1. Department of Electrical and Computer Engineering; Advanced Materials and Process Engineering Laboratory; University of British Columbia; Vancouver BC V6T 1Z4 Canada
2. Department of Mechanical Engineering; BioInstrumentation Laboratory; Massachusetts Institute of Technology; Cambridge MA 02139 USA
3. Department of Microbiology and Immunology; University of British Columbia; Vancouver BC V6T 1Z1 Canada
4. Department of Chemical and Biological Engineering; University of British Columbia; Vancouver BC V6T 1Z3 Canada