Development of giant magnetoresistive biosensors and systems for early disease detection

Abstract

Giant magnetoresistance (GMR) biosensors have been used with great success for the detection of a variety of biomarkers. Linear GMR biosensors were first proposed in 1998 and have been used since then. The major scientific contribution of this dissertation is to go beyond the previously published models for the linear GMR biosensor and provide analysis of practical design decisions that occur during sensor fabrication. I highlight the central role played by GMR free layer stray field near the sensor edge and present a numerical calculation to guide future linear GMR biosensor design. In addition, I explain how I proposed and demonstrated a novel, non-linear, domain-wall based GMR biosensor, in an effort to detect single molecules. I also describe my contributions to an effort to understand and build upon a previous experimental result using a large area sensor with multidomain switching. The major technological contribution described in this dissertation is the development of a GMR biosensing system that can potentially contribute to the early detection of ovarian cancer and serve as a platform for detecting a wide variety of other biomarkers. System integration included spintronic and nanomagnetic materials engineering, design of a coil with a ferrite core, electrical engineering, analog and digital signal processing, firmware programming, user interface programming on both a PC and an Android smartphone, communications over both USB and Bluetooth, and mechanical design. Hand-held and bench-top systems of this GMR bionsensor were both developed. Both versions use the same sensors, electrical hardware, firmware, and software, but differ mechanically and in the number of sensors available per assay. The bench-top version was completed first and used to demonstrate high sensitivity multiplex detection of ovarian cancer biomarkers CA-125, HE-4, and IL-6, with limits of detection below 10 pg/mL. The hand-held version was then completed and used with a preliminary biotin-streptavidin demonstration. Further development of the hand-held system involves integrating microfluidics.