8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

Tue 611:23-14:00P10.15Enhanced diffusion in a 3D swimmer bath usingdifferential dynamic microscopyAlys Jepson, 1 Vincent Martinez, 1 Chantal Valeriani, 1 Jana Schwarz-Linek, 1 RutBesseling, 1 Alexander Morozov, 1 and Wilson Poon 11 University of Edinburgh, JCMB, The King’s Buildings, Mayfield Road EH9 3JZ, Edinburgh,United KingdomWe have recently developed a novel microscope-based method for the fast, high-throughputcharacterization of the dynamics and motility of active particles based on Differential DynamicMicroscopy (DDM) [1]. Rather than tracking individual trajectories, we measure the timeevolutionof the intensity fluctuations and calculate the Intermediate Scattering Function (ISF),already familiar from dynamic light scattering. Under an appropriate model for the ISF, we extractthe speed distribution, fraction of motile cells and diffusivity in 3D of a population of swimmingbacteria. By averaging over ∼ 10 4 cells, our method is highly accurate compared to conventionaltracking, yielding a routine tool for motility characterisation. We applied the above method tosolutions of active particle (swimming E. coli bacteria) and passive particles (non-swimming E.coli bacteria or colloids). Specifically, we measured the diffusivity of the passive particles inthe 3D active bath, in the bulk of the sample (away from the wall), as function of active particleconcentration. We found an increase in the diffusivity even at low concentration. Preliminaryresults suggest that the diffusion of colloids is enhanced to a significantly lower degree than thediffusion of non-motile (but flagellated) bacteria.[1] Wilson L. G., Martinez V. A., Schwarz-Linek J., Tailleur J., Bryant G., Pusey P. N. andPoon W. C. K., Phys. Rev. Lett. 106, 018101, 2011.15