  Micro- and nanoscale objects with anisotropic shape are key components of a
variety of biological systems and inert complex materials, and represent
fundamental building blocks of novel self-assembly strategies. The time scale
of their thermal motion is set by their translational and rotational diffusion
coefficients, whose measurement may become difficult for relatively large
particles with small optical contrast. Here we show that Dark Field
Differential Dynamic Microscopy is the ideal tool for probing the
roto-translational Brownian motion of shape anisotropic particles. We
demonstrate our approach by successful application to aqueous dispersions of
non-motile bacteria and of colloidal aggregates of spherical particles.

Soft Condensed Matter