Correlating the Shape, Surface Plasmon Resonance, and Surface-Enhanced Raman Scattering of Gold Nanorods

We report the study correlating the shape, surface plasmon resonance (SPR), and surface-enhanced Raman scattering (SERS) of gold nanorods (NRs) in dilute colloids. A series of gold NRs with various aspect ratios was prepared via an improved seed-mediated technique. Increasing the aspect ratio finely tunes the position of the longitudinal plasmon mode of the NRs in a wide spectral range. This shape-dependent SPR behavior was simulated by Gans theory and the discrete dipole approximation method. The subtle influence of SPR on SERS was then demonstrated by gradually tuning the SPR wavelength across a fixed excitation line. SERS experiments and theoretically predicted electromagnetic enhancement by the three-dimensional finite-difference time domain method clearly demonstrate that overlapping SPR and the excitation line maximizes the SERS enhancement. This correlation thus enables a quick diagnosis of SERS intensity by looking at the position of the SPR band.