* Corresponding authors

^a Center for Hybrid Nanostructures, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
E-mail: rblick@chyn.uni-hamburg.de
Tel: +49 40 42838 1975

^b Center for Molecular Neurobiology Hamburg, University Medical Center Hamburg-Eppendorf, Falkenried 94, 20251 Hamburg, Germany

^c Department of Biochemistry and Molecular Cell Biology, The Calcium Signaling Group, University Medical Center Hamburg-Eppendorf, Martinistraße 52, 20251 Hamburg, Germany

^d Institute for Solid State Physics, Friedrich-Schiller-University Jena, Helmholtzweg 3-5, 07743 Jena, Germany

^e NanoLund, Lund University, Box 118, 22100 Lund, Sweden

^f Solid State Physics, Lund University, Box 118, 22100 Lund, Sweden

^g Material Science and Engineering, College of Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA