Probing roto-translational diffusion of small anisotropic colloidal particles with a bright-field microscope

TL;DR

This paper introduces Squared-Gradient Differential Dynamic Microscopy (SG-DDM), a novel method enabling the measurement of roto-translational dynamics of small anisotropic colloidal particles using bright-field microscopy, overcoming resolution limitations.

Contribution

The paper presents SG-DDM as a new analytical technique to extract rotational and translational motion of tiny anisotropic particles in microscopy.

Findings

SG-DDM successfully measures roto-translational dynamics.

Method applied to peanut-shaped colloids in aqueous suspension.

Analytical and experimental validation provided.

Abstract

Soft and biological materials are often composed of elementary constituents exhibiting an incessant roto-translational motion at the microscopic scale. Tracking this motion with a bright-field microscope becomes increasingly challenging when the particle size becomes smaller than the microscope resolution, a case which is frequently encountered. Here we demonstrate Squared-Gradient Differential Dynamic Microscopy (SG-DDM) as a tool to successfully use bright-field microscopy to extract the roto-translational dynamics of small anisotropic colloidal particles, whose rotational motion cannot be tracked accurately in direct space. We provide analytical justification and experimental demonstration of the method by successful application to an aqueous suspension of peanut-shaped particles.