Dark Field Differential Dynamic Microscopy enables the accurate characterization of the roto-translational dynamics of bacteria and colloidal clusters

TL;DR

Dark Field Differential Dynamic Microscopy provides an effective method for accurately measuring the combined translational and rotational Brownian motion of anisotropic particles like bacteria and colloidal clusters, especially when optical contrast is low.

Contribution

This paper introduces Dark Field Differential Dynamic Microscopy as a novel technique for characterizing the roto-translational dynamics of anisotropic particles, overcoming previous limitations in optical contrast.

Findings

Successfully applied to bacteria and colloidal aggregates

Accurately measures roto-translational diffusion coefficients

Effective for particles with low optical contrast

Abstract

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.