  Optical manipulation has attracted remarkable interest owing to its versatile
and non-invasive nature. However, conventional optical trapping remains
inefficient for the nanoscopic world. The emergence of plasmonics in recent
years has brought a revolutionary change in overcoming limitations due to
diffraction and the requirements for high trapping laser powers. Among the
near-field optical trapping cavity-based systems, Fano resonant optical
tweezers have a robust trapping capability. In this work, we experimentally
demonstrate sequential trapping of 20 nm particles through the use of
metamaterial plasmonic optical tweezers. We investigate the multiple trapping
via trap stiffness measurements for various trapping positions at low and high
incident laser intensities. Our configuration could be used as a light-driven
nanoscale sorting device under low laser excitation. Our results provide an
alternative approach to trap multiple nanoparticles at distinct hotspots,
enabling new ways to control mass transport on the nanoscale.
