1. Beijing Engineering Research Center for BioNanotechnology & CAS Key Laboratory for Biological Effects of Nanomaterials and Nanosafety; National Center for NanoScience and Technology; Beijing 100190 P. R. China
2. State Key Laboratory of Nonlinear Mechanics; Institute of Mechanics; Chinese Academy of Sciences; Beijing 100190 P. R. China
3. Department of Mechanical and Automation Engineering; The Chinese University of Hong Kong; Shatin, N.T. Hong Kong SAR China