1. School of Chemistry and Biochemistry Georgia Institute of Technology Atlanta GA 30332 USA
2. Department of Chemical and Biological Engineering, and Hong Kong Branch of the Southern Marine Science and Engineering Guangdong Laboratory The Hong Kong University of Science and Technology Clear Water Bay, Kowloon Hong Kong P. R. China
3. The Wallace H. Coulter Department of Biomedical Engineering Georgia Institute of Technology and Emory University Atlanta GA 30332 USA
4. Institute for Electronics and Nanotechnology Georgia Institute of Technology Atlanta GA 30332 USA
5. Center for Nanophase Materials Sciences Oak Ridge National Laboratory Oak Ridge TN 37831 USA