BaP in edible oil to protect life and health. The detection of BaP in edible oil mainly includes two basic processes: 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, etc. These methods have been used for food safety and quality control. Although these detection technologies are highly sensitive and have strong resolution, and can accurately detect BaP, the detection instruments have high requirements for samples. Most of them require long and complex pre-treatment of samples before detection. At the same time, these large instruments are often expensive and cannot meet the requirements of portable and fast on-site detection, which limits their widespread application. Therefore, it is crucial to develop a fast, highly sensitive and low-cost technology for on-site detection of BaP.

[0003] Surface enhanced Raman spectroscopy (SERS) is a promising spectral technology. It is a type of "fingerprint" vibrational spectroscopy technology developed on the basis of Raman spectroscopy. It can achieve high-sensitivity and non-destructive analysis of molecules through electromagnetic field enhancement and chemical enhancement. At the same time, because it is not affected by solvent water and is simple to operate, it is widely used in the field of food safety, including the detection of other harmful substances such as antibiotics, biotoxins, food additives and pathogens. At present, the strategies for using SERS technology to detect trace amounts of BaP in edible oil are mainly divided into two categories. One is that the SERS substrate has a sufficiently high enhancement effect and has a strong affinity with BaP. For example, the research conducted by the above scholars is committed to improving the sensitivity of SERS enhancement and the selectivity of BaP. The other is to develop efficient pretreatment methods to achieve effective extraction, separation, enrichment and concentration of BaP in edible oil. This is the technical key to realizing the detection of trace amounts of BaP in edible oil. Since edible oil contains a large amount of fat, the lipid matrix is ​​complex, and BaP has high lipophilicity, the pretreatment process is very critical. At present, the pretreatment methods for BaP detection in edible oil can be divided into two processes: separation and purification. The main separation methods include saponification, Soxhlet extraction, liquid-liquid extraction, microwave-assisted extraction, etc.; the main purification methods include column chromatography, solid phase extraction, magnetic solid phase extraction, etc. These processes are time-consuming, complex to operate, consume a lot of solvents, and have high detection costs. At present, the pretreatment of edible oil is still a big challenge, so it is of great significance to find a suitable pretreatment method and develop a rapid detection method based on SERS. Summary of the invention

[0004] The purpose of the present invention is to overcome the defects of the prior art and provide a method for detecting BaP in edible oil by using CTAB-modified silver nanomaterials based on LLE-SERS, and to perform trace rapid detection of BaP by combining CTAB-functionalized Ag nanoparticles.

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

[0006] (1) preparing Ag nanoparticle sol;

[0007] (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 added CTAB;

[0008] (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 to obtain SERS spectra;

[0009] (4) fitting a standard curve: plotting the spectral intensity in the SERS spectrum obtained in step (3) against the logarithm of the concentration of the BaP standard aqueous solution, and fitting the result to obtain a standard curve;

[0010] (5) Extracting BaP and performing SERS detection: Dimethyl sulfoxide (DMSO) is added to the edible oil sample to extract the BaP therein, and then the BaP in the DMSO is stripped out using toluene. Finally, the sample is dried and redissolved before Raman detection. If a characteristic peak of BaP appears in the SERS spectrum, it indicates that the sample being tested contains BaP, and the concentration of BaP in the sample is quantitatively measured based on the standard curve obtained in step (4).

[0011] 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 70-90nm.

[0012] In a preferred embodiment of the present invention, the volume ratio of the ligand molecule CTAB to the Ag nanoparticle sol in step (2) is (5-15):(150-250).

[0013] In a preferred embodiment of the present invention, in step (2), the concentration of the added ligand molecules is adjusted to obtain the Ag nanoparticle sol Ag@CTAB with adjustable surface functionalization degree and to regulate the coverage degree of CTAB on the surface of the Ag nanoparticles.

[0014] In a preferred embodiment of the present invention, in step (2), the ligand molecule CTAB can directly capture and enrich the BaP molecules to be detected.

[0015] 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.

[0016] 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.

[0017] In a preferred embodiment of the present invention, the volume ratio of toluene to DMSO in step (5) is 1:1.

[0018] In a preferred embodiment of the present invention, the solvent used for re-dissolution in step (5) is deionized water.

[0019] The principle of the present invention is as follows: the surface of Ag nanoparticles with surface plasmon resonance effect is modified with ligand molecule CTAB, and the coverage of CTAB on the surface of Ag nanoparticles can be regulated by changing the ligand concentration. The positively charged ammonium molecules in CTAB can be tightly adsorbed on the surface of AgNPs through strong electrostatic action, while the hydrophobic alkyl chains point outward to the solution phase, adsorb and concentrate the hydrophobic molecules BaP in the environment through hydrophobic action, and fix them in the electromagnetic field enhancement area. After agglomeration, the molecular Raman signal is amplified, thereby realizing the detection of BaP. When CTAB reaches an appropriate coverage, the molecular signal of BaP can be amplified to the greatest extent. At the same time, this study provides a simple, rapid and sensitive pretreatment method for detecting trace BaP molecules in edible oil, that is, a two-step liquid-liquid extraction-surface enhanced Raman spectroscopy coupling (LLE-SERS) strategy is developed, firstly, BaP in edible oil is extracted using dimethyl sulfoxide, then BaP in dimethyl sulfoxide is stripped out using toluene, and finally detection is performed after drying and redissolving. The whole process avoided interference from matrix oil, confirming the value of this strategy in the detection of trace amounts of benzo[a]pyrene (BaP) in edible oils.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The raw materials for the synthesis of the Ag nanoparticles functionalized with surface CTAB used in the present invention are simple, and the coverage of the ligand molecule CTAB on the surface of the Ag nanoparticles can be controlled and adjusted; CTAB as a surface ligand can directly capture and enrich BaP molecules;

[0022] 2. The detection method of the present invention has high stability, which effectively avoids the problem that different batches of samples produce different effects in Raman testing;

[0023] 3. In the present invention, CTAB is used as a surface ligand to effectively capture and enrich BaP molecules, and 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;

[0024] 4. The CTAB-functionalized Ag nanoparticles based on LLE-SERS in the present invention can be used for rapid detection of BaP in edible oil, which proves that this method has great potential in practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1is a scanning electron microscope (SEM) image of Ag nanoparticles;

[0026] Figure 2 For multiple parallel samples, 1380cm -1 Verification of the time stability of the characteristic peak Raman intensity from 0 to 180 seconds;

[0027] Figure 3 The pure mass spectrum, SERS spectrum and blank control spectrum of benzo[a]pyrene;

[0028] Figure 4 is the fitting curve of the target peak intensity ratio changing with BaP concentration;

[0029] Figure 5 The figure shows the screening of extractants for stripping BaP from DMSO. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is described in more detail below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to these embodiments.

[0031] Example 1

[0032] A method for detecting BaP in edible oil using CTAB-modified silver nanomaterials based on LLE-SERS, comprising the following steps:

[0033] (1) Preparation of Ag nanoparticle sol: 200 mL of 1 mM AgNO3 aqueous solution was heated to boiling, and 5 mL of 1 wt% sodium citrate aqueous solution was added. The color of the solution gradually changed from transparent to gray-green. The solution was boiled for 3 h, and then the reaction was stopped and cooled naturally to obtain Ag nanoparticle sol with a particle size of 80 nm. Figure 1 This is a scanning electron microscope (SEM) image of the Ag nanoparticle sol. It can be seen from the figure that the particle size of the Ag nanoparticle sol is uniform;

[0034] (2) Preparation of CTAB-functionalized Ag nanoparticle sol: Adding ligand molecule hexadecyltrimethylammonium bromide (CTAB) to the uniform morphology Ag nanoparticle sol prepared in step (1), the volume ratio of ligand molecule CTAB to Ag nanoparticle sol being 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, the exposure time was 2 s, and the results were as follows: Figure 2 In multiple parallel samples, 1380cm -1The relative standard deviation of the characteristic peak Raman intensity in the SERS intensity of 0-180s is only 3.01%, which shows that the signal shows good stability within 180s after sample preparation, which is very important for the detection of actual samples.

[0035] (3) Detection of BaP standard aqueous solutions with different concentrations: To observe the BaP detection sensitivity of this strategy, BaP standard aqueous solutions with different concentrations (500, 100, 50, 10, 5, 1, and 0.5 μg / L) were added to the Ag@CTAB nanoparticle sol and Raman tests were performed under a 785 nm laser, a power of 100 mW, and an exposure time of 2 s. The results are shown in Figure 2. Figure 3 shown. Figure 3 From bottom to top, the pure mass spectrum, SERS spectrum and blank control spectrum of benzo[a]pyrene are shown. It can be seen from the figure that the SERS peak of benzo[a]pyrene (BaP) is basically consistent with its solid Raman peak. After comparison, it can be confirmed that 612, 636, 1385, 1580cm -1 is the characteristic peak of benzo[a]pyrene (BaP), among which 612cm -1 The bending vibrations of CC and CH bonds are similarly 636 cm -1 It is also attributed to the bending vibration of CC and CH bonds, 1385 cm-1 is attributed to the stretching vibration of CCC bonds, and 1580 cm-1 is attributed to the stretching vibration of CCC bonds. -1 It is attributed to the stretching vibration of CC bond and the bending vibration of CH bond.

[0036] (4) Fitting a standard curve: Plot the spectral intensity in the above SERS spectrum against the logarithm of the concentration of the BaP standard aqueous solution, and fit the result to obtain a standard curve; Figure 4 As you can see, 1380cm -1 The spectral intensity at changes with the change of BaP concentration. When the concentration of benzo[a]pyrene (BaP) reaches 50μg / L, the signal of benzo[a]pyrene (BaP) standard tends to be stable and no longer shows a linear growth. This is because the local surface plasmons (LSPs) provided by silver nanoparticles are limited. When enough benzo[a]pyrene (BaP) molecules are adsorbed, the silver sol cannot provide more LSPs for more molecules, resulting in the high concentration SERS intensity and concentration The relationship is no longer linear; when the concentration is taken as log10, there is a good linear relationship between the two, that is, R 2 =0.989, the lowest distinguishable concentration of BaP is 0.5ppb.

[0037] (5) Extraction of BaP from a simulated edible oil system and SERS detection: Screening of extractants for stripping BaP from DMSO. Adding different extractants (toluene, n-hexane, cyclohexane, petroleum ether, isooctane) to the extractant DMSO used to complete the first step of extraction for the second step of extraction. After nitrogen blowing, water was added to re-dissolve. Raman testing was performed under a 785 nm laser, a power of 100 mW, and an exposure time of 2 s. The results are shown in FIG. Figure 5 As shown, from Figure 5 It can be seen that due to the π-π force formed by BaP molecules and toluene molecules, the extraction effect of BaP is significantly better than that of the other four organic reagents, achieving efficient extraction of BaP; BaP standard solutions of different concentrations are added to edible oil and mixed evenly to prepare edible oil samples containing different concentrations of BaP (500ppb, 200ppb, 100ppb, 50ppb, 10ppb), and dimethyl sulfoxide (DMSO) is added to extract BaP from edible oil samples containing different concentrations of BaP, and then toluene is used to strip BaP from DMSO, and finally SERS detection is carried out after drying and redissolution.

[0038] The above examples verify that the application of the LLE-SERS-based detection method in the detection of simulated edible oil systems containing BaP is feasible.

[0039] The surface of Ag nanoparticles with surface plasmon resonance (SPR) was modified with ligand CTAB to obtain surface functionalized Ag nanoparticle sol; then, different concentrations of BaP solution were detected, and Raman test was performed using SERS technology, which confirmed that the present invention has high sensitivity in the analysis and detection of BaP; finally, edible oil containing different concentrations of BaP was extracted and tested, which showed the sensitivity of the method in practical application. The present invention is simple to operate, fast in detection speed, and highly practical, and can be applied to trace detection of BaP in edible oil.

[0040] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some or all of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for detecting BaP in edible oil using CTAB-modified silver nanomaterials based on LLE-SERS, characterized in that: The following steps are involved: (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 added CTAB; (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 to obtain SERS spectra; (4) fitting a standard curve: plotting the spectral intensity in the SERS spectrum obtained in step (3) against the logarithm of the concentration of the BaP standard aqueous solution, and fitting the result to obtain a standard curve; (5) Extracting BaP and performing SERS detection: Dimethyl sulfoxide (DMSO) is added to the edible oil sample to extract the BaP therein, and then the BaP in the DMSO is stripped out using toluene. Finally, the sample is dried and redissolved before Raman detection. If a characteristic peak of BaP appears in the SERS spectrum, it indicates that the sample being tested contains BaP, and the concentration of BaP in the sample is quantitatively measured based on the standard curve obtained in step (4).

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

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

5. The method for detecting BaP in edible oil using CTAB-modified silver nanomaterials based on LLE-SERS according to claim 1, characterized in that: In the 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 using CTAB-modified silver nanomaterials based on LLE-SERS according to claim 1, characterized in that: 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.

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

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

1.

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

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