Nanoparticle Trapping in a Quasi-BIC System

Plasmonic nanotweezers employing metallic nanoantennas provide a powerful tool for trapping nanoscale particles, but the strong heating effect resulting from light absorption limits widespread applications. Here, we propose an all-dielectric nanotweezer harnessing quasi-bound states in the continuum (quasi-BICs) to enable the trapping of nanoscale objects with low laser power and a negligible heating effect. The quasi-BIC system provides very high electromagnetic field intensity enhancement that is an order of magnitude higher than plasmonic systems as well as high-quality-factor resonances comparable to photonic crystal cavities. Furthermore, the quasi-BIC metasurface tweezer array provides multiple optical hotspots with high field confinement and enhancement, thereby generating multiple trapping sites for the high-throughput trapping of nanometer-scale objects. By purposefully truncating the tips of the constituent elliptical nanoantennas in the quasi-BIC system to leverage the asymmetric field distribution, we demonstrate that the optical gradient forces can be further enhanced by a factor of 1.32 in comparison to the intact elliptical nanoantenna, which has attractive potential in subwavelength particle trapping applications. In addition, we show that trapped particles can improve the resonance mode of the cavity rather than suppress it in a symmetry-broken system, which in turn enhances the trapping process. Our study paves the way for applying quasi-BIC systems to low-power particle trapping and sensing applications and provides a new mechanism to harness the self-induced back-action.