Super-Resolution Optical Trapping with Control of Localized Plasmonic Fields

We introduce a novel technique for the quantitative analysis of plasmonic trapping potentials experienced by a nanometer-sized particle. Our experimental results show that these potentials have nanoscale spatial structures that re fl ect the near- fi eld landscape of the metal nanostructure. The trap stiffness of plasmonic trapping can be enhanced by three orders of magnitude compared to conventional far- fi eld trapping. We also demonstrated super-resolution optical trapping by observing double potential wells with 80-nm separation, which was realized by a gold double-nonogap structure. In addition, we analyzed the nanoscale spatial pro fi les of plasmonic fi elds within a nanogap, which exhibit complicated fi ne structures created by the constructive and destructive interferences of dipolar, quadrupolar, and higher-order multipolar plasmonic modes. The nanopro fi le can be drastically changed by controlling the excitation optical system, which is applicable to the dynamic nanomanipulation of single molecules and molecular assemblies.