1. Department of Electrical Engineering, University of California, Los Angeles, California 90095, USA
2. Yokohama Research Laboratory, Hitachi, Ltd., Kanagawa 244-0817, Japan
3. Advanced Photonics Research Institute, Gwangju Institute of Science and Technology, Gwangju 500-712, South Korea
4. California NanoSystems Institute, University of California, Los Angeles, California 90095, USA
5. Department of Chemistry, University of Tokyo, Tokyo 113-0033, Japan
6. Department of Bioengineering, University of California, Los Angeles, California 90095, USA
7. Department of Surgery, David Geffen School of Medicine, University of California, Los Angeles, California 90095, USA