Enabling Self-Induced Back-Action Trapping of Gold Nanoparticles in Metamaterial Plasmonic Tweezers

The pursuit for efficient nanoparticle trapping withlow powershas led to optical tweezers technology moving from the conventionalfree-space configuration to advanced plasmonic systems. However, trappingnanoparticles smaller than 10 nm still remains a challenge even forplasmonic tweezers. Proper nanocavity design and excitation has givenrise to the self-induced back-action (SIBA) effect offering enhancedtrap stiffness with decreased laser power. In this work, we investigatethe SIBA effect in metamaterial tweezers and its synergy with theexhibited Fano resonance. We demonstrate stable trapping of 20 nmgold particles with trap stiffnesses as high as 4.18 +/- 0.2 (fN/nm)/(mW/mu m(2)) and very low excitation intensity. Simulations reveal theexistence of two different groups of hotspots on the plasmonic array.The two hotspots exhibit tunable trap stiffnesses, a unique featurethat can allow for sorting of particles and biological molecules basedon their characteristics.