1. Department of Chemical and Biomolecular Engineering National University of Singapore 4 Engineering Drive 4 Singapore 117585 Singapore
2. Institute of Materials Research and Engineering A*STAR (Agency for Science, Technology and Research) 2 Fusionopolis Way, Innovis Singapore 138634 Singapore
3. Centre for Advanced 2D Materials Graphene Research Centre National University of Singapore Singapore 117546 Singapore
4. Institute of Molecular Science Shanxi University Taiyuan 034000 P. R. China
5. Key Laboratory for Organic Electronics and Information Displays and Jiangsu Key Laboratory for Biosensors Nanjing University of Posts and Telecommunications Nanjing 210023 P. R. China
6. Laboratory of Luminescence Analysis and Molecular Sensing (Southwest University) Ministry of Education School of Chemistry and Chemical Engineering Southwest University Chongqing 400715 P. R. China
7. Department of Physics National University of Singapore Singapore 117542 Singapore
8. Department of Biomedical Engineering National University of Singapore 4 Engineering Drive 3 Singapore 117583 Singapore
9. Department of Materials Science and Engineering National University of Singapore 9 Engineering Drive 1 Singapore 117575 Singapore