Multiplexed Near-Field Optical Trapping Exploiting Anapole States

Optical tweezershave had a major impact on bioscienceresearchby enabling the study of biological particles with high accuracy.The focus so far has been on trapping individual particles, rangingfrom the cellular to the molecular level. However, biology is intrinsicallyheterogeneous; therefore, access to variations within the same populationand species is necessary for the rigorous understanding of a biologicalsystem. Optical tweezers have demonstrated the ability of trappingmultiple targets in parallel; however, the multiplexing capabilitybecomes a challenge when moving toward the nanoscale. Here, we experimentallydemonstrate a resonant metasurface that is capable of trapping a highnumber of nanoparticles in parallel, thereby opening up the fieldto large-scale multiplexed optical trapping. The unit cell of themetasurface supports an anapole state that generates a strong fieldenhancement for low-power near-field trapping; importantly, the anapolestate is also more angle-tolerant than comparable resonant modes,which allows its excitation with a focused light beam, necessary forgenerating the required power density and optical forces. We use theanapole state to demonstrate the trapping of 100's of 100 nmpolystyrene beads over a 10 min period, as well as the multiplexedtrapping of lipid vesicles with a moderate intensity of <250 & mu;W/& mu;m(2). This demonstration will enable studies relating to the heterogeneityof biological systems, such as viruses, extracellular vesicles, andother bioparticles at the nanoscale.