The giant magnetoresistance (GMR) phenomenon is manifested by a large change of the magnetic material's resistance under the application of an external magnetic field. GMR sensors have been used extensively in magnetic hard-drive technology and have sensitivity sufficient to detect individual magnetic bits with sub-100nm dimensions.

Biomolecular sensing in medical diagnosis is a significant focus of recent research. Applying nano-magnetic device engineering to biosensing technology, we have developed a GMR sensor that is extremely sensitive to external magnetic fields and is capable of detecting individual magnetic biolabels. Some significant progress in the development of a tunneling magnetoresistance (TMR) biosensor was also achieved. Herein, the challenges of sensor design, fabrication, and surface functionalization are detailed. Present work enables the production of a highly specific device for the detection of early stage cancer biomarkers, which is the long-term goal of our research.

Arrays of 300 nm-wide GMR sensors were patterned by electron beam lithography and photolithography on a silicon substrate. GMR multilayers (Co/Cu/Co) were deposited by UHV magnetron sputtering with the base pressure of 1.0 × 10^-8 torr. The sensors were conformally coated with 40 nm alumina thin films to electrically insulate the device and protect it from highly corrosive biological media. The sensing capability was confirmed by immobilizing magnetic particles onto the sensor surface, and taking measurements before and after the introduction of particles.