Surface-plasmon-enhanced optical forces in silver nanoaggregates.

We use extended Mie theory to investigate optical forces induced by and acting on small silver nanoparticle aggregates excited at surface plasmon resonance. It is shown that single molecules can be trapped at junctions between closely spaced nanoparticles, which are simultaneously pulled together by optical forces. These effects could significantly influence surface-enhanced Raman scattering and related spectroscopies under normal experimental conditions and contribute to single-molecule sensitivity.