Bacterial locomotion in a wall bounded shear flow

Statistically robust experimental observations on swimming characteristics of bacteria in a wall bounded shear flow are crucial for understanding cell attachment and detachment, interfacial rheology during the initial formation of a biofilm. We combined microfluidics and holography to measure 3-D trajectories of \textit{E. coli} (AW405), subjecting to a carefully controlled shear flow. Experiments are conducted in a straight micro-channel of 40x3x0.2 mm, latter being the depth, with the maximum shear rates up to 200 s$^{-1}$. Holographic microscopic movies recorded at 40X magnification and 15 fps are streamed in real time to a data acquisition computer for an extended period of time ($>$20 min) that allows us to examine long term shear responses. Three-dimensional locations and orientations of bacterial are extracted with a resolution of 0.185 $\mu $m in lateral directions and 0.5 $\mu $m in the wall normal direction. The 3-D trajectories are tracked by an in-house developed particle tracking algorithm. Over thousand 3-D trajectories over a sample volume of 380$\times $380$\times $200 $\mu $m have been obtained. On-going analysis focuses on the effects of flow on cell migration and attachment near a sheared surface.