Many efforts in the study of active matter have been dedicated towards the possibility of obtaining directed transport [1]. The bacteria Escherichia coli can be genetically engineered to swim with a light controllable speed [2], which makes them an excellent tool to investigate the physics of active systems. We demonstrate a method to guide these photokinetic bacteria towards any desired region of space. We implement a feedback loop in which the projected light pattern is obtained through geometric transformations of a cell density image captured at an earlier time. With these dynamic light patterns, we are able to only boost bacteria that move in a chosen direction with no need of tracking. This results in a net flow of cells with an associated velocity field that can be controlled in amplitude and direction as predicted by an analytic run and tumble model. Differently from other methods that gather bacteria in areas where their speed decreases [3,4], our method collects the most motile cells in high density and high activity regions that are stable over long time periods. Precisely guiding large populations of bacteria can present relevant applications in microfluidic devices, as well as it is highly interesting for the fundamental study of active matter systems and their statistical mechanic properties.
[1] C. O. Reichhardt and C. Reichhardt, Annu. Rev. Condens. Matter Phys., 8, 51–75 (2017)
[2] J. M. Walter, D. Greenfield, C. Bustamante and J. Liphardt, Proc. Natl. Acad. Sci. U. S. A., 104, 2408–2412 (2007)
[3] J. Arlt, V.A. Martinez, A. Dawson, T. Pilizota and W.C. K. Poon, Nat. Commun, 9, 768 (2018)
[4] G. Frangipane et al., Elife, 7, e36608 (2018)