NEAR-INFRARED SURFACE-ENHANCED RAMAN-SCATTERING (NIR SERS) ON COLLOIDAL SILVER AND GOLD

Near-infrared surface-enhanced Raman scattering (NIR SERS) was detecte d with high sensitivity for two model compounds, crystal violet and th e DNA base adenine, adsorbed on silver and gold colloidal particles in aqueous solutions. The NIR SERS spectra were measured with a fiber-op tic probe with the use of a Ti:sapphire laser at 850 nm as the excitat ion source and a charge-coupled device (CCD) as the detection system. In a step to achieve the optimal electromagnetic SERS-enhancement cond itions, silver and gold sols were modified to shift their extinction s pectra more to the NIR region. Surface enhancement factors for both cr ystal violet and adenine were estimated to be on the order of 10(6) an d 10(8) for gold and silver, respectively. A larger enhancement factor was observed for adenine with NIR excitation than with visible excita tion. The benefits of NIR SERS and its potential applications are disc ussed.