Confocal Differential Dynamic Microscopy

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.


  1. 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]
  2. 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]