1. Viikki Drug Discovery Technology Center, Faculty of Pharmacy, P.O. Box 56, FIN-00014 University of Helsinki, Finland, Microelectronics Centre, Helsinki University of Technology, P.O. Box 3500, FIN-02015 HUT, Finland, Laboratory of Analytical Chemistry, Department of Chemistry, P.O. Box 55, FIN-00014 University of Helsinki, Finland, and Department of Pharmaceutical Chemistry, Faculty of Pharmacy, P.O. Box 56, FIN-00014 University of Helsinki, Finland