Research And Development Of Surface Enhanced Raman Scattering And Its Application To Food Safety

In the last three decades, a great deal of interest has been directed toward the development of active substrates for surface-enhanced Raman scattering(SERS) experiments. It has been already reported that SERS can be used for detection of traces amount of substances for a large variety of molecules of environmental and pharmaceutical interest. Metal(Au and Ag) nanoparticles have been the most commonly used Surface enhanced Raman Scatter substrates because of their special optical and electrical properties. In this master dissertation, the research and development of Surface Enhance Raman Scatter(SERS) substrate(especially Au and Ag nanoparticles) and its application to food safety is the main content, which is introduced by three parts.Firstly, various kinds of Au and Ag NPs(Au nanosphere, Ag nanosphere, Au nanorods, Ag nanowires) had been prepared. Then they were characterized by Ultraviolet-visible(UV-vis) absorbance spectra and Scanning Electron Microscope(SEM)Next, Ag and Au nanoparticles SERS activities had been studied in detail. We selected a type of Ag nanosphere with controllable morphology to investigate their SERS activity, meanwhile specially studied the effect of surface morphology and the nature of the metal-ligand interaction between probe molecules and the nanoparticles. Their SERS activities had been investigated by using Rhodamine 6G and Nile Blue A(NBA) as probe molecules. Differences in SERS enhancement were observed for Au and Ag nanoparticles with different morphology. Ag nanoparticles with nanosphere exhibited the highest SERS activity using NBA as probe molecules. The results demonstrated that this type of Ag nanosphere were SERS-active substrates, exhibiting much higher SERS activity than that of other shapes Au and Ag nanoparticles.Finally, a fast, sensitive and convenient method for on-site separation, identification and determination of organophosphate pesticide methidathion in tea leaves was reported, by the use of thin layer chromatography(TLC) in combination with surface-enhanced Raman spectroscopy(SERS). Five different organophosphate pesticides have been successfully separated and identified. Factors that affect the SERS detection sensitivity of methidathion, such as brand of TLC plates, material and concentration of metallic nanoparticles(NPs), have been examined. It is found that the limit of quantification for methidathion is 0.1 ppm. Spiked tea samples of different kinds and brands containing ppm level methidathion have been tested, with recovery rates among 86~113%. The TLC-SERS technologywas applied to rapid detection of malachite green and crystal violet contained in water samples. Employing the characteristic peaks and their intensity, qualification and quantification of MG and CV can be accomplished with the detection limit of 10μg/L, 50μg/L respectively. The proposed method for fast on-site determination of pesticide, malachite green(MG) and crystal violet(CV) may help to address the food safety concern in general public.