Application Of Silver Nanoparticles Coated With Starch In Surface-enhanced Raman Spectroscopy

Raman spectroscopy can achieve structural information of the analytes, Raman spectrum analysis is widely used in the study of molecular structure. Surface Enhanced Raman Spectroscopy(SERS) can not only be applied to the acquisition of the structural information, but also to quantitative analysis. Because of the special optical properties, gold and silver nanoparticles are widely used as SERS substrates, especially the silver nanoparticles, which enhancement effect is 10-100 times stronger than that of gold nanoparticles. The stability of silver nanoparticles obtained by the traditional synthesis methods as SERS substrate is poor and its application is limited. In this thesis, the starch-coated silver nanoparticles was synthesized, which can greatly improve the stability of silver nanoparticles. The improved silver nanoparticles were used to determine melamine in milk and malachite green in water sample by SERS method with satisfied results.The starch-coated silver nanoparticles(AgNPs) were synthesized. The SERS activity of the as-synthesized substrates was evaluated by measuring the SERS signals of several different target analytes. The influence of starch concentration on AgNPs was studied and 1.00%(w/v) of starch was selected. The starch-coated AgNPs displayed a higher stability than the classical AgNPs. The starch-coated AgNPs were used as SERS substrate to determine melamine. Under the optimal conditions, melamine was determined in the range of 2.00–50.0 mg L-1 with correlation coefficients of 0.9992 and the detection limit was 0.600 mg L-1. The recovery of melamine in spiked milk samples was 94–104%. These results show that recoveries of melamine and the reproducibility using starch-coated AgNPs are satisfactory.Starch-coated AgNPs and classical AgNPs were synthesized and used to examine malachite green separately. In order to get proper SERS signals, the influence of four experimental conditions were investigated, including volume of AgNPs, hydrochloric acid and sodium chloride solutions and incubation time. Under the optimum conditions, malachite geen was determined in the range of 0.5-35 μg L-1 and 2.5-40 μg L-1 using starch-coated AgNPs and classical AgNPs as SERS substrate, with correlation coefficients of 0.9979 and 0.9953, and the detection limits were 0.0800 mg L-1 and 0.130 mg L-1, respectively. The method was simple, fast, accurate and low cost, which could offer the method for detection of malachite green in water samples.