Enhanced Raman scattering of TNT on nanoparticle substrates: Ag colloids prepared by reduction with hydroxylamine hydrochloride and sodium citrate

Surface-enhanced Raman scattering (SERS) combines extremely high sensitivity, due to enhanced Raman cross-sections comparable or even better than fluorescence, with the observation of vibrational spectra of adsorbed species, providing one of the most incisive analytical methods for chemical and biochemical detection and analysis. Nanoparticles are of fundamental interest since they possess unique size-dependent properties (optical, electrical, mechanical, chemical, magnetic, etc.), which are quite different from the bulk and the atomic state. Metal colloids have become the most commonly used nanostructures for SERS. Silver colloids have been synthesized by chemical reduction methods, and they have been used for detecting TNT in solution with high sensitivity and molecular specificity. The present study focuses on metallic nanoparticles with in the 50-100 nm particle size. The nanoparticles were characterized using techniques such as UV-VIS spectroscopy, Scanning Electron Microscope, Atomic Force Microscopy and Raman Spectroscopy. Detection of TNT deposited on silver colloids was achieved at a wavelength of 532 nm, with a laser operating at 10 mW power (at head). The spectra were obtained in the 100-3500 cm^-1 range by averaging 3 scans for 10 seconds of integration time. Results indicate an increase in the intensity of the vibrational signals due to SERS in TNT which was still detectable by the enhanced presence of the NO₂ out-of-plane bending modes at 820 and 850 cm^-1 and the NO₂ stretching mode at 1300-1370 cm^-1.