[1] Univ Duisburg Essen, Tech Chem 1, Essen, Germany
[2] Univ Duisburg Essen, Ctr Nanointegrat Duisburg Essen, Essen, Germany
[3] Karlsruhe Inst Technol, Inst Photon Sci & Synchrotron Radiat, Karlsruhe, Germany
[4] Univ Illinois, Dept Chem, Urbana, IL USA
[5] Univ Lubeck, Inst Biomed Opt, Lubeck, Germany