Notes:
We thank Allon Hochbaum for helpful discussion on toxicity and manuscript advice, Ben Hatton and James Weaver for supplying the peristaltic pump and the flow cell, Ilana Kolodkin-Gal for microbiological advice and materials, and Meredith Duffy for additional assistance. TSW thanks Croucher Foundation Postdoctoral Fellowship for financial support. The work was partially supported by the Wyss Institute for Biologically In- spired Engineering at Harvard University and ONR under the award N00014-11-1-0641.