Synthesis of highly stable silver nanorods and their application as SERS substrates

We report on the improved stability and yield of silver nanorods with well controlled aspect ratios synthesized using a modified seed mediated approach conducted at room temperature. It is found that the longitudinal surface plasmon resonance of these nanoparticles can be tuned in the spectral range 400-700 nm by varying the concentration of seed particles. The surface enhanced Raman scattering (SERS) activity of these nanorods with varying aspect ratios was tested with four dye molecules viz., crystal violet, malachite green, nile blue chloride and rhodamine-6G, using visible and near-infrared laser excitation sources viz., 514.4 and 784.8 nm, respectively. The mechanism of enhancement for the dye molecules adsorbed on these nanorods was investigated in detail. A maximum enhancement factor in the order of 108 was obtained when factors such as the peak wavelength corresponding to the plasmon of the nanorods, the absorption of dye and the excitation line were in close approximation. The linearity obtained in the calibration curves drawn for intense Raman peaks in the SERS spectra of different dye molecules indicated that these substrates are suitable for applications such as biosensing.