  Deterministic placement and dynamic manipulation of individual plasmonic
nanoparticles with nanoscale precision feature an important step towards active
nanoplasmonic devices with prescribed levels of performance and functionalities
at optical frequencies. In this Letter, we demonstrate a plasmonic walker
couple system, in which two gold nanorod walkers can independently or
simultaneously perform stepwise walking powered by DNA hybridization along the
same DNA origami track. We utilize optical spectroscopy to resolve such dynamic
walking with nanoscale steps well below the optical diffraction limit. We also
show that the number of walkers and the optical response of the system can be
correlated. Our studies exemplify the power of plasmonics, when integrated with
DNA nanotechnology for realization of advanced artificial nanomachinery with
tailored optical functionalities.
