|Jörg Schotter1, Hubert Brückl1, Günter Reiss1, P. B. Kamp2, Anke Becker2, and Alfred Pühler2
1Department of Physics and 2Department of Biology, University of Bielefeld, Universitätsstr. 25, D-33615 Bielefeld, Germany
Compared to the established fluorescent labeling method, the use of magnetic markers in biochip sensors has important advantages with respect to the detection of biomolecules at low concentrations [1,2]. The magnetic markers are commercially available superparamagnetic microspheres. We demonstrate the applicability and functionality of both Giant Magnetoresistance (GMR) and Tunnel Magnetoresistance (TMR) sensors for detecting magnetic markers. The GMR-sensors consist of patterned Cu/NiFe multilayers in the second antiferromagnetic maximum, whose resistance vs. field dependencies can be tailored for large sensitivity (up to 3%/Oe). Initial experiments with TMR sensors take advantage of the larger signal amplitude of around 40 % and corresponding sensitivity of 12 %/Oe. The measured signals for the detection of DNA-fragments show that the magnetic biosensors are more sensitive than current fluorescent detection units.