1. Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA 02115, USA.
2. Department of Physics and Center for NanoScience, Ludwig Maximilian University, 80539 Munich, Germany.
3. Max Planck Institute of Biochemistry, 82152 Martinsried near Munich, Germany.
4. Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
5. Department of Systems Biology, Harvard Medical School, Boston, MA 02115, USA.