Micropatterning bacterial suspensions using aqueous two phase systems.

Using an aqueous two-phase system comprised of dextran and polyethylene glycol, this article describes the stable spatial patterning of sub-microlitre droplets of bacterial suspensions. Microdroplets of different types of bacterial populations are positioned and maintained adjacent to each other without significant dispersion even though the bacteria are in suspension and not surface bound. Small molecules, in contrast, diffuse relatively freely between the two aqueous phases. The usefulness of these capabilities is demonstrated by generating a small array of suspensions containing different Escherichia coli strains engineered to respond fluorescently or luminescently to different chemical stimuli. When a chemical stimulus is presented, this droplet array produces a pattern of bacterial "illumination" that reflects the type of chemical to which the array was exposed.