1. Department of Chemistry, University of Helsinki, P.O. Box 55, FI-00014 Helsinki, Finland
2. Department of Chemistry, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario K1S 5B6, Canada
3. Department of Food and Nutrition, University of Helsinki, P.O. Box 66, FI-00014 Helsinki, Finland
4. VTT Technical Research Centre of Finland Ltd., P.O. Box 1100, FI-90590 Oulu, Finland
5. Department of Electronics and Nanoengineering, Aalto University, P.O. Box 13500, FI-00076 Espoo, Finland
6. Department of Physics, University of Helsinki, P.O. Box 43, FI-00014 Helsinki, Finland