Enhanced Raman Scattering of 2,4,6-TNT Using Metallic Colloids

Surface-enhanced Raman scattering (SERS) combines extremely high sensitivity, due to enhanced Raman cross sections comparable or even better than fluorescence emission. The observation of vibrational spectra of adsorbed species on nanoparticles, provides 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. Bimetallic nanoparticles are of particular interest since they combine the advantages of the individual monometallic counterparts. Metal colloids have become the most commonly used nanostructures for SERS. The present study focuses on the use of metallic nanoparticles, with a particle size of 35-80 nm for detecting TNT in solution. Gold, silver, and Au/Ag colloids were synthesized by chemical reduction methods, and used for detecting TNT in solution with high sensitivity and molecular specificity. The nanoparticles were characterized with UV-VIS spectroscopy, Scanning and Transmission Electron Microscopies and Raman Spectroscopy. The detection of TNT was conducted via an indirect method that involved the alkaline hydrolysis of TNT in the presence of a strong base. This method offered the advantage of generating reaction products that provided enhanced detection in the SERS experiments. The spectra were obtained in the 100-3500 cm^-1 range. The results revealed an increase in the intensity of the vibrational signals, attributed to the SERS spectra of TNT degradation products. Bands associated with out-of-plane bending modes centered at 820 and 850 cm^-1 and symmetric and asymmetric stretching modes were detected.