1. Department of Chemistry and Center for NanoScience, Ludwig-Maximilians-Universität München, 81377 München, Germany
2. Department of Physics and Beckman Institute for Advanced Science and Technology, University of Illinois, Urbana, Illinois 61820, United States
3. Max Planck Institute of Biochemistry, 82152 Planegg, Germany
4. Center of Medical Biotechnology (ZMB) and Center for Nano Integration Duisburg-Essen (CENIDE), University of Duisburg—Essen, 45117 Essen, Germany
5. Cavendish Laboratory, Department of Physics, University of Cambridge, JJ Thomson Avenue, Cambridge, CB3 0HE, United Kingdom