We introduce confocal differential dynamic microscopy (ConDDM), a new technique yielding information comparable to that given by light scattering but in dense, opaque, fluorescent samples of micron-sized objects that cannot be probed easily with other existing techniques. We measure the correct wave vector q-dependent structure and hydrodynamic factors of concentrated hard-sphere-like colloids. We characterize concentrated swimming bacteria, observing ballistic motion in the bulk and a new compressed-exponential scaling of dynamics, and determine the velocity distribution; by contrast, near the coverslip, dynamics scale differently, suggesting that bacterial motion near surfaces fundamentally differs from that of freely swimming organisms.
- Peter J. Lu et al., “Characterizing Concentrated, Multiply Scattering, and Actively Driven Fluorescent Systems with Confocal Differential Dynamic Microscopy” Physical Review Letters. 108, 218103 (2012). [pdf] [Supp. Info]
- Fabio Giavazzi, Paolo Edera, Peter J. Lu, Roberto Cerbino, “Image windowing mitigates edge effects in Differential Dynamic Microscopy” The European Physical Journal E. 40, 97 (2017). [pdf]