1. Department of Chemistry National University of Singapore 3 Science Drive 3 117543 Singapore
2. National University of Singapore (Suzhou) Research Institute 377 Lin Quan Street Suzhou Industrial Park Jiang Su 215123 P. R. China
3. Department of Physics National University of Singapore Singapore 2 Science Drive 3 117542 Singapore
4. Jiangsu Key Laboratory for Design and Manufacture of Micro-Nano Biomedical Instruments School of Mechanical Engineering Southeast University Nanjing 211189 China
5. Key Laboratory of Mesoscopic Chemistry of MOE and Jiangsu Provincial Lab for Nanotechnology School of Chemistry and Chemical Engineering Nanjing University Nanjing 210023 P. R. China
6. Joint School of National University of Singapore and Tianjin University International Campus of Tianjin University Binhai New City Fuzhou 350207 P. R. China