1. Biophysical Engineering Group, Max Planck Institute for Medical Research, Jahnstraße 29, D-69120 Heidelberg, Germany
2. Department of Physics and Astronomy, Heidelberg University, D-69120 Heidelberg, Germany
3. Department of Cellular Biophysics, Max Planck Institute for Medical Research, Jahnstraße 29, D-69120 Heidelberg, Germany
4. Optical Microscopy Facility, Max Planck Institute for Medical Research, Jahnstraße 29, D-69120 Heidelberg, Germany