  In nano-optics, a formidable challenge remains in precise transport of a
single optical nano-object along a programmed and routed path toward a
predefined destination. Molecular motors in living cells that can walk
directionally along microtubules have been the inspiration for realizing
artificial molecular walkers. Here we demonstrate an active plasmonic system,
in which a plasmonic nanorod can execute directional, progressive and reverse
nanoscale walking on two or three-dimensional DNA origami.Such a walker
comprises an anisotropic gold nanorod as its body and discrete DNA strands as
its feet. Specifically, our walker carries optical information and can in situ
optically report its own walking directions and consecutive steps at nanometer
accuracy, through dynamic coupling to a plasmonic stator immobilized along its
walking track. Our concept will enable a variety of smart nanophotonic
platforms for studying dynamic light-matter interaction, which requires
controlled motion at the nanoscale well below the optical diffraction limit.
