[1] Univ Washington, Dept Microbiol, Seattle, WA 98105 USA
[2] Univ Washington, Dept Bioengn, Seattle, WA 98105 USA
[3] Univ Washington, Dept Pharmacol, Seattle, WA 98105 USA
[4] Univ Washington, Nanotechnol Ctr, Seattle, WA 98105 USA
[5] ETH, Swiss Fed Inst Technol, Dept Mat, Lab Biol Oriented Mat, CH-8093 Zurich, Switzerland