1. Faculty of Science and Engineering, Åbo Akademi University, Henriksgatan 2, Turku FI-20500, Finland
2. Department of Chemistry, Nanoscience Center, University of Jyväskylä, Jyväskylä FI-40014, Finland
3. Institute of Biomedicine, University of Turku, Kiinamyllynkatu 10, Turku FI-20520, Finland
4. Wihuri Physical Laboratory, Department of Physics and Astronomy, University of Turku, Turku FI-20014, Finland