Surface-enhanced Raman scattering and plasmon excitations from isolated and elongated gold nanoaggregates

Surface plasmon resonance (SPR) and subsequent surface-enhanced Raman scattering (SERS) of gold nanoaggregates were investigated with reference to hot-sites availability. Correlated SPR and SERS observation of the same sample shows that the plasmon excitations excited at the interstitials of nanoaggregates are more important rather than resonance conditions. The isolated aggregates mostly show a broadened SPR peak centered at ∼560 nm overlapping absorption band of analytes, whereas the elongated aggregates yield several SPR peaks in the longer wavelength region and provide higher enhancement in SERS. Finite-different time-domain analysis predicts that the localization sites get increased at least double in elongated aggregates.