1. School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA.
2. Howard Hughes Medical Institute, Harvard University, Cambridge, MA 02138, USA.
3. Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA.
4. Graduate Program in Biophysics, Harvard University, Cambridge, MA 02138, USA.
5. Department of Physics, Harvard University, Cambridge, MA 02138, USA.