Sub-10 nm particle trapping enabled by a plasmonic dark mode.

We demonstrate that a highly localized plasmonic dark mode with radial symmetry, termed quadrupole-bonded radial breathing mode, can be used for optically trapping the dielectric nanoparticles. In particular, the annular potential well produced by this dark mode shows a sufficiently large depth to stably trap the 5 nm particles under a relatively low optical power. Our results address the quest for precisely trapping sub-10 nm particles with high yield and pave the way for placing sub-10 nm particles conforming to a specific geometric pattern.