Statistics on Surface-Enhanced Resonance Raman Scattering from Single Nanoshells

Abstract

Silver nanoshells on polystyrene microspheres were used as substrates for surface-enhanced resonance Raman scattering (SERRS). SERRS mapping was recorded from isolated nanoshells coated with Nile blue (NB) and immobilized on gold films and silicon surfaces. Variations in the position and the shape of the ∼590 cm–1 SERRS band of NB within a single nanoshell were observed, as well as fluctuations in integrated SERRS intensities between different isolated nanoshells. The frequency variations were assigned either to different adsorption sites or to different molecular adsorption geometries within a single nanoshell. The intensity fluctuations were rationalized by considering distinct distributions of electromagnetic hotspots in different nanoshells. The SERRS intensity distribution statistics presents a skewed shape with a long tail, which is similar to the characteristic Pareto distribution observed in "single-molecule" surface-enhanced Raman scattering (SERS). The data indicate that a small number of nanoshells yield integrated SERRS intensities an order of magnitude larger than the average, due to the presence of highly efficient hotspots. The statistics of nanoshell SERS presented here points to the need for rigorous analysis of inherent signal variability when such substrates are applied for single-particle chemical sensing and SERS imaging.