Controlled mixing in microfluidic systems using bacterial chemotaxis.

We demonstrate the use of Escherichia coli and their chemotactic characteristics to enhance mixing in a microchannel in a controlled and bi-directional manner. The presence of a chemoattractant in one arm of a three-junction microchannel results in an asymmetric increase in the effective diffusion coefficient of extremely high molecular weight TMR-Dextran (MW 2 000 000), which rises linearly with the concentration of attractant from a baseline value of 8-42 microm(2)/s at a concentration of 0.1 M. The response to a repellent is similar, with the opposite bias.