1. Research Group Nanotechnology for Life Science, Fraunhofer Institute for Applied Polymer Research, Geiselbergstrasse 69, Potsdam 14476, Germany, Department of Pediatrics, Ludwig-Maximilians University, Lindwurmstrasse 2a, D-80337 Munich, Germany, and Department of Chemistry, Philipps-Universität Marburg, Hans-Meerwein Strasse, D-35032 Marburg, Germany