1. Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, St Lucia, Queensland 4072, Australia
2. Centre for Advanced Imaging, The University of Queensland, St Lucia, Queensland 4072, Australia
3. CAS Key Laboratory for Biomedical Effects of Nanomaterials and Nanosafety and CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing 100190, P. R. China
4. University of Chinese Academy of Sciences, Beijing 100049, P. R. China