Magnetic Biosensing Technologies and Applications

Abstract

Magnetoresistance (MR) biosensors have been widely employed in the detection of small molecules, proteins, and nucleic acids. The major contribution of this thesis is the development of novel giant magnetoresistance (GMR) biosensing technologies to improve the portability, sensitivity, and flexibility of the detection process through both modeling and experimental studies. The work in this thesis can be divided into two major parts, i.e., the development of novel GMR sensors and the development of novel magnetic nanolabels as the labels for the target analytes. The possibility of employing spintronic structures for neuron stimulation is also explored.The optimization of the GMR sensors are from three different aspects. Firstly, GMR biosensors are successfully integrated with a handheld biosensing system, which is capable of fast, accurate, and onsite disease diagnosis. The detection of influenza A virus in swine nasal swab samples is demonstrated with comparable sensitivity to the enzyme-linked immunosorbent assay (ELISA), which is a lab-based golden standard technology for protein detection. Secondly, flexible GMR sensors with a bending radius lower than 1 mm and similar magnetic properties to their rigid counterparts are fabricated with a two-step thinning process. A lab-on-a-needle detection platform is used for cell detection with a LOD of 200 cells in the testing sample, exhibiting great potential in the onsite biopsy at the tumor site, as well as in drug delivery efficacy monitoring as an implanted device. Thirdly, a large-area GMR biosensing scheme based on the reverse nucleation mechanism is proposed, modeled, and demonstrated, which leads to a sensitivity 20 times higher than traditional GMR biosensors. In addition, magnetic nanowires (MNWs) are employed as the magnetic labels for the first time in the cell detection process. The MNWs can be readily internalized into cells without inducing much cytotoxicity. The distance, angular, and concentration dependence of sensor signal generated by the MNWs are studied. Single-cell detection has been successfully realized in the GMR biosensors when the cells are in direct contact with the sensor surface.