1. Department of Chemistry, University of Illinois, Urbana, Illinois 61801, United States
2. Center for Biophysics and Quantitative Biology, University of Illinois, Urbana, Illinois 61801, United States
3. Department of Physics, University of Illinois, Urbana, Illinois 61801, United States
4. Department of Chemical and Biomolecular Engineering, University of Illinois, Urbana, Illinois 61801, United States