1. Biophysics Group, Department of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT, U.K.
2. UCL Healthcare Biomagnetic and Nanomaterials Laboratories, Royal Institution of Great Britain, 21 Albermarle Street, London W1S 4BS, U.K.
3. Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research), 2 Fusionopolis Way, Innovis, #8-03, Singapore 138634, Singapore
4. Department of Chemistry, National University of Singapore, Block S8, Level 3, 3 Science Drive 3, Singapore 117543, Singapore
5. School of Engineering and Science, University of the Sunshine Coast, 90 Sippy Downs Drive, Sippy Downs Queensland 4556, Australia