Preparation And Pesticide Detection Performance Of Magnetic Silver Composite Microspheres As SERS Substrate

In the recent years, the indiscriminate use of pesticides poses a serious threat to the ecological environment and human health. Pesticide residues could enter into the water, and then accumulate in human body, which could cause endocrine disorders, reproductive and immune disorders and even cancer. At present, Chinese government pays great attention to the issue of excessive pesticide residues in water. However, traditional methods such as liquid chromatography and mass spectroscopy require tedious process of extraction, concentration, purification and others, although they can realize trace pesticide tests. Surface enhanced Raman scattering(SERS) effect of noble metal nanostructures, with the great advantages of extremely high sensitivity and identification of analysts, has been intensely focused and recognized as a powerful and prospective tool in environmental analysis in the field of organic pollutant analysis. Since the SERS performance was strongly influenced by the surface morphology of the substrate, the design of SERS substrate become the focus of the current research. In this dissertation, for fast and selective detection of thiram, the gel system were tried to synthesize Fe3O4-Ag composite microspheres with surface modified with oleate groups and magnetic cores. Through adjusting the reaction parameters, the dumbbell-like Fe3O4-Ag composite microspheres and Fe3O4@Ag core-shell composite microspheres have been successively synthesized, and then used as SERS substrate to detect thiram molecules in solution. The preliminary results revealed that the dumbbell-like Fe3O4-Ag composite microspheres and Fe3O4@Ag core@shell microspheres capped by oleic chain showed excellent selective detection of thiram when used as a SERS substrate. The main results are as follows:(1) Since the magnetic composite microspheres often aggregated together for magnetic attraction, a novel gel reaction system was designed. In the gel system, the special precursor solution, containing oleic, water, ethanol, and silver ions, was transformed into a bulk gel under heating, which limited the reaction in the interior of gel, including the movement of Fe3O4 microspheres. Since the gel system contains oleic acid molecules, we eventually synthesized dumbbell-like Fe3O4-Ag composite microspheres capped by oleic chain by regulating parameters and experimental gel reaction parameters in the system; Additionally, the finally products showed the selective detection of thiram when used as magnetic separable SERS substrates for the surface-capped oleic chain, its detection limit for thiram reached to 10-7 M.(2) Since the dumbbell-like Fe3O4-Ag composite microspheres lack "hot spots" when used as SERS substrate, silver nanoparticles assembled shell were created to enhance the SERS performance. Silver seeds modified Fe3O4 microspheres were used as template and used the above developed gel reaction system. The final obtained Fe3O4@Ag core@shell microspheres exhibited a better detection performance of thiram when used as SERS substrate, and the detection limit reached to 10-8 M, which may be caused by the abundant “hot spots” in the silver shell.