1. Basic Science Program, SAIC-Frederick, Inc., NCI-Frederick, Frederick, Maryland, United States
2. Center for Cancer Research Nanobiology Program, NCI-Frederick, Frederick, Maryland, United States
3. Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106-9510, United States
4. Biomolecular Science and Engineering Program, University of California, Santa Barbara, California 93106-9510, United States