High-Q quasi-BIC metasurfaces for optical trapping of nanoparticles

Metasurfaces have revolutionized nanophotonics by enabling enhanced light-matter interactions at the subwavelength scale. Dielectric metasurfaces supporting quasi-bound states in the continuum (quasi-BICs) can provide strong localized field enhancement, making them highly suitable for nanotweezers. Conventional nanotweezers based on plasmonic nanostructures suffer from excessive Joule heating, which is detrimental for biological nanoparticles. Additionally, trapping of nanoparticles with diameters exceeding 100 nm is challenging due to the restricted gap size available for trapping. To address these limitations, this work explores two designs of amorphous silicon-based quasi-BIC metasurfaces operating at a near-infrared (NIR) wavelength of 1064 nm with negligible heating effect. The proposed metasurfaces exhibit a high quality factor (Q-factor) and strong localized electric field enhancement at the quasi-BIC resonance. Leveraging this large field enhancement, we demonstrate optical trapping of quantum dots (QDs) with an 80 nm diameter using a low input intensity. Furthermore, we show that these metasurfaces can stably trap smaller nanoparticles or biological nanoparticles, such as extracellular vesicles (EVs), with a modest input intensity. The presence of multiple hotspots within the metasurfaces enables the simultaneous trapping of multiple nanoparticles. With significant field enhancement and the ability to trap multiple nanoparticles, the proposed quasi-BIC metasurfaces open new possibilities for nanotweezers.