1. Institute of Analytical Chemistry, University of Vienna, Währingerstrasse 38, A-1090 Vienna, Austria, Department of Bioengineering, Compiègne University of Technology, UMR CNRS 6022, BP 20529, 60205 Compiègne Cedex, France, and Swiss Federal Institute of Technology, Biotechnology, ETH Hönggerberg HPT E 77, CH-8093 Zürich, Switzerland