  We present a method to locally probe spatially varying chemical composition
of soft matter systems by use of optically controlled and elastically
self-assembled plasmonic nanoantennae. Disc-shaped metal particles with sharp
irregular edges are optically trapped, manipulated, and assembled into small
clusters to provide a strong enhancement of the Raman scattering signal coming
from the sample regions around and in-between these particles. As the particles
are reassembled and spatially translated by computer-controlled laser tweezers,
we probe chemical composition as a function of spatial coordinates. This allows
us to reliably detect tiny quantities of organic molecules, such as capping
ligands present on various nanoparticles, as well as to probe chemical
composition of the interior of liquid crystal defect cores that can be filled
with, for example, polymer chains. The strong electromagnetic field enhancement
of optically-manipulated nanoparticles rough surfaces is demonstrated in
different forms of spectroscopy and microscopy, including enhanced spontaneous
Raman scattering, coherent anti-Stokes Raman scattering, and stimulated Raman
scattering imaging modes.
