The research in biotechnology boomed during the last decade, e.g. the gross investment per year for biotechnology in Germany increased from 24 million euro in 1994 to 150 million euro in 2004 [20]. This caused the evolvement of many new research fields in biotechnology during the last years.
One major research area in biotechnology is the selective detection of biomolecules. Such biosensors are available using many different detection methods. Most methods use markers which bind specifically to the target molecule and can be detected easily. The most common labels are fluorescent markers [107] which are widely commercially available. Other possible markers are nanoparticles [47], radioactive markers [112,11], electrochemical markers [93] or magnetic markers [53], the latter of which are used in this thesis. Recent developments also use marker free detection methods, such as mass [130] and charge sensitive measurements [10] or measurements of the refractive index [99].
Another new trend is the full integration of all laboratory tasks into a lab-on-a-chip. Several research groups [43,79,129,80] try to incorporate the laboratory preparation and detection methods into a portable hand-held device using microfluidic systems [3] and miniaturized detection methods. The use of magnetic markers and magnetoresistive sensors [114] has several advantages for a portable device. The magnetoresistive sensors directly provide an electric signal that can be evaluated with standard electronics, and they can be produced cheaply with standard microelectronic techniques. The pioneering work in this area was done by the Naval Research Laboratory [6], who introduced the BARC biosensor. While most groups use spinvalves for the detection [37,53], some groups also use GMR/TMR sensors [114] or hall effect sensors [38].
Additionally to the sensor systems, magnetic markers allow the manipulation of the attached biomolecules with external magnetic fields. Although the manipulation with magnetic markers is a fairly new idea, several research groups are already working in this area. The magnetic fields can be generated through coils and poles around the sample [29,50,7] or by conducting lines on the chip [51,42,136,31,87]. A few groups have already shown some interesting combinations of magnetic sensors and manipulation systems [52,82].
This thesis especially focusses on the manipulation of magnetic markers with magnetic fields that are generated by conducting lines on a chip. Using currents through conducting lines to create the outer magnetic field allows an easy integration of the manipulation and detection methods into small hand-held devices. This thesis presents several working structures for the manipulation and positioning of magnetic markers. The maximum applied magnetic force is even high enough to use it for bond-force measurements, which are presented for the streptavidin-biotin and avidin-biotin bonds. But such a system is also exact enough to position single magnetic markers within an area of the size of the magnetic marker. Because this system is highly customizable, it is very interesting for many future applications.