1. Department of Physics, University of Osnabrück, 49076 Osnabrück, Germany
2. Department of Biology/Chemistry, University of Osnabrück, 49076 Osnabrück, Germany
3. College of Life Science, Beijing University of Chemical Technology, 100029 Beijing, China
4. Center of Cellular Nanoanalytics (CellNanOs), University of Osnabrück, 49076 Osnabrück, Germany