1. Pritzker School of Molecular Engineering, The University of Chicago, Chicago, IL 60637
2. Department of Physics, The University of Chicago, Chicago, IL 60637
3. Department of Electrical and Computer Engineering, Princeton University, Princeton, NJ 08544
4. Department of Chemistry, The University of Chicago, Chicago, IL 60637
5. Center of MicroNanoTechnology, École Polytechnique Fédérale de Lausanne, Lausanne CH-1015, Switzerland
6. Institute of Microengineering, École Polytechnique Fédérale de Lausanne, Lausanne, CH-1015, Switzerland