1. National Cancer Institute, Center for Cancer Research, Frederick, Maryland 21701, United States
2. University of Delaware, Department of Chemistry and Biochemistry, Newark, Delaware 19716, United States
3. National Institute of Biomedical Imaging and Bioengineering, Laboratory of Cellular Imaging and Macromolecular Biophysics, Bethesda, Maryland 20892, United States
4. University of Delaware, Department of Materials Science, Newark, Delaware 19716, United States