Optical characterization for nearly spherical gold colloidals via their polarization response

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.