1. Institute of Nano- and Biotechnologies (INB); Aachen University of Applied Sciences, Heinrich-Mußmann-Str. 1, 52428 Jülich; Germany
2. Peter Grünberg Institute (PGI-8, Bioelectronics); Research Centre Jülich, 52428 Jülich; Germany
3. Institute of Pharmaceutical Chemistry; Philipps-University Marburg, Marbacher Weg 6-10, 35032 Marburg; Germany