1. Institute for Bioscience and Biotechnology Research, Rockville, MD 20850, USA
2. Biomolecular Measurement Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
3. Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742, USA
4. Department of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, OH 44106, USA