▎ 摘　　要

Existing techniques for optical trapping and manipulation of microscopic objects, such as optical tweezers and plasmonic tweezers, are mostly based on visible and near-infrared light sources. As it is in general more difficult to confine light to a specific length scale at a longer wavelength, these optical trapping and manipulation techniques have not been extended to the mid-infrared spectral region or beyond. Here, it is shown that by taking advantage of the fact that many materials have large permittivity dispersions in the mid-infrared region, optical trapping and manipulation using mid-infrared excitation can achieve additional functionalities and benefits compared to the existing techniques in the visible and near-infrared regions. In particular, it is demonstrated that by exploiting the exceedingly high field confinement and large frequency tunability of mid-infrared graphene plasmonics, high-performance and versatile mid-infrared plasmonic tweezers can be realized to selectively trap or repel nanoscale objects of different materials in a dynamically reconfigurable way. This new technique can be utilized for sorting, filtering, and fractionating nanoscale objects in a mixture.