Perspective: Magnetoresistive sensors for biomedicine

Currently, there is a plethora of sensors (e.g., electrochemical, optical, and piezoelectric) used in life sciences for either analyte detection or diagnostic purposes, but in the last decade, magnetic biosensors have received extended interest as a promising candidate for the development of next-generation, highly sensitive biomedical platforms. This approach is based on magnetic labeling, replacing the otherwise classic fluorescence labeling, combined with magnetic sensors that detect the stray field of the superparamagnetic markers (e.g., magnetic micro-nanoparticles or magnetic nanostructures). Apart from the increased sensitivity, magnetic biosensors exhibit the unique ability of controlling and modulating the superparamagnetic markers by an externally applied magnetic force as well as the capability of compact integration of their electronics on a single chip. The magnetic field sensing mechanism most widely investigated for applications in life sciences is based on the magnetoresistance (MR) effect that was first discovered in 1856 by Lord Kelvin. However, it is the giant magnetoresistance effect, discovered by Grünberg and Fert in 1988, that actually exhibits the greatest potential as a biosensing principle. This perspective will shortly explain the magnetic labeling method and will provide a brief overview of the different MR sensor technologies (giant magnetoresistive, spin valves, and tunnel magnetoresistive) mostly used in biosensing applications as well as a compact assessment of the state of the art. Newly implemented innovations and their broad-ranging implications will be discussed, challenges that need to be addressed will be identified, and new hypotheses will be proposed.