Thesis (M.Sc.)--Chulalongkorn University, 2015

Silver nanoparticles (AgNPs) have been widely used as substrates to enhance Raman signals of molecules oriented nearby the AgNPs surface. This improves the detection limit via surface-enhanced scattering (SERS) technique. In this research, the coupling reaction of diazonium ion combined with SERS provides a selective and sensitive detection method for trace analysis of carbofuran, which is one of the most toxic carbamate insecticides. Diazonium ion specifically reacts with carbofuran phenol created from the alkaline hydrolysis of carbofuran to generate azo dye complex. In SERS measurement, the generated azo compound is easily deposited on the surface of AgNPs by strong Ag–S bond; therefore, the strong Raman intensity of the azo dye can be observed. To quantify carbofuran, the ratio of Raman intensity at 1201 cm-1 over 1021 cm-1 were linearly plotted against the concentrations of carbofuran with R2 = 0.9891 in the range of 0.1–5 ppm. The limit of detection (LOD) is 0.729 ppm. Moreover, our proposed carbofuran detection method was insignificantly influenced by interferences e.g., small acid molecules and monosaccharide sugars. For practical analysis, the developed method of carbofuran detection was also studied in real agricultural products (e.g., rice, beans, peppers, sesame).