1. Institute of Physics, University of Augsburg, 86159 Augsburg, Germany
2. Center for NanoScience (CeNS), Ludwig-Maximilians-Universität, Munich 80799, Germany
3. Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Box 280, 171 77 Stockholm, Sweden
4. Institute of Theoretical Medicine, University of Augsburg, 86159 Augsburg, Germany