Developmentof High Sensitivity Magnetic Biosensors for Biomedical Applications

Abstract

As a very important subgroup of biosensors, magnetic biosensor is known to possess major advantages over its competitors due to low cost, rapid detection, low background signal in biological tissue and magnetic sensing system has met the requirements to be a portable point-of-care medical system. Providing a useful supplement or alternative for various applications in areas such as diagnosis and cognation study. Detection and quantification of specific biomolecules become increasingly important since the statistical results provide insightful correlation with specific diseases. In the area of disease diagnosis, disease early detection is critical since exposing diseases at early stage will lead to more effective treatments. Biological analytes are low abundance in number or concentration, as a result, many new methods of biosensing are primarily targeting on high sensitivity. One of the promising candidates uses a physical phenomenon called “giant magnetoresistance” (GMR). In GMR element, the electrical resistance changes in response to an applied magnetic field. This technology has been developed and utilized in the hard disk drive industry for decades. Unlike the mature design of GMR biosensor, this dissertation presents a novel GMR magnetic biosensing system with unique particle sensing scheme of localized interaction between particles and sensors. This may provide an alternative path to design GMR sensor with higher sensitivity to truly meet the challenge of detecting low abundance biomolecules in disease early detection. Magnetic sensor can be used in more than assay-based disease detection, it can also be used as a magnetic field sensor to detect magnetic field generated by neuronal electrical activities. Magnetic field generated from neuronal electrical signal is small and it degrades over distance. Great challenge is made for the sensing system to be very sensitive in response to magnetic field, in the same time, to maintain very low overall system noise. We built a Tunnel magnetoresistance (TMR) based magnetic sensing system to address these challenges. TMR stacks and sensor design are optimized to achieve high “zero” field sensitivity, soft magnetic material is sputtered and ion milled to build an integrated magnetic flux concentrator. Sputtering condition and the geometric dimensions of the flux concentrator is also optimized. Low noise analog circuit and different noise reduction methods are utilized to minimize the overall system noise. At last, we have preliminarily demonstrated using our magnetic sensing system to detect brain signals from a rat, Electroencephalography (EEG) sensor is used to verify our magnetic sensor.