Detection Of Nitrite In Zhenjiang Jellied Meat Using Surface Enhanced Raman Spectroscopy Technique

Zhenjiang jellied meat is popular with consumers due to their unique flavor and nutritional value.However,the process of producing Zhenjiang jellied meat requires nitrite,which is challenging to be removed afterward,as its potential carcinogenicity to the human body is well-established.Thus,this may raise the risk of nitrite content to exceed the maximum allowed permissible limit in jellied meat.Therefore,several chromatographic,electrochemical,electronic and fluorescence spectroscopic methods have been reported to precisely monitor the nitrite content in different matrices.However,there are many limitations and adequacies linked with the existing methods,precisely the detection speed,sensitivity and selectivity.Recently,surface-enhanced Raman spectroscopy（SERS）has attracted much attention in life sciences,food safety,environmental monitoring and national security mainly due to its simplicity,high sensitivity,selectivity and use in real-time.Hence,the current thesis extends the application of SERS to precisely monitor the concentration of nitrite in Zhenjiang jellied meat.The main study contents are as follows:1.Evaluating the nitrite detection mechanism using SERS based on 4-aminothiophenol（4-ATP）.4-ATP has been abundantly used in SERS research as a Raman active reporter molecule.However,the 4-ATP characteristic peaks are susceptible to be influenced by different experimental factors in the course of designing a SERS detection sensor.Hence,this chapter administer a complete portrayal of the physicochemical factors that controls the nature of 4-ATP such as the solvent effect,laser power,substrate,reaction medium and time,influence of air,oxygen and/or other related ions.The relative binding affinity of 4-ATP reaction mechanism and dissociation of nitrite was confirmed by electronic assignments and color patterns.Theoretically,the mechanism and nature of 4-ATP changes by nitrite in the process of its detection with 4-ATP,and the experimental conditions that may triggers 4-ATP to generate b₂SERS peaks(1142、1388 and 1432 cm^-1)have been thoroughly examined.Interestingly,under the optimized acidic conditions,the characteristic peaks of 4-ATP remains unaffected and withstand adequate variations in the laser power,substrate,reaction time,air and nature of the media.Colorimetric and electronic assignement were used to differentiate the4,4-dimercaptoazobenzene（DMAB）specie formed by its oxidation,self-ionization and/or dissociation,and diazenylbenzenethiol specie generated via mutual interaction between 4-ATP and nitrite.This research has shown that when the pH of 4-ATP solution is less than 2.0,the characteristic peaks of 4-ATP are stable,which provides a reliable and controlled pattern for the rapid detection of nitrite in Zhenjiang jellied meat based on SERS.2.Study on detecting nitrite in Zhenjiang jellied meat based on SERS technology.In order to solve the lower enhancement effect of the SERS substrate,a hollow zinc oxide silver（ZnO@Ag）nanosphere was synthesized.Polystyrene（PS）as a template was utilized for ZnO microsphere synthesis which was further transformed into a hollow geometry prior loading silver nanoparticles（AgNPs）on its framework.The synthesized hollow ZnO@Ag nanosphere was characterized by transmission electron microscopy（TEM）,field emission scanning electron microscopy（FESEM）,X-ray diffraction（XRD）,infrared and ultraviolet spectroscopies.The synthesized substrate was applied for resolving the lower sensitivity of the existing nitrite SERS sensor.The chemical interation of 4-ATP as diazo salt and 1-NA as the coupling agent was used to design a highly selective and sensitive detection system for nitrite ions.The results show that the Raman enhancement factor of the synthesized hollow ZnO@Ag nanospheres is 3.17×10⁸,and the method exhibited a wide linear range(1.0×10^-8-1.0×10^-3 mol L^-1)for nitrite with a lower limit of detection（LOD）0.3×10^-8 mol L^-1.The method was applied successfully for the analysis of nitrite in Zhenjiang jellied meat samples.The variations in the accuracy and precision of the data were re-confirmed with the input from the standard UV-Vis spectroscopy method（GB5009.33-2016）in terms of student t tests with no significant differences between the two methods.The research shows that the SERS sensor is accurate,sensitive and suitable for the trace levels detetermination of nitrite in Zhenjiang jellied meat samples.3.Rapid detection of nitrite in Zhenjiang jellied meat based on SERS combined with chemometrics.This chapter aims to generate a new on-site orientation by developing a rapid SERS platform for nitrite detection in real-time via its coupling with chemometric algorithms using a simple gold-silver core-shell nanoparticles（Au@Ag NPs）substrate.The substrate was synthesized by sequential reduction of chloroauric acid（HAuCl₄·4H₂O）,silver nitrate（AgNO₃）and characterized by TEM,high resolution（HRTEM）HRTEM),energy dispersive X-ray spectroscopy（EDS）and UV-Vis spectroscopy.Using the established sensor,the spectral data was collected and subjected to partial least squares（PLS）multivariate calibrations.The modeling results generated a correlation coefficients of calibration（R_c）0.967,root mean square error of cross-validation（RMSECV）0.426,correlation coefficients of prediction（R_P）0.9734 and the root mean square error of prediction（RMSEP）with a value 0.383.The method was applied successfully for the analysis of nitrite in Zhenjiang jellied meat samples.The applicability of the proposed SERS sensors was further validated by standard UV-Vis spectroscopy method.The study has shown that the established SERS sensor has accurate results,high sensitivity and might be suitable for the trace detection of nitrite in complicated food matrices.This thesis research on fabricating detection method for nitrite in Zhenjiang jelled meat.Theoretically and experimentally studied the factors that may cause 4-ATP characteristic peak to change.Then 1-NA was introduced for method building.Hollow zinc oxide silver nanosphere were synthesized as SERS substrates to achieve trace detection of nitrite.Finally,combined SERS with PLS realizes fast and highly sensitive detection of nitrite in Zhenjiang jelled meat.