Colloquium: Roberto Cerbino

Professor Roberto Cerbino, Faculty of Physics, University of Vienna

Differential Dynamic Microscopy: extracting scattering information from microscopy data

Soft and biological matter systems are characterized by structural and dynamical complexity spanning multiple length and time scales. Traditionally, investigating these systems has required a dichotomy of approaches: real-space imaging (microscopy) to resolve local heterogeneity and reciprocal-space scattering (light, X-ray, neutron) to extract robust, ensemble-averaged statistical information. We present Differential Dynamic Microscopy (DDM) as a method that effectively unites these perspectives, transforming a standard optical microscope into a powerful scattering apparatus.

DDM relies on the Fourier analysis of intensity fluctuations within time sequences of digital images and provides access to the intermediate scattering function of the sample (i.e., the sample dynamics), independent of the imaging mechanism (bright-field, phase-contrast, fluorescence, or confocal). This approach allows for the characterization of dynamics across a wide range of wave vectors q, bridging the gap between single-particle tracking and traditional dynamic light scattering (DLS).

Notably, DDM obviates the need to identify and track individual particles, making it uniquely suited for dense, optically opaque, or low-contrast systems where traditional tracking algorithms fail. We will discuss the application of DDM to a diverse array of soft and biological systems. In colloidal physics, DDM enables the precise characterization of aggregation, gelation, and the viscoelastic properties of complex fluids. In the biological realm, we demonstrate its utility in quantifying the multi-scale dynamics of active matter, ranging from the swimming motility of bacteria and spermatozoa to the collective cytoplasmic fluctuations within eukaryotic cells and tissues.

Finally, we will outline recent extensions of the technique, including the application to anisotropic systems and the sizing of proteins in dilute solutions, establishing DDM as a versatile, high-throughput tool for quantitative soft matter physics and biophysics.