SERS-active nanoaggregates observed with near-infrared laser excitation

Using wide-field illumination, optically active 'hot' particles can be screened from a heterogeneous colloid using a near-IR excitation source. Atomic force microscopy (AFM) correlated with surface-enhanced Raman scattering (SERS) measurements reveal that the majority of these particles are small nanoparticle aggregates. This finding indicates a strong dependence between particle size and Raman enhancement. Furthermore, these 'hot' nanoaggregates display an intermittent on-off emission behavior similar to 'blinking' SERS exhibited at 488 nm and 514 nm laser excitation. This behavior, not observed in bulk SERS studies, can only be examined at the single particle level because of variations in particle size, shape, and surface defects. Further examination at the single particle level using a near-IR excitation source could led to new insights regarding the fundamental nature of 'hot' particles as well as the SERS mechanism.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.