Towards optical trapping and enantioselectivity of single biomolecules by interference of collective plasmons

From the point of view of classical electrodynamics, nano-optical and enantioselective tweezers for single biomolecules have been routinely investigated using achiral and chiral localized surface plasmons, respectively. In this work, we propose the use of interference of collective plasmons (Fano-type plasmon) that exist in densely hexagonal plasmonic oligomers to design a high-efficiency nano-optical tweezer to trap individual biomolecules with a radius of 2 nm. For this purpose, we fabricated and simulated 2D hexagonal arrays of Au nanoparticles (AuNPs) with sub-wavelength lattice spacing which support collective plasmons by near-field coupling. Our full-field simulations show that densely hexagonal plasmonic oligomers can enhance the Fano-like resonances arising from the interference of superradiant and subradiant modes. This interference of collective plasmons results in a strong intensification and localization of the electric near-field in the interstice of the AuNPs. The methodology can also be extended to collective chiral near-fields for all-optical enantioseparation of chiral biomolecules with a small chirality parameter (±0.001) with the hypothesis of the existence of strong magnetic near-fields.