1. Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety; Institute of High Energy Physics; Chinese Academy of Sciences; Beijing 100049 P. R. China
2. College of Materials Science and Opto-Electronic Technology; University of Chinese Academy of Sciences; Beijing 100049 P. R.China
3. Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety; National Center for Nanoscience and Technology of China; Beijing 100190 P. R. China