Optical Trapping of Quantum Dots Based on Gap-Mode-Excitation of Localized Surface Plasmon

Yasuyuki Tsuboi, Tatsuya Shoji, Noboru Kitamura, Mai Takase, Kei Murakoshi, Yoshihiko Mizumoto and Hajime Ishihara

One of the recent hot topics in the fields of plasmonics and related nanophotonics is optical trapping of nano/microparticles based on surface plasmon. Experimental demonstration of such trapping by gap-mode plasmon has hitherto been limited so far to a few reports in which submicrometer polymer beads were trapped with intense irradiation at MW/cm2, satisfying an energetic condition of U > kT. (U is the potential energy of the trap and kT is an averaged thermal background energy.) We demonstrate plasmon-based optical trapping of a luminescent quantum dot (Q dot, diameter ≥10 nm) with a very weak irradiation (0.5−10 kW/cm2). The most important discovery is that the Q dot trapping was clearly observed through luminescence detection even under an energetic condition of U < kT, on the basis of which we propose a novel concept that is peculiar to plasmon-based trapping at a nanogap.

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