Analysis of localized surface plasmon resonance by elastic light-scattering spectroscopy of individual Au nanoparticles for surface-enhanced Raman scattering

The size, shape, and environment dependence of localized surface plasmon resonance (LSPR) from individual Au nanoparticles was investigated using light-scattering microspectroscopy, which is highly-sensitive to the above factors. Here we identified that scattering angle dependence of LSPR bands cannot be completely neglected when the radius of a Ag nanoparticle was larger than 40 nm. This was based on a comparison between calculated Mie-resonance and experimental results of light-scattering spectra. The variations in LSPR bands of Au nanoparticles which were embedded in polymer films were attributed to variations of particle size and shape. Interestingly, we observed twin peaks in the light-scattering spectra of several Au nanoparticles. From correlated polarization light-scattering spectroscopy and scanning electron microscopy analyses, we identified twin peaks that originated from nanoparticle aggregates in which two spheroid particles were touching each other. Also, based on the light-scattering spectroscopy of Au nanoparticles covered with different media, we identified changes of the LSPR bands in different dielectric medium which depended on the nanoparticle shape.