1. Department of Pediatrics, Radiology, and Microbiology and Immunology, Stanford University, Clark Center, 318 Campus Drive, Stanford, California 94305, Chemistry and Materials Science Directorate, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94551, and NSF Center for Biophotonics Science and Technology, University of California, Davis, 2700 Stockton Boulevard, Suite 1400, Sacramento, California 95817