1. Fraunhofer-Institute of Physical Measurement Techniques IPM, Heidenhofstrasse 8, D-79110 Freiburg, Germany, Gene Scan Europe AG, Engesserstrasse 4B, D-79108 Freiburg, Germany, and Institute for Microsystem Technology, Georges-Köhler Allee 101-103, D-79110 Freiburg, Germany