1. Laboratory
of Molecular Imaging and Nanomedicine, National Institute of Biomedical
Imaging and Bioengineering, National Institutes of Health, Bethesda, Maryland 20892, United States
2. Department
of Chemistry, University of Utah, 315 South 1400 East, Room 2020, Salt Lake City, Utah 84112, United States
3. MOE
Key Laboratory of Macromolecular Synthesis and Functionalization,
Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310027, P. R. China
4. State Key Laboratory of Chemical Engineering, Center for Chemistry of High-Performance & Novel Materials, Department of Chemistry, Zhejiang University, Hangzhou 310027, P. R. China