1. Chemical and Optical Sensing Division (1.9), Bundesanstalt für Materialforschung und -prüfung (BAM), Richard-Willstätter-Straße 11, D-12489Berlin, Germany
2. Department of Molecular Biology, Umeå University, S-901 87Umeå, Sweden
3. Department of Chemistry, Umeå University, S-901 87Umeå, Sweden
4. Division of Experimental Cancer Research, Department of Translational Medicine, Clinical Research Centre, Lund University, S-214 28Malmö, Sweden