In the last few years, magnetoresistive transducers, such as giant magnetoresistances, have become potential sensing elements in various biosensors for the detection or identification of biomolecules. In these biosensors, magnetic microsized and nanosized particles have been used as markers of biomolecules.

The concept of combining magnetic particles with the sensitivity of magnetoresistive transducers was developed initially by Baselt et al. from the Naval Research Laboratory in Washington in 1998. Since then, many fundamental and application studies on magnetoresistive biosensor have been conducted.

Spin valve-type biosensors and GMR biosensors are the most common biosensor types used in the detection of magnetic particles; Magnetic tunnel junction (MTJ) sensors and the detection of single magnetic particles are still very new. There are few publications on magnetoresistive biosensors and very little work that has been conducted based on magnetic tunnel junction. For this reason, this biosensor has been developed and tested in a laboratory at the University of Bielefeld. Recently, small size MTJ sensors have been developed for the detection of single small size magnetic particles, and this is the subject of the present PhD thesis.