1. Center for Fluorescence Spectroscopy, Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, 725 West Lombard Street, Baltimore, Maryland 21201, Departments of Pharmacology and Internal Medicine, University of Virginia Health System, Box 800735, Charlottesville, Virginia 22908, Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439, and Lumerical Solutions Inc., 201−1290 Homer Street, Vancouver, British Columbia, Canada V6B 2Y5