Application Of Raman Spectroscopy In The Rapid Detection Of Food Packaging And Biological Contaminants

With the rapid development of economy,science and technology in China,consumers pay more attention to daily food safety issues derived from environmental contamination,agriculture and industrial production.At the same time,the better food quality is urgently needed because of the more diversified food culture.In China and even the whole world,foodborne illness by ingestion is the mainly food safety risks.As the main types of hazards,chemical and biological pollutants could be detected in professional laboratory by professional staffs,which is always tedious and time-consuming.In this thesis,we established a series of novel Raman biosensors with good sensitivity and high accuracy,which were constructed by surface-enhanced Raman scattering（SERS）of gold and silver nanostructured assemblies and isotope labelling-Raman microspectroscopy,for detection of the outstanding food hazards.These provided technical support for the protection of food safety.First,Au NPs（gold nanoparticle）and Au NRs（gold nanorod）were synthesized with good dispersity,stability and uniform distribution.SERS-encoded aptasensor based on Au NPs-Au NRs heteroassemblies were established by DNA hybridization,for the rapid detection of BPA.The Au NPs were connected on the ends of the Au NRs,by changing the charge coating on the ends and sides of the Au NRs with cetyl-trimethylammonium bromide and thiol-modified polyethylene glycol.SERS enhancement mainly results from the ends of Au NRs with a greater local field effect and the narrow gaps between the ends of the Au NRs and the Au NPs.The established SERS sensor had good practicability and could be used as a promising method for BPA detection with a linear range of 0.001-1 ng/mL,and a good linearity y=-616.69*lg（x）+282.35.A detection limit of 3.9 pg/mL and good specificity was obtained.Second,Au NRs and silver nanoparticles（Ag NPs）were synthesized.We established Au NRs core–Ag NPs satellite assemblies by two parts of DNA complementary sequences.The nanoparticles and core–satellite assemblies were characterized by transmission electron microscope and Raman spectra.The assembled structures were uniform and controllable,which are ideal SERS substrates.The impressively improved intensity of SERS was mainly from many in-built intense electromagnetic hot-spots among assemblies and greater local field effect of the ends of Au NRs.Therefore,these assemblies were used as an ultrasensitive aptamer-based SERS sensor with a wide linear range was of 0.005–1 fM and a LOD of 4.3amol/L.Third,Salmonella typhimurium（S.typhimurium）was incubated in tryptic soy broth media with different percentages of heavy water（D₂O）to obtain the optimum culture conditions.By combining D₂O labeling with Raman microspectroscopy,live or dead cells of S.typhimurium are distinguished.This was based on the characteristic Raman signals of deuterium incorporated S.typhimurium cells resulting from carbon–deuterium（C-D）vibration.The quantitation of S.typhimurium was obtained in 4 h,6 h and 8 h by the linearly relationship between the CD/（CD+CH）%（the percentage of Raman spectral intensity of the C-D over the sum of both C-D and C-H Raman spectral intensity）of S.typhimurium and the log value of the S.typhimurium concentration,with a linear range of 10²–10⁶ colony-forming unit（CFU）/mL and a LOD of 10² CFU/mL.Fourth,the total number of bacterial cells in food can be used to indicate the food contamination by foodborne microorganism.Above all,the applicability of incorporation of heavy water and Raman microspectroscopy sensor were evaluated by quantification of S.typhimurium,Escherichia coli and Staphylococcus aureus.Good linearly relationships between the log value of the bacterial concentrations and the CD/（CD+CH）%were obtained for different bacteria.Principal component analysis（PCA）was effectively used to distinguish S.typhimurium,E.coli and S.aureus.And as a food hygienic standard,aerobic bacterial count of milk was obtained by incorporation of heavy water and Raman microspectroscopy.Standard curve（Y=1.322 Log（x）-1.483）was derived between CD/（CD+CH）%and the total number of bacterial cells with a LOD of 10³ CFU/mL and excellent correlation coefficient of R²=0.9544.