1. Tianjin Key Laboratory of Radiation Medicine and Molecular Nuclear MedicineInstitute of Radiation MedicineChinese Academy of Medical Sciences & Peking Union Medical College Tianjin 300192 P. R. China
2. CAS Center for Excellence in NanoscienceCAS Key Laboratory for Biomedical Effects of Nanomaterials and NanosafetyChinese Academy of Sciences and National Center for Nanoscience and Technology of China Beijing 100190 China
3. Tianjin Key Laboratory of Biomaterial ResearchInstitute of Biomedical EngineeringChinese Academy of Medical Science and Peking Union Medical College Tianjin 300192 P. R. China
4. University of Chinese Academy of Sciences Beijing 100049 P. R. China