1. James Franck Institute, The University of Chicago, Chicago, IL 60637, USA.
2. Department of Physics, The University of Chicago, Chicago, IL 60637, USA.
3. Institute for Molecular Engineering, The University of Chicago, Chicago, IL 60637, USA.
4. Institute for Molecular Engineering, Argonne National Laboratory, Lemont, IL 60439, USA.
5. Institute for Biophysical Dynamics, The University of Chicago, Chicago, IL 60637, USA.