Research On The Detection Methods Of Food Borne Hazard Factors Based On Surface Enhanced Raman Spectroscopy

At present,due to the variety of food,food processing technologies and food processing steps,the risk of food pollution is increasing,so food safety has become an increasingly prominent social problem.There are many kinds of food borne hazard factors,including biological,chemical and physical hazard factors,and genetically modified food with potential hazard risks.How to detect the potential hazards in food quickly and effectively,and how to prevent the occurrence of food safety problems in time are of great significance to human health.In recent years,surface enhancement Raman spectroscopy（SERS）has been applied in food safety detection more and more frequently because of its advantages of high sensitivity,simple operation,high accuracy and no sample pretreatment.In this paper,several kinds of common Raman substrates and new membrane material-based Raman substrate were applied to establish the surface enhanced Raman detection method,and several representative food borne hazard factors were detected:（1）Preparation and study of surface enhanced Raman substratesThe precious metal nanoparticles such as gold nanoparticles（AuNPs）and silver nanoparticles（AgNPs）prepared in this chapter,due to their special surface characteristic,are the classic SERS substrate,however,each of them has advantages and disadvantages.AuNPs are relatively stable while the resonance intensity is not perfect;AgNPs has strong Raman enhancement effect,but its stability is poor,and it is easy to be oxidized.As a result,the bimetallic composite silver-gold core-shell structure（Au@Ag）has been widely used.The Raman signal enhancement effect of the above three kinds of particles were compared,and it was found that the Au@Ag has better enhancement effect.This kind of substrate not only maintains the characteristics of AuNPs,including uniform particle size,easy preparation,and good stability,but also combines the advantages of silver nanomaterials,such as ideal Raman enhancement effect.In addition,with the development of the Raman research,the non-metallic material SiO₂ nanospheres are often used as the core structure of Raman core-shell materials because of the virtue of simple synthesis,narrow particle size distribution and easy control of particle size.Ccompared with the traditional spherical or core-shell Raman substrate,the silver coated silica microsphere（SiO₂@Ag）has better Raman enhancement effect.In addition,a new Raman substrate based on the glass fiber membrane matrix was prepared,the Raman spectra of two kinds of signal molecules,CVa and MB were successfully obtained.Combined with the flexibility of glass fiber,the substrate has a good practical application potential.（2）Mercaptopyridine-functionalized metal nanoparticles for one-step surface enhancement Raman spectroscopy（SERS）Hg²⁺ sensingThe commonly SERS method for mercury ion detection mainly apply the T-Hg²⁺-T structure formed by mercury ion(Hg²⁺)and thymine（T）in a short DNA strand rich in T bases as an aptamer of Hg²⁺.In this case,the short DNA strand and Raman reporter molecule need to be assembled on the substrate at the same time,which is cumbersome.The detection method established in this chapter mainly uses 4-mercaptopyridine（4-Mpy）as the Raman reporter molecule,which is modified on the surface of AuNPs to prepare the detection sensor.Then,the N in the pyridine group can form the Hg-（pyridine）2 complex through the coordination of multivalent N bond and Hg²⁺,and the metal nanoparticles can be gathered together through the structure of 4-MPY-Hg-4-MPY forming hot spots,which can enhance the Raman signal intensity of 4-MPY.Then the positive correlation between the Raman intensity and the Hg²⁺ concentration was obtained,and the quantitative detection of Hg²⁺ was realized.At the same time,the detection sensitivity of the system prepared by AuNPs and Au@Ag core-shell structure is compared.It is found that the system prepared by Au@Ag core-shell structure has better Raman enhancement effect and improves the detection sensitivity.（3）Detection of nitrite by surface enhanced Raman spectroscopy based on core-shell substrate erosionNitrite is a common additive in food,which can effectively prevent the growth of bacteria and the oxidation of food,so it is often used as a food preservative.In addition,in the process of vegetable pickling,or when the leftovers are placed for too long,the concentrated nitrate will be reduced to nitrite in the fermentation process.When nitrite enters human blood,it is easy to cause hypoxia poisoning and even death.Besides,it may induce cancer.In this chapter,the Raman reporter molecule rhodamine 6G（Rho-6g）is modified on the surface of the Au@Ag core-shell nanoparticles first,then the system has strong Raman signal in the original state,and then the silver shell on the surface of the core-shell structure will be eroded by the mild oxidation of nitrite ion（NO2-）in the acidic condition,so that the Raman enhancement effect of the Raman system is reduced,then the negative correlation between Rho-6g signal intensity and NO₂^-concentration was established to realize the quantitative detection of nitrite.In addition,the detection sensitivity of AuNPs and SiO₂ which employed as Raman core-shell structure were compared,and SiO₂@Ag core-shell structure was found to be more sensitive.（4）Rapid detection of crystal violet residue in shrimp products by surface enhanced Raman spectroscopy based on glass fiber membrane substrateThere are some drug residues in fish,shrimp,and vegetables,fruits for the purpose of keeping fresh or avoiding diseases and insect pests.The traditional detection methods based on large-scale instruments will dilute the drug in the samples to a certain extent after sample preparation.If the detection sensitivity is limited,it can easily lead to the false-negative result.Moreover,some sample preparation methods are cumbersome and time-consuming.In view of this situation,a new type of Raman substrate was prepared in this chapter.Taking glass fiber membrane as the substrate,silver nanoparticles were grown in situ on it,and a membrane Raman substrate with good softness and homogeneity was obtained.This substrate is convenient for sampling on the surface of solid samples,and it will not cause the loss of analyte concentration in the samples.Analytes with low concentration at f M-level can also be detected.The CVa content in shrimp samples was successfully detected by using the prepared substrate.In addition,the detection of liquid samples was not affected by using this substrate,which could be detected through directly adding to the substrate or absorbing to the substrate by soaking.（5）In vitro isothermal nucleic acid amplification combined with surface-enhanced Raman spectroscopic（SERS）method for ultrasensitive detection of Vibrio parahaemolyticusDetection of pathogenic microorganisms is of great importance for public health and food safety.Traditional techniques can hardly meet the continuously increased demanding in sensitivity and specificity of pathogen detections methods.In this study,Vibrio parahaemolyticus（V.parahaemolyticus,VP）was used as the model analyte,and an antibody-Vp-aptamer hetero-sandwich based surface-enhanced Raman scattering（SERS）method was developed in conjunction with in vitro isothermal amplification for sensitive detection of VP.The rolling circular amplification（RCA）products provided enormous sites for assembling the Au@Ag nanoparticles and formed excess “hot-spot” sites for Raman measurement.By using this enhanced Raman signal strategy in the detection scheme,a limit of detection（LOD）as low as 1 cfu/m L was successfully achieved for ultrasensitive detection of V.parahaemolyticus.In addition,we have applied this scheme to artificially contaminated food samples.The detection data indicated that this method is able to determine the concentrations of V.parahaemolyticus in the spiked food samples with satisfactory sensitivity and specificity and thus,this developed ultrasensitive SERS scheme is well suited for the urgent need in pathogen detection and demonstrated great potential in food safety,environment monitoring,and clinical setting.（6）SERS-decoding: Simultaneous detection of multiple genetically modified organism（GMO）components on the same test line of lateral flow stripFacilitated one-step multiplex lateral flow strip（LFS）is increasingly needed for a variety of biochemical purposes.Herein,a surface-enhanced Raman scattering（SERS）-integrated LFS platform was developed for rapid and simultaneous determination of multiple genetically modified organism（GMO）components（promoter,codon,and terminator）of soybean.Experimental results demonstrated that,on the same test line（T line）of single LFS,the three different components can be determined simultaneously with the help of three different SERS nano tags,and good linear correlations between the Raman signal and concentration of each component were also obtained for quantitative analysis.Of greater importance,whether these multiple analytes coexisted or not,varied in the same concentration trend or not,these multiple analytes can be rapidly（within 15 min）and accurately detected with satisfied sensitivity and specificity by decoding the characteristic Raman peak signals on the same T line.We envision that the SERS decoding platform can further improve the potential of LFS and SERS for practical applications and provide a promising alternative for multiple screening.