1. Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore
2. Division of Chemistry and Biological Chemistry, School of Chemistry, Chemical Engineering and Biotechnology, Nanyang Technological University, Singapore 637371, Republic of Singapore
3. Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Republic of Singapore
4. Department of Biomedical Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117543, Republic of Singapore
5. Electronic Engineering Department, The Chinese University of Hong Kong, Hong Kong 999077, P. R. China