Monday, March 9, 2015

A nanotweezer system for evanescent wave excited surface enhanced Raman spectroscopy (SERS) of single nanoparticles

Lingbo Kong, Changwon Lee, Christopher M. Earhart, Bernardo Cordovez, and James W. Chan

We experimentally demonstrate the integration of near-field optical tweezers with surface enhanced Raman scattering (SERS) spectroscopy by using the optical evanescent wave from a silicon nitride waveguide to trap single shell-isolated metallic nanoparticles (NPs) and simultaneously excite SERS signals of Raman reporter molecules adsorbed on the surface of the trapped metallic NPs. Both evanescent wave excited Stokes and anti-Stokes SERS spectra of waveguide trapped single silver (Ag) NPs were acquired, which were compared to their far-field SERS spectra. We investigated the trapping of bare and shell-isolated metallic NPs and determined that the addition of a shell to the metallic NPs minimized particle-induced laser damage to the waveguide, which allowed for the stable acquisition of the SERS spectra. This work realizes a new nanophotonic approach, which we refer to as near-field light scattering Raman (NLS-Raman), for simultaneous near-field optical trapping and SERS characterization of single metallic NPs.

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