Resonant optical trapping of Janus nanoparticles in plasmonic nanoaperture

Abstract: Controlled trapping of light absorbing nanoparticles with low-power optical tweezers is crucial for remote manipulation of small objects. This study takes advantage of the synergetic effects of tightly confined local fields of plasmonic nanoaperture, self-induced back-action of nanoparticles, and resonant optical trapping method to demonstrate enhanced manipulation of Janus nanoparticles in metallic nanohole aperture. We theoretically demonstrate that displacement of Au-coated Janus nanoparticles toward plasmonic nanoaperture and proper orientation of the metal coating give rise to enhanced near-field intensity and pronounced optical force. We also explore the effect of resonant optical trapping by employing dual laser system, where an on-resonant green laser excites the metal-coated nanoparticle whereas an off-resonant near-infrared laser plays trapping role. It is found that, at optimum nanoparticle configuration, the resonant optical trapping technique can result in three-fold enhancement of optical force, which is attributed to excitation of surface plasmon resonance in Janus nanoparticles. The findings of this study might pave the way for low power optical manipulation of light-absorbing nanoparticles with possible applications in nanorobotics and drug delivery.