Zi Gu1, Huali Zuo2, Aihua Wu2, Zhi Ping Xu2. 1. Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane QLD 4072, Australia. Electronic address: z.gu@uq.edu.au. 2. Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane QLD 4072, Australia.