1. Center for Biomolecular Recognition, Department of Medical Biochemistry and Genetics, The Panum Institute, Blegdamsvej 3c, DK-2200 Copenhagen N, Denmark, PNA Diagnostics A/S, Rønnegade 2, DK-2100 Copenhagen Ø, Denmark, and Department of Physical Chemistry, Chalmers University of Technology, S-412 96 Gothenburg, Sweden