1. Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
2. Department of Chemistry, Center for NanoScience (CeNS) and Center for Integrated Protein Science, Munich (CIPSM), Ludwig-Maximilians-Universität München, Butenandtstrasse 5-13, D-81377 München, Germany
3. Department of Physics, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States