  We present a novel approach to determine the optical properties of materials
in the nanoscale range using optical tweezers (OT). Fluorescent polymer-based
nanostructures (pdots) are optically trapped in a Gaussian beam OT and the trap
stiffness is studied as a function of various parameters of interest. We
explicitly show that properties such as the refractive index and the optical
anisotropy of these nanostructures can be determined with high accuracy by
comparing the experimental data to an optical force model. In particular, we
demonstrate that the effective optical properties of these pdots can be
modulated by changing the light wavelength that excites the sample, opening the
door for a fine tuning of their optical response, with possible applications in
the development of new sensors and/or other optoelectronic devices.
