Robust optical trapping of nanoparticles based on flat-band quasi-BICs

Quasi-bound states in the continuum (quasi-BICs) have recently emerged as a compelling platform for nanoscale optical manipulation, due to their pronounced near-field gradients and ultrahigh quality factors (Q-factors). Nevertheless, maintaining trapping performance in the presence of incidence-angle variations and structural perturbations remains a central challenge. Here, we propose a flat-band quasi-BIC based cylindrical dielectric metasurface for trapping nanoparticles. Upon excitation of the flat-band quasi-BIC mode, the resonance remains nearly dispersionless over a wide angular span, thereby establishing a stable optical trapping landscape. Our theoretical analysis further indicates that this platform can reliably confine dielectric nanoparticles with diameters as small as 15 nm, even when structural imperfections are present. These results provide a viable pathway toward angle-tolerant and fabrication-resilient nanoparticle trapping, with potential utility in practical nanophotonic applications.