  Plasmonic nanoparticles influence the absorption and emission processes of
nearby emitters due to local enhancements of the illuminating radiation and the
photonic density of states. Here, we use the plasmon resonance of metal
nanoparticles in order to enhance the stimulated depletion of excited molecules
for super-resolved microscopy. We demonstrate stimulated emission depletion
(STED) microscopy with gold nanorods with a long axis of only 26 nm and a width
of 8 nm that provide an enhancement of the resolution compared to
fluorescent-only probes without plasmonic components irradiated with the same
depletion power. These novel nanoparticle-assisted STED probes represent a
~2x10^3 reduction in probe volume compared to previously used nanoparticles and
we demonstrate their application to the first plasmon-assisted STED cellular
imaging. We also discuss their current limitations.
