Near-infrared surface-enhanced Raman scattering of trinitrotoluene on colloidal gold and silver

We report surface-enhanced Raman scattering (SERS) from trinitrotoluene (TNT) adsorbed on colloidal silver and gold in aqueous solutions. Spectra were measured with a fiber optic probe using a diode laser at 830 nm as the excitation source and a charge-coupled device (CCD) as the detection system. Different types of surface-enhanced Raman spectra and enhancement factors have been observed on these metals, indicating differences in adsorption of TNT on gold and silver. Spectra were measured down to 10−7 M TNT in colloidal gold solution, corresponding to a sensitivity of less than 1 pg TNT. Our results demonstrate the potential of SERS for probing TNT with high sensitivity and specificity, and suggest SERS on colloidal gold as a powerful method for detection of TNT and similar species at ultratrace levels.