1. Department of Physics and Astronomy, Tufts University, Medford, Massachusetts 02155, United States
2. Center for Nanoscopic Physics, Tufts University, Medford, Massachusetts 02155, United States
3. Department of Anatomy, University of Wisconsin, Madison, Wisconsin 53706, United States
4. Department of Biomedical Engineering, University of Wisconsin, Madison, Wisconsin 53706, United States
5. Department of Physics, University of Wisconsin, Madison, Wisconsin 53706, United States