1. Department of Chemistry, Nanoscience Center, University of Jyväskylä, P. O. Box 35, FI-40014 JYU, Finland
2. Department of Biological and Environmental Sciences, Nanoscience Center, University of Jyväskylä, P. O. Box 35, FI-40014 JYU, Finland
3. Department of Physics, Nanoscience Center, University of Jyväskylä, P. O. Box 35, FI-40014 JYU, Finland