  Deterministic optical manipulation of fluorescent nanodiamonds (FNDs) in
fluids has emerged as an experimental challenge in multimodal biological
imaging. Designing and developing nano-optical trapping strategies to serve
this purpose is an important task. In this letter, we show how
chemically-prepared gold nanoparticles and silver nanowires can facilitate
Opto-thermoelectric force to trap individual entities of FNDs using a long
working distance lens, low power-density illumination (532 nm laser, 12
${\mu}W/{\mu}m^2$). Our trapping configuration combines the thermoplasmonic
fields generated by individual plasmonic nanoparticles and the
opto-thermoelectric effect facilitated by the surfactant to realise a
nano-optical trap down to a single FND 120 nm in diameter. We utilise the same
trapping excitation source to capture the spectral signatures of single FNDs
and track their position. By tracking the FND, we observe the differences in
the dynamics of FND around different plasmonic structures. We envisage that our
drop-casting platform can be extrapolated to perform targeted, low-power
trapping, manipulation, and multimodal imaging of FNDs inside biological
systems such as cells.
