1. National Physical Laboratory, Hampton Road, Teddington, TW11 0LW, U.K.
2. Randall Centre for Cell and Molecular Biophysics, King’s College London, London, SE1 1UL, U.K.
3. Department of Physics and Astronomy, University College London, London, WC1E 6BT, U.K.
4. London Centre for Nanotechnology, University College London, London, WC1H 0AH, U.K.
5. Department of Veterinary Medicine, University of Cambridge, Cambridge, CB3 0ES, U.K.
6. Department of Computer Science, University College London, London, WC1 6BT, U.K.
7. Living Systems Institute, University of Exeter, Exeter, EX4 4QD, U.K.
8. Department of Physics, King’s College London, Strand Lane, London, WC2R 2LS, U.K.