Differential Dynamic Microscopy: Diffusion Measurements Where You Want Them

Differential dynamic microscopy (DDM) is an emerging tool for the measurement of diffusion coefficients of macromolecules, especially in the form of particles or aggregates. It combines the benefits of microscopy-versatile modes of imaging, ability to locate regions of interest in structured systems, conventional light sources that do not require laser training, very small samples, and easy sample preparation-with many of the traditional benefits of dynamic light scattering (DLS). After introducing the method in terms that will be familiar to DLS users, examples are presented in ascending order of complexity. Reflecting the learning process of newcomers to DDM, the progression goes from simple latex spheres in free solution to the exquisite capabilities of DDM to explore specific regions of structured, inhomogeneous samples and work efficiently in challenging situations, such as encapsulated particles or colored solutions of conjugated backbone polymers in aggressive solvents at high temperatures. The very different user experiences provided by DDM and DLS are described and compared to multiple particle tracking (MPT). The Perspective closes with a glimpse into DDM's bright future.