  Single-molecule surface enhanced Raman scattering (SM-SERS) is one of the
vital applications of plasmonic nanoparticles. The SM-SERS sensitivity
critically depends on plasmonic hot-spots created at the vicinity of such
nanoparticles. In conventional fluid-phase SM-SERS experiments, plasmonic
hot-spots are facilitated by chemical aggregation of nanoparticles. Such
aggregation is usually irreversible, and hence, nanoparticles cannot be
re-dispersed in the fluid for further use. Here, we show how to combine SM-SERS
with plasmon-polariton assisted, reversible assembly of plasmonic nanoparticles
at an unstructured metal-fluid interface. One of the unique features of our
method is that we use a single evanescent-wave optical excitation for
nanoparticle-assembly, manipulation and SM-SERS measurements. Furthermore, by
utilizing dual excitation of plasmons at metal-fluid interface, we create
interacting assemblies of metal nanoparticles, which may be further harnessed
in dynamic lithography of dispersed nanostructures. Our work will have
implications in realizing optically addressable, plasmofluidic, single-molecule
detection platforms.
