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The translational and rotational diffusion of a series of gold nanorods with low aspect ratio was investigated by dynamic light scattering (DLS). It is shown that the translational and the rotational diffusion coefficient can be determined because the particle shape causes an anisotropy of the polarizability. This gives rise to two clearly distinguishable relaxation modes in the time correlation function of the scattered light. The particle length and aspect ratio were determined independently by transmission electron microscopy (TEM). Using a hydrodynamic model, these geometrical parameters were converted to diffusion constants, which agree well with the values determined by DLS. Additionally it is possible to obtain an estimate of the particles aspect ratio from the amplitude ratio of the two relaxation modes.

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The diffusivity of spherical colloidal particles close to a planar hard wall is studied by dynamic light scattering with evanescent illumination. A novel setup allows us to independently vary the scattering vector components parallel Q parallel and normal Q perpendicular to the wall. An expression for the initial decay rate Gamma of the time autocorrelation functions is derived as a function of both Q parallel and Q perpendicular, as well as the penetration depth of the evanescent wave, where hydrodynamic interactions of particles with the wall are included. This makes it possible to study the viscous wall drag effect quantitatively for particles as small as 85 nm in radius.