1. Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
2. Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States
3. Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, United States
4. Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois 60637, United States
5. Department of Biochemistry and Molecular Biology, and Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States