1. Department of Bioengineering and Center for Nanotechnology, Box 351721, University of Washington, Seattle, Washington 98195, Department of Electrical Engineering, Box 352500, University of Washington, Seattle, Washington 98195, Microdevice Technologies, Sandia National Laboratories, P.O. Box 5800, MS 0603, Albuquerque, New Mexico 87185, and Biomolecular Materials and Interfaces, Sandia National Laboratories, P.O. Box 5800, MS 1413, Albuquerque, New Mexico 87185