1. Department of Chemical Engineering, University College London, Torrington Place, London, WC1E 7JE, UK
2. Department of Electronic and Electrical Engineering, University College London, Torrington Place, London, WC1E 7JE, UK
3. UCL Healthcare Biomagnetics Laboratory, University College London, 21 Albemarle Street, London W1S 4BS, UK
4. UCL Nanomaterials Laboratory, University College London, 21 Albemarle Street, London W1S 4BS, UK
5. Biophysics Group, Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, UK
6. The Queen's College, University of Oxford, Oxford OX1 4AW, UK