Ramachandram Badugu1, Joseph R Lakowicz1, Chris D Geddes1,2. 1. Center for Fluorescence Spectroscopy, Department of Biochemistry and Molecular Biology, University of Maryland Biotechnology Institute, 725 W. Lombard St., Baltimore, MD, 21201. USA. 2. Institute of Fluorescence, University of Maryland Biotechnology Institute, 725 W. Lombard St., Baltimore, MD, 21201. USA.