Surface-enhanced Raman spectroscopic analysis of fonofos pesticide adsorbed on silver and gold nanoparticles

Surface-enhanced Raman scattering (SERS) spectra of fonofos, an organophosphorous pesticide (OPP), were recorded using citrate-reduced silver (Ag) and gold (Au) colloidal nanoparticles in the form of dried films. In this study, significant enhancements were achieved with fonofos concentrations down to similar to 10 ppm with the Ag colloids, demonstrating a potential for the technique in the analysis of fonofos residues. Successful formation of the SERS-active metal aggregates was indicated by the presence of a plasmon band at longer wavelengths in the UV-visible spectrum. Transmission electron microscopy (TEM) images revealed distinctively different morphologies of the aggregates formed by the two metals, while the observed SERS spectral features of fonofos were also found to be different for molecules adsorbed on Ag and Au colloidal surfaces. This evidence suggests metal-induced changes in adsorption behavior of the fonofos analyte, leading to the different binding structures onto the different metal surfaces. Comparisons between the most prominent SERS-enhanced bands and the precise mode descriptions predicted through density functional theory (DFT) simulations at the B3LYP/6-311-FG(d,p) level allowed an in-depth orientation analysis of the adsorbed species on metal surfaces. Nevertheless, the ring vibrations were found to possess a major contribution in the observed SERS enhancements for both metal nanoparticles. Copyright (C) 2010 John Wiley & Sons, Ltd.