Particles Transport and Sorting Based on Light Field Regulation in Tunable Graphene Metasurface

In this Letter, we report a nano-optical conveyor belt containing a couple of graphene nano-ribbon pairs (GNRPs) with graded lengths for the realization of trapping and transport of nanoparticles through manipulating the Fermi energy of graphene. In the mid-infrared waveband, graphene behaves like metals, and even more importantly, it supports tunable surface plasmon resonance (SPR) via manipulating its Fermi energy. The spectral responses of these graded graphene nano-ribbons with individual dimensions are dominated by their geometric parameters and surface conductivity, which is tunable and connected with Fermi energy. Optically trapped nano-particles can be transferred from one GNR to another under a single-wavelength polarized excitation beam by sequentially switching the Fermi energy via electric gating. The feasibility of our design to deliver target nano-particles or biomolecules over a long distance with nanometer accuracy is confirmed by the three-dimensional finite-difference time-domain technique. With the capacity to trap and transfer, our design offers a versatile scheme for conducting mechanical sample manipulation in many on-chip optofluidic applications.