1. Office of Cancer Nanotechnology Research, Center for Strategic Scientific Initiatives, National Cancer Institute, NIH, Bethesda, MD 20892, USA.
2. Nanotechnology Characterization Laboratory, Advanced Technology Program, SAIC-Frederick, Inc., NCI-Frederick, Frederick, MD 21702, USA
3. Consultant to the Office of Cancer Nanotechnology Research, Center for Strategic Scientific Initiatives, National Cancer Institute, NIH, Bethesda, MD 20892, USA