Polarized light scattering is utilized to measure the optical anisotropy and the aspect ratio for nearly spherical colloidal
gold nanoparticles as well as to observe their rotational dynamics which were detected as fluctuations in the time-trace of
the scattering polarization. A comparison between the measured distributions of maximum anisotropy and aspect ratio
with those distributions calculated based on the TEM images analysis are found to show an excellent agreement
confirming the validity of our approach. Our method has the advantage to be simple, easy to implement, and can yield
access to different projections of the particle due to its rotational diffusion. The range of aspect ratios for the sample
being studied is 1 ~ 1.3 and another results for rods with aspect ratio of 2.4 is discussed. Gold nanoparticles have a good
biocompatibility where the possibility of conjugation to a variety of biomolecules and antibodies make them suitable for
optical imaging and optical probes which can be used for nanoscale orientaional sensing to monitor orientations and
rotations of biomolecules during their functional task.
We optically characterized colloidal gold nanoparticles using polarized light scattering which is utilized to investigate both optical anisotropy and aspect ratio of the particle and to observe particle's rotational dynamics. By monitoring time-trace of the polarized scattering from a particle, we could observe rotational dynamics as fluctuations in the measured anisotropy. With typical particle dimension of 97 nm, the maximum anisotropy was measured experimentally to be 0.1 to 0.5, and with comparison to our analytical model, this range is equivalent to an aspect ratio range of 1 to 1.3, which reveals that the colloidals are predominately spherical as predicted by transmission electron microscope (TEM) images analysis. Our method has the advantage to be simple, easy to implement, and can yield access to different projections of the particle due to its rotation. Polarized light scattering can be an ultrasensitive measure for biosensing applications.
Anisotropic metal nanoparticles strongly change the scattered light polarization compared with isotropic nanoparticles,
and this property can be utilized in a sensitive bimolecular recognition due to the high contrast that could be achieved in
polarization microscopy. We report a study of the shape anisotropy in nearly spherical gold nanoparticles and particle
dimers. It was obvious that each particle has its own scattering polarization dependence which reflects the relative
changes in morphologies. Our experimental results reveal that particles with minimum anisotropy don't change the
scattering light polarization which indicates their homogenous shape. Another particles show polarization dependence
scattering intensity due to pronounced anisotropy. Particle dimers possess shape anisotropy that is characterized by a
different polarizability for each axis in the nanostructure. We resolved the internal inhomogeneity in single particles and
particle dimers using a qualitative analysis which enabled us to determine the polarizabilities of both long and short axes
for each particle and particle pair. A few of single particles show a strong optical anisotropy relative to their shape
anisotropy, and even this observation was not yet clarified, it could be used in a sensitive bimolecular detection.