Preparation method of Ag NPs (at) Aw NWs SERS (Surface Enhanced Raman Scattering) chip for detecting 2, 5-DMP (Dimethyl Phthalate) and method for monitoring quality of skipjack steak frying oil in real time

Abstract

The invention discloses a preparation method of an Ag NPs (at) Aw NWs SERS (Surface Enhanced Raman Scattering) chip for detecting 2, 5-DMP (Dimethyl Phthalate) and a method for monitoring the quality of skipjack steak frying oil in real time, and is characterized in that the preparation method of the chip comprises the following steps: 1) synthesizing AuNWs on a steel comb through an Au seed mediation method; (2) sputtering AgNPs on the Au NWs through magnetron sputtering to form an Ag NPs (at) Aw NWs SERS chip with an intestinal villus surface structure; a method for detecting the content of 2, 5-DMP in skipjack steak, skipjack steak frying oil and skipjack steak frying steam by utilizing an SERS chip is utilized, a linear relation between the concentration of 2, 5-DMP in the skipjack steak frying steam and the acid value and the total polar component content in the skipjack steak frying oil is further constructed, and the SERS chip is utilized for detecting the content of 2, 5-DMP in the skipjack steak frying steam. The method has the advantages that the SERS (Surface Enhanced Raman Scattering) intensity can be enhanced, and the sensitivity and the accuracy are high.

Description

Technical Field

[0001] The present invention relates to the detection of 2,5-DMP, and in particular to a preparation method of an AgNPs@Aw NWsSERS chip for detecting 2,5-DMP and a method for real-time monitoring of the quality of frying oil for bonito fillets. Background Art

[0002] Bonito (Katsuwonuspelamis) belongs to the family Scombridae and is an important part of the world's tuna fish. It has extremely high economic value among commercial fishes worldwide and is well-known for its wide geographical distribution and abundant production. Bonito is not only rich in nutritional value but also reasonably priced, so it is often processed into various foods such as sashimi and canned food. In order to cater to the taste preferences of contemporary consumers, deep-fried bonito fillets made by deep-frying technology are widely favored by consumers because of their crispy skin and rich aroma, becoming a traditional specialty product with unique flavor in the category of pre-prepared aquatic products. During the frying process, the fish fillets not only produce an attractive fried flavor, effectively masking their inherent sourness and fishy smell, but also significantly improve in color, texture, flavor and taste. Bonito fillets catalyze the Maillard reaction and lipid oxidation reaction during high-temperature frying, thereby producing a large number of volatile flavor compounds. In the study of the aroma chemistry of fried foods, pyrazine compounds are generally considered to be the main components of the aroma and are closely related to the flavor quality of fried foods. 2,5-Dimethylpyrazine (2,5-DMP) can bring a unique and pleasant nutty and toasty flavor to deep-fried bonito fillets. 2,5-DMP has a very low olfactory threshold and can produce a significant olfactory effect even at very low concentrations, so it is considered an important indicator of flavor quality during deep-fried bonito fillets processing.

[0003] However, traditional frying processes often lack scientific standards and rely on empiricism, resulting in unstable product quality. Oil quality changes are mainly based on conventional indicators such as acid value (AV) and total polar component content (TPC). The detection experimental conditions of AV and TPC are harsh, the operation is cumbersome and time-consuming, and they are not suitable for on-site real-time monitoring. Therefore, it is crucial to develop an ideal detection technology to monitor the quality indicators of fried bonito fillets and frying oil in real time. Existing, gas chromatography (GC) or gas chromatography-mass spectrometry (GC-MS) technology is mainly used for qualitative and quantitative analysis of 2,5-DMP substances. However, in practical applications, these detection technologies have some limitations, including complex instrument operation procedures, cumbersome sample pretreatment steps, high dependence on professional technicians, and insufficient portability. Therefore, they are not suitable for real-time monitoring of key volatile substances such as 2,5-DMP during food processing. In contrast, surface enhanced Raman scattering (SERS) technology, as a non-destructive detection method, exhibits the characteristics of rapidity, high sensitivity, high reliability and excellent specificity in molecular-level detection and characterization. At present, there are no related research reports on real-time monitoring of bonito fillet frying oil quality based on Raman spectroscopy at home and abroad. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing an Ag NPs@AwNWs SERS chip for detecting 2,5-DMP, which can enhance the SERS intensity, and has high sensitivity and accuracy, and a method for real-time monitoring of the quality of frying oil for bonito fillets.

[0005] The technical solution adopted by the present invention to solve the above technical problems is: a method for preparing an Ag NPs@Aw NWs SERS chip for detecting 2,5-DMP, comprising the following steps:

[0006] (1) AuNWs were synthesized on a steel comb by Au seed-mediated method;

[0007] (2) Ag NPs were directly sputtered on the AuNWs of the steel comb by magnetron sputtering and deposited for 10-20s to form the AgNPs@AwNWs SERS chip with the surface structure of intestinal villi.

[0008] Furthermore, the specific process of step (1) is as follows: the steel comb is pretreated with oxygen plasma for 10 minutes to improve the surface hydrophilicity, and then the surface of the steel comb is amino-functionalized by reacting with 0.1vt% APTES solution for 2 hours and then dried for use; after the steel comb is immersed in Au seed colloid solution for 2 hours, it is rinsed with water twice to remove excess Au seeds, and then the steel comb adsorbed with Au seeds is immersed in a reaction solution containing 7mM ligand 4-MBA, 17mg / mL HAuCl4 and 3.5mg / mL L-AA for growth for 30 minutes, thereby obtaining AuNWs vertically grown on the steel comb.

[0009] Furthermore, the preparation method of the Au seed colloidal solution is as follows: 19.7 μL of 100 mg / mL HAuCl4 solution is added to 20 mL of pure water under strong magnetic stirring, and then 100 μL of 14.7 mg / mL sodium citrate solution is added, and stirring is maintained for 2 to 3 minutes until the mixed solution changes from slightly yellow to clear and transparent; 600 μL of 3.783 mg / mL sodium borohydride solution is quickly added to the stirring mixed solution, and it is observed that the solution immediately changes from colorless to reddish brown. After stirring for 10 to 15 minutes, it is allowed to stand for 2 to 5 hours to obtain a stable Au seed colloidal solution.

[0010] The present invention also provides a method for detecting the content of 2,5-DMP in bonito fillets using the AgNPs@AwNWs SERS chip obtained by the above-mentioned preparation method, which is characterized by the following steps: directly inserting the SERS chip into a fried bonito fillet sample, then taking it out for SERS analysis, and calculating the concentration of 2,5-DMP in the bonito fillet to be tested based on the linear relationship between the 2,5-DMP concentration and the SERS intensity in the solid model.

[0011] The present invention also provides a method for detecting the content of 2,5-DMP in bonito fillet frying oil using the Ag NPs@Aw NWs SERS chip obtained by the above-mentioned preparation method, the steps of which are as follows: immersing the SERS chip in the bonito fillet frying oil sample, taking it out after sufficient contact, and performing SERS analysis; according to the linear relationship between the 2,5-DMP concentration and the SERS intensity in the liquid model, the concentration of 2,5-DMP in the bonito fillet frying oil to be tested is calculated.

[0012] The present invention also provides a method for detecting the content of 2,5-DMP in the frying steam of bonito fillet using the Ag NPs@Aw NWs SERS chip obtained by the above preparation method, the steps of which are as follows: fixing the SERS chip in an electric fryer at a position 10 cm away from the surface of the frying oil, incubating for 10 minutes, taking out for SERS analysis, and calculating the concentration of 2,5-DMP in the frying steam of the bonito fillet to be tested based on the linear relationship between the 2,5-DMP concentration in the saturated 2,5-DMP steam and the SERS intensity.

[0013] The present invention also provides a method for real-time monitoring of the quality of bonito fillet frying oil using the Ag NPs@Aw NWs SERS chip obtained by the above preparation method, the steps of which are as follows: respectively constructing a linear relationship between the 2,5-DMP concentration in the bonito fillet frying steam and the acid value and total polar component content in the bonito fillet frying oil, and using the SERS chip to detect the 2,5-DMP content in the bonito fillet frying steam to monitor the changes in the acid value and total polar component content in the bonito fillet frying oil in real time.

[0014] Compared with the prior art, the advantages of the present invention are:

[0015] 1. The SERS chip is designed with a steel comb with multiple teeth, which not only ensures full contact with the solid phase tissue, but also the villi-like Au NWs proliferated on the comb teeth form a structure with a large specific surface area, which is convenient for adsorbing the molecules to be measured in the liquid and gas phases. The Au NWs substrate in the SERS chip has a larger surface area and higher loading capacity, and the Ag NPs improve the performance of SERS and promote the interaction between the target molecules and the Raman "hot spots". This structure can adsorb and anchor the target molecules, thereby improving the sensitivity of the Raman detection method.

[0016] 2. The Ag NPs@AwNWs SERS chip based on the surface structure of intestinal villi was used to detect 2,5-DMP in the three-phase system of fried solid phase (fried bonito fillet), liquid phase (fried oil) and fried gas phase (fried steam). The detection limit (LOD) values ​​of 2,5-DMP in the three systems were found to be 6.0×10 -9 M, 1.82×10 -7 mg / mL, and 331ppt, which fully demonstrated that the substrate could successfully capture 2,5-DMP substances in complex systems.

[0017] 3. The deterioration of frying oil during the processing is an important factor affecting the food safety of fried fish fillets. The conventional indicators for detecting oil quality are mainly TPC and AV. By detecting the SERS intensity value of 2,5-DMP in frying steam, it can replace the detection indicators such as TPC and AV. It can not only simplify the oil detection process, but also accurately grasp the dynamic changes of oil quality during the frying process. It can be used as an efficient monitoring method for real-time monitoring of the quality and safety of fried fish fillets.

[0018] In summary, the preparation method of the Ag NPs@Aw NWs SERS chip for detecting 2,5-DMP and its application can monitor the change of 2,5-DMP content in the solid-liquid-gas three-phase system of fried bonito fillets in real time, and determine the degree of frying oil deterioration by monitoring the SERS intensity of 2,5-DMP in the frying gas phase (frying steam), thereby replacing the traditional oil detection indicators. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a working principle diagram of real-time monitoring of the quality of frying oil for bonito fillet based on Raman spectroscopy;

[0020] Figure 2 is the SEM image of Au seeds, and the inset is the particle size distribution of Au seeds;

[0021] Figure 3 is the SEM image of AuNWs, and the inset is the particle size distribution of Au NWs;

[0022] Figure 4 SEM image of AgNPs@AwNWs on the surface structure of intestinal villi;

[0023] Figure 5 The actual picture and partial magnified picture of the AgNPs@AwNWs SERS chip on the surface structure of intestinal villi;

[0024] Figure 6 The SERS chip is used to detect 2,5-DMP in the solid phase, where (a) is a solid phase model, which is used as a standard for detecting the content of 2,5-DMP in the solid phase system; (b) is a solid phase model with different concentrations of 10 -3 -10 -8 SERS spectrum of 2,5-DMP of M; (c) 865cm in the solid phase system -1 The concentration-response semi-logarithmic curve of 2,5-DMP at (d) is the characteristic peak of 2,5-DMP at 865 cm -1 Correlation analysis of SERS intensity at and frying batches (0-40h);

[0025] Figure 7 The SERS chip is used to detect 2,5-DMP in the solid phase, where (a) is a liquid phase model, which is used as a standard for detecting the content of 2,5-DMP in the liquid phase system; (b) is a liquid phase model with different concentrations of 10 -3 -10 -8 SERS spectrum of 2,5-DMP of M; (c) 865cm in liquid system -1 The concentration-response semi-logarithmic curve of 2,5-DMP at (d) is the characteristic peak of 2,5-DMP at 865 cm -1 Correlation analysis of SERS intensity at and frying batches (0-40h);

[0026] Figure 8 The SERS chip is used to detect 2,5-DMP in the gas phase, where (a) is the gas phase model, which is used as a standard for detecting the content of 2,5-DMP in the solid phase system; (b) is the gas phase model with different concentrations of 10 -3 -10-8 SERS spectrum of 2,5-DMP of M; (c) 865cm in the gas phase system -1 The concentration-response semi-logarithmic curve of 2,5-DMP at (d) is the characteristic peak of 2,5-DMP at 865 cm -1 Correlation analysis of SERS intensity at and frying batches (0-40h);

[0027] Fig. 9 is the change curve of AV and TPC content in frying oil with the increase of frying batches;

[0028] Fig.10 This is the correlation analysis between the SERS intensity change of 2,5-DMP and AV in the fried three-phase system. In the figure, Steaks, oil, and steam represent the SERS intensity of 2,5-DMP in the fried solid (fried bonito fillet), liquid (fried oil), and gas (fried steam) three-phase system, respectively. Steaks+oil+steam represents the sum of the SERS intensity of 2,5-DMP in the fried solid-liquid-gas three-phase system, and Steaks+steam represents the sum of the SERS intensity of 2,5-DMP in the fried solid-gas three-phase system.

[0029] Fig.11 The correlation analysis between the SERS intensity change of 2,5-DMP and TPC in the three frying systems is shown;

[0030] Fig.12 SERS spectra of Au NWs substrates synthesized for different concentrations of ligand 4-MBA (1, 4, 7, and 10 mM);

[0031] Fig.13 The Au NWs substrate synthesized with the same concentration of 4-MBA (1, 4, 7 and 10 mM) at 1620 cm -1 Comparison results of characteristic peak signal intensity values ​​at ; DETAILED DESCRIPTION

[0032] The present invention is further described in detail below with reference to the accompanying drawings.

[0033] Reagents: Chloroauric acid (HAuCl4·xH2O, 99.9%), 3-aminopropyltriethoxysilane (APTES, 99%), and 4-mercaptobenzoic acid (4-MBA, 90%) were purchased from Aladdin. Sodium citrate (C6H5Na3O7, 99.8%) and sodium borohydride (NaBH4) were purchased from SigmaAldrich. L-AA and Raman molecule crystal violet CV were purchased from Sinopharm Chemical Reagent Co., Ltd. 2,5-Dimethylpyrazine standards and gel were purchased from Shanghai MacLean Biochemical Co., Ltd. Raw bonito fillet was provided by Ningbo Jinri Food Co., Ltd. Soybean oil, steel comb, and electric fryer were purchased from a local supermarket in Ningbo. All chemical reagents used were analytical grade, and deionized water (18.2 MΩ·cm) was used.

[0034] Instruments: The surface hydrophilicity was modified by a low-pressure plasma system (Zepto, Diener, vacuum pressure: 15Pa, radio power: 30W). The morphological structure image of the substrate was measured by a field emission scanning electron microscope (SEM, SU-70, Hitachi, secondary electron mode) at a voltage of 5kV. The elemental composition and distribution of the substrate were recorded using an energy dispersive spectrometer (EDS, EDAX TEAMApolloXL) and elemental mapping. The crystal structure of the prepared substrate was detected using an X-ray diffractometer (XRD, D8ADVANCE, Brucker) and a CU-Kα radiation source at 2θ of 5-80°. The SERS signal was measured by a Raman spectrometer (BWS 415, B&W TekInc.) equipped with a 785nm semiconductor laser, with an integration time of 10s and a laser power of 20mW. 1. Specific embodiments

[0036] A method for preparing an AgNPs@AwNWs SERS chip based on the surface structure of intestinal villi, comprising the following steps:

[0037] 1. AuNWs were synthesized by Au seed-mediated method, e.g. Figure 1 Shown

[0038] (1) Preparation of Au seed colloidal solution: First, at room temperature, 19.7 μL of 100 mg / mL HAuCl4 solution was added to 20 mL of pure water under strong magnetic stirring, followed by 100 μL of 14.7 mg / mL sodium citrate solution. The mixture was stirred for 2 to 3 minutes until the color of the mixture changed from slightly yellow to clear and transparent. 600 μL of 3.783 mg / mL sodium borohydride solution was quickly added to the stirred mixture, and the solution was observed to immediately change from colorless to reddish brown. After stirring for 10 to 15 minutes, the mixture was allowed to stand for 2 to 5 hours to allow the nanoparticles to age and obtain a stable Au seed colloidal solution. Figure 2The figure shows the SEM image of Au seeds, and the inserted figure shows the particle size distribution of Au seeds. It can be seen that the average particle size of Au seeds is 11.44±6.19nm.

[0039] (2) To prepare vertical Au NWs on the steel comb, the material (about 2 cm) was first exposed to O2 plasma. 2 ) for 10 minutes to improve the surface hydrophilicity. Then, by reacting with APTES solution (0.1% v / v) for 2 hours, the material surface was functionalized with amino groups and dried for use. The Au NPs colloid was then transferred to a clean glass bottle, and the steel comb was immersed in the AuNPs colloid solution for 2 hours to ensure the adsorption of AuNPs, and rinsed with water twice to remove excess Au seeds. The Au seed-adsorbed steel comb was then immersed in a reaction solution containing 7mM ligand 4-MBA, 17mg / mL HAuCl4 and 3.5mg / mL L-AA for 30 minutes of growth; after the reaction, it was washed with ethanol to prepare Au NWs vertically grown on the steel comb and dried. Figure 3 is the SEM image of Au NWs, and the inserted figure is the particle size distribution of Au NWs. It can be seen that the average particle size of AuNWs is 20.43±4.27nm.

[0040] 2. AgNPs were directly sputtered on the Au NWs of the steel comb by magnetron sputtering and deposited for 10-20s to form the AgNPs@AwNWs SERS chip with the surface structure of intestinal villi.

[0041] Figure 4 The SEM image of Ag NPs@AwNWs on the surface structure of intestinal villi shows that Ag NPs have been successfully deposited on AuNWs, and the binary composite substrate is completed.

[0042] Figure 5 Actual picture and partial enlarged picture of the Ag NPs@AwNWs SERS chip of the surface structure of intestinal villi.

[0043] 2. Application Examples

[0044] Based on the Ag NPs@Aw NWs SERS chip with the surface structure of intestinal villi prepared in Example 1, real-time detection of the change trend of 2,5-DMP substance during the frying process of bonito fillet was established to establish a Raman detection method for monitoring the quality change of frying oil

[0045] 1. SERS detection of 2,5-DMP in solid phase

[0046] An equal amount of gel was added to a standard solution containing different concentrations of 2,5-DMP (the solution prepared by mixing the purchased gel with different concentrations of 2,5-DMP was heated in a water bath and added to a square mold for gelation). After gelation, a solid model containing different concentrations of 2,5-DMP was obtained, such as Figure 6 As shown in (a). The tip of the prepared AgNPs@Au NWs SERS substrate chip based on the surface structure of intestinal villi was inserted into the model gel, incubated for 10 minutes, and then taken out for SERS analysis. The model was used as a standard for detecting the content of 2,5-DMP in the solid phase, and a standard curve for detecting 2,5-DMP was established. Figure 6 As shown in (b), the concentration of 2,5-DMP was increased from 10 -3 M was diluted to 10 -8 M, the SERS spectrum intensity also decreases accordingly. -8 M, a clear SERS signal can still be observed. Figure 6 (c) Further shows the logarithm of the concentration of 2,5-DMP and the characteristic peak 865 cm -1 Calibration curve of SERS intensity at 2 The value was as high as 0.993. Therefore, the detection limit (LOD) of 2,5-DMP in the solid phase was finally determined to be 6.0×10 -9 M, which proves that the SERS chip has excellent SERS quantitative detection ability for 2,5-DMP in the solid phase.

[0047] The actual production process of deep-fried bonito fillets in a factory was simulated, and the sampling interval was set to 1 hour during the continuous frying process. After frying the bonito fillets, they were taken out of the electric fryer and placed on a stainless steel sieve to drain the excess oil on the surface. The SERS chip was then directly inserted into the deep-fried bonito fillet sample and subsequently taken out for SERS analysis to determine the concentration of 2,5-DMP in different fried batches of bonito fillets. Figure 6 (d) as shown, at 865cm -1 The characteristic peak is at , and the correlation curve between the frying batch and the characteristic peak intensity is plotted. It can be seen that with the increase of frying batches, the content of 2,5-DMP generally increases, and the content increases rapidly in the early stage of frying. After frying for 20 hours (200 batches), the content of 2,5-DMP in fried fish fillets tends to be stable.

[0048] 2. SERS detection of 2,5-DMP in liquid phase

[0049] like Figure 7As shown in (a), soybean oil was mixed with 2,5-DMP standard solutions of different concentrations as a liquid model. The SERS chip was then immersed in the liquid model and incubated for 10 min. The SERS chip was then taken out for SERS detection, and a standard curve of 2,5-DMP content in the liquid phase was established. Figure 7 (b) shows the SERS spectra of 2,5-DMP in soybean oil with a concentration range of 1.00–1.08×10 -6 mg / mL. The characteristic peak is 865cm -1 A general trend can be observed that the intensity of the SERS signal increases with the enrichment of 2,5-DMP. -1 The calibration curve of SERS intensity at 2,5-DMP concentration in liquid phase is shown in Figure 7 (c) shows a good linear relationship, R 2 The final LOD value is 1.82×10 -7 mg / mL, which proves that the SERS chip can also be used to quantitatively detect 2,5-DMP in liquid phase with very high sensitivity.

[0050] In the actual frying production process, the detection of 2,5-DMP content in the frying oil liquid phase is carried out at an interval of 1 hour. Take out 5mL of frying oil from the electric fryer and immerse the SERS chip in the frying oil. After sufficient contact with the frying oil sample, the SERS detection of 2,5-DMP content is carried out to determine the concentration of 2,5-DMP in frying oil of different frying batches. Figure 7 (d) as shown, at 865cm -1 The characteristic peak is shown at , and the correlation curve between the frying batch and the characteristic peak intensity is plotted. It can be seen that with the increase of frying batches, the content of 2,5-DMP in the frying oil gradually increases as a whole, and tends to be stable after frying for 20 hours (200 batches).

[0051] 3. SERS detection of 2,5-DMP in gas phase.

[0052] like Figure 8As shown in (a), a gas phase model is established for SERS detection of 2,5-DMP in the gas phase. First, 5 mL of a 2,5-DMP standard solution of known concentration is poured into a 10 mL sealed bottle, and then heated on a heating plate at 200°C for 5 minutes to accelerate the release of gaseous 2,5-DMP to the top of the sealed bottle. A certain amount of saturated 2,5-DMP vapor is then extracted from the top of the sealed bottle with a syringe and injected into a quartz window test chamber equipped with a SERS chip (the quartz window is the channel for incident light and Raman laser). The SERS chip is incubated for 30 minutes to adsorb sufficient 2,5-DMP vapor. Finally, the Raman laser is irradiated onto the SERS chip through the quartz window for in situ SERS detection, and a detection standard curve for 2,5-DMP in the gas phase is established. After SERS detection, Figure 8 (b) It can be seen that the gaseous 2,5-DMP of different concentrations is at 865 cm -1 A highly identifiable 2,5-DMP Raman peak is shown at 865 cm -1 The calibration curve of the average intensity of the SERS signal at 2,5-DMP as a logarithmic function of the concentration of 2,5-DMP is shown in Figure 8 (c) It shows a good linear relationship, R 2 The value is 0.992, and the final LOD value is 331ppt. This shows that the SERS chip has stable and sensitive detection performance for trace gaseous 2,5-DMP.

[0053] In the actual frying process, the concentration of 2,5-DMP in the frying steam was detected using a SERS chip, which was fixed in the electric fryer 10 cm away from the frying oil surface. Every hour, the chip was taken out for SERS detection to achieve real-time monitoring of the 2,5-DMP content in the frying steam. Figure 8 (d) as shown, at 865cm -1 The characteristic peak is shown in Figure 3. The correlation curve between the frying batch and the characteristic peak intensity is plotted. It can be seen that in the early stage of frying, the 2,5-DMP content in the frying steam increases slowly. After frying for 20 hours (200 batches), the 2,5-DMP content shows an exponential growth pattern.

[0054] 4. Establish a Raman detection method for monitoring changes in frying oil quality

[0055] The change of oil quality is mainly based on conventional indicators such as acid value (AV) and total polar component content (TPC). In this patent, the AV and TPC values ​​measured in different frying batches of fried bonito fillets are used to establish a correlation analysis with the Raman intensity change value of 2,5-DMP in the frying solid-liquid-gas three-phase system. The good linear relationship obtained proves that the conventional frying quality indicators can be replaced by detecting the content of 2,5-DMP. Fig. 9This is a trend chart of the change of TPC content and AV with the increase of frying batches. With the increase of frying batches, the increase rate of these two values ​​is also accelerating. According to GB 2716-2018, once the TPC content of edible oil exceeds 27%, or the AV exceeds 5mg KOH / g, it should be discarded. Therefore, the TPC and AV in this study reached the limit at 34h and 32h of frying, respectively, so the safe use limit of frying oil can be determined as 32h (320 batches). In this study, by performing correlation analysis on the AV and TPC values ​​detected by conventional methods under the same frying batch, and the Raman intensity values ​​of 2,5-DMP in the three frying phases detected by SERS technology, it was concluded that the SERS intensity change of 2,5-DMP in the frying solid phase or liquid phase is nonlinearly related to TPC and AV, while the SERS intensity of 2,5-DMP in the gas phase is extremely linear with the changes in these two values, R 2 The values ​​are all 0.992. Fig.10 It shows the correlation analysis diagram of AV and 2,5-DMP in solid, liquid and gas respectively. Fig.11 It represents the correlation analysis diagram of TPC and 2,5-DMP in solid, liquid and gas respectively.

[0056] Therefore, based on the SERS chip constructed in this study, SERS real-time monitoring of 2,5-DMP in the frying gas phase (frying vapor) in fried bonito fillets can replace the traditional TPC and AV detection methods to determine the deterioration of frying oil during the frying process, thereby ensuring the edible safety of fried bonito fillets.

[0057] 3. Comparative Analysis of Experimental Results

[0058] 1.2,5-DMP SERS detection conditions optimization

[0059] The concentration of the ligand 4-MBA is crucial for the morphology of Au seeds growing into AuNWs. Therefore, we adjusted the concentration of 4-MBA to 1, 4, 7, and 10 mM to select the best morphology during the growth of AuNWs.

[0060] When the concentration of 4-MBA was reduced from 7mM to 4mM, the resulting gold nanostructures were short-toothed and the average diameter increased from 20.43nm to 33.21nm. When further reduced to 1mM, the Au seeds were deposited on the crystals and exhibited a nearly spherical growth pattern without any signs of line formation. In contrast, high concentrations of 4-MBA (10mM) resulted in excessive growth of Au NWs and the formation of stratified and uneven surfaces due to their dispersed stacking. Only when the 4-MBA concentration was 7mM did the Au NWs achieve complete growth and form a tightly packed intestinal villus structure. Crystal violet (CV) was used as a standard molecule to determine the SERS performance of Au NWs grown under different concentrations of the ligand 4-MBA. By verifying the SERS performance of Au NWs grown with different concentrations of 4-MBA, it was found that when the 4-MBA concentration was 7mM, the micromorphology of Au NWs was the best and the SERS performance was the strongest. This concentration can be used as the optimal ligand concentration for Au NWs, such as Fig.12 and Fig.13 As shown, this concentration can be used as the optimal ligand concentration for gold nanoparticles.

[0061] 2. The accuracy of SERS detection of 2,5-DMP in different frying object systems.

[0062] (1) In order to verify the accuracy of the obtained solid phase standard curve, raw bonito fillet samples were spiked with 10 -5 , 10 -6 and 10 -7 The recovery rate experiment was carried out using a 2,5-DMP standard solution of 1 M.

[0063] Table 1 Recovery rate of raw bonito fillet samples (n=5)

[0064]

[0065]

[0066] SD, standard deviation, n=5.

[0067] The test results are shown in Table 1. The 2,5-DMP content detected on the SERS chip is very close to the spiked concentration, and the recovery rate is between 94.40% and 98.92%, and the RSD is between 2.59% and 3.92%.

[0068] (2) In order to further verify the accuracy and effectiveness of this method in a liquid phase system, fresh soybean oil samples were added with 10 -3 , 10 -4 and 10 -5 mg / mL 2,5-DMP standard solution.

[0069] Table 2 Recovery rate of fresh soybean oil (n=5)

[0070]

[0071] SD, standard deviation, n=5.

[0072] As shown in Table 2, in this experiment, the SERS chip was used to perform SERS detection on 2,5-DMP, and the detected amount was closely related to the spiked concentration. The recovery rate was between 97.51% and 100.74%, and the RSD was between 2.30% and 3.33%, which confirmed that the SERS detection method established for liquid phase was accurate and effective.

[0073] In summary, the present invention has developed an Ag NPs@Au NWs SERS chip based on the surface structure of intestinal villi to monitor the content change of 2,5-DMP in the fried solid-liquid-gas three-phase system in real time with the increase of frying batches. The intestinal villi-shaped AgNPs@Au NWs SERS chip was used to monitor the content change of 2,5-DMP in the solid, liquid and gas during the processing of fried bonito fillets using surface Raman spectroscopy. The enhancement factor (EF) of the successfully prepared SERS chip reached 1.161×10 8 , showing excellent SERS performance with superior uniformity and reproducibility. Through SERS detection analysis, the detection limits of 2,5-DMP in solid phase, liquid phase and gas phase were 6.0×10 -9 M,1.82×10 -7 mg / mL, and 331ppt. During the processing of fried bonito fillets, the content of 2,5-DMP in the three-phase frying system increased with the increase of frying batches. Among them, the growth rate was the fastest in the frying steam system, and after frying for 20 hours, it showed an exponential growth trend. In the three-phase frying system, the change of 2,5-DMP content was positively correlated with the quality indicators of frying oil (total polar components and acid value), especially in the frying steam system, R 2 The values ​​of the SERS substrate chip based on the surface structure of intestinal villi were all 0.992, indicating that the fitting was highly reliable. Therefore, the SERS substrate chip based on the surface structure of intestinal villi developed in this study provides an effective technical means for monitoring the dynamic changes of 2,5-DMP content and frying oil quality.

[0074] The above description is not intended to limit the present invention, and the present invention is not limited to the above examples. Any changes, modifications, additions or substitutions made by a person skilled in the art within the spirit and scope of the present invention shall also fall within the protection scope of the present invention.

Claims

1. A method for preparing an Ag NPs@AwNWs SERS chip for detecting 2,5-DMP, characterized in that The following steps are involved: (1) AuNWs were synthesized on a steel comb by Au seed-mediated method; (2) Ag NPs were directly sputtered on the AuNWs of the steel comb by magnetron sputtering and deposited for 10-20s to form the AgNPs@AwNWs SERS chip with the surface structure of intestinal villi.

2. The method for preparing the Ag NPs@AwNWs SERS chip for detecting 2,5-DMP according to claim 1, characterized in that The specific process of step (1) is as follows: the steel comb is pretreated with oxygen plasma for 10 minutes to improve the surface hydrophilicity, and then the surface of the steel comb is amino-functionalized by reacting with 0.1vt% APTES solution for 2 hours and then dried for use; after the steel comb is immersed in the Au seed colloid solution for 2 hours, it is rinsed with water twice to remove excess Au seeds, and then the steel comb adsorbed with Au seeds is immersed in a reaction solution containing 7mM ligand 4-MBA, 17mg / mLHAuCl4 and 3.5mg / mL L-AA for growth for 30 minutes, thereby obtaining AuNWs vertically grown on the steel comb.

3. The method for preparing the Ag NPs@Aw NWs SERS chip for detecting 2,5-DMP according to claim 2, characterized in that The preparation method of the Au seed colloidal solution is as follows: 19.7 μL of 100 mg / mL HAuCl4 solution is added to 20 mL of pure water under strong magnetic stirring, and then 100 μL of 14.7 mg / mL sodium citrate solution is added, and stirring is maintained for 2 to 3 minutes until the mixed solution changes from slightly yellow to clear and transparent; 600 μL of 3.783 mg / mL sodium borohydride solution is quickly added to the stirring mixed solution, and it is observed that the solution immediately changes from colorless to reddish brown. After stirring for 10 to 15 minutes, the solution is allowed to stand for 2 to 5 hours to obtain a stable Au seed colloidal solution.

4. A method for detecting the content of 2,5-DMP in bonito fillet using the Ag NPs@Aw NWs SERS chip obtained according to any one of the preparation methods of claims 1 to 3, characterized in that The steps are as follows: the SERS chip is directly inserted into the fried bonito fillet sample, and then taken out for SERS analysis. Based on the linear relationship between the 2,5-DMP concentration and the SERS intensity in the solid model, the concentration of 2,5-DMP in the bonito fillet to be tested is calculated.

5. A method for detecting the content of 2,5-DMP in frying oil of bonito fillet using the Ag NPs@Aw NWs SERS chip obtained according to any one of the preparation methods of claims 1 to 3, characterized in that The steps are as follows: immerse the SERS chip in the bonito fillet frying oil sample, take it out after full contact, and perform SERS analysis. According to the linear relationship between the 2,5-DMP concentration in the liquid model and the SERS intensity, the concentration of 2,5-DMP in the bonito fillet frying oil to be tested is calculated.

6. A method for detecting the content of 2,5-DMP in frying steam of bonito fillet using the Ag NPs@Aw NWs SERS chip obtained by the preparation method according to any one of claims 1 to 3, characterized in that The steps are as follows: fix the SERS chip in the electric fryer at a position 10 cm away from the frying oil surface, incubate for 10 minutes, take out for SERS analysis, and calculate the concentration of 2,5-DMP in the frying steam of the bonito fillet to be tested based on the linear relationship between the 2,5-DMP concentration in the saturated 2,5-DMP vapor and the SERS intensity.

7. A method for real-time monitoring of the quality of frying oil for bonito fillet using the Ag NPs@AwNWs SERS chip obtained by the preparation method according to any one of claims 1 to 3, characterized in that The steps are as follows: construct a linear relationship between the 2,5-DMP concentration in the frying steam of bonito fillet and the acid value and total polar component content in the frying oil of bonito fillet, and use a SERS chip to detect the content of 2,5-DMP in the frying steam of bonito fillet to monitor the changes in the acid value and total polar component content in the frying oil of bonito fillet in real time.

Images