Optical trapping and sensing with plasmonic dipole antennas

In this work, we study how to use a plasmonic dipole antenna as a multifunctional nanodevice for surface-enhanced Raman spectroscopy (SERS), localized surface plasmon resonance (LSPR) –based sensing and optical trapping. An analytical model is implemented to link the local electric field enhancement with the gradient forces, as well as the resonance shift caused by the presence of the analyte which can be a molecule or a nanoparticle. We find that a higher local field enhancement induces stronger trapping forces and a larger resonance wavelength shift. Experiments were also performed using plasmonic dipole antennas. Strong SERS signals were observed from the nanogap of an antenna, trapping of Au nanoparticles as small as 10 nm was achieved with a moderate laser power, and evident resonance shifts of the antenna associated with the trapping events were also observed. These results are consistent with our theoretical result that the giant field enhancement generated by a plasmonic dipole antenna also generates strong gradient forces and a high spectral sensitivity.