1. School of Materials Science and Engineering, Nanyang Technological University; 50 Nanyang Avenue Singapore 639798 Singapore
2. School of Pharmaceutical Sciences, Xiamen University; Xiamen Fujian, P. R. China 361102 China
3. School of Biological Sciences; Nanyang Technological University; 60 Nanyang Drive Singapore 637551 Singapore
4. Institute of Molecular and Cell Biology (IMCB); A*STAR, 61 Biopolis Drive, Proteos Building Singapore 138673 Singapore
5. Institute of Chemistry Chinese Academy of Sciences; 2 Zhongguancun North First Street Beijing P. R. China 100190 China