Microfluidics for the Rapid Detection of Pathogens Using Giant Magnetoresistance Sensors

This paper presents an integrated solution toward an on-chip microfluidic diagnostic system using the magnetically induced motion of functionalized magnetic microparticles (MPs) in combination with giant magnetoresistance (GMR) sensors. The innovative aspect of the proposed method is that the induced velocity on MPs in suspension, while imposed to a magnetic field gradient, is inversely proportional to their volume. Specifically, a velocity variation of suspended functionalized MPs inside a detection microchannel with respect to a reference velocity, specified in a parallel reference microchannel, indicates an increase in their nonmagnetic volume. This volumetric increase of the MPs is caused by the binding of pathogens (e.g., bacteria) to their functionalized surface. The new formed compounds, which have an increased nonmagnetic volume, are called loaded MPs (LMPs). Experiments with functionalized MPs and LMPs with Escherichia coli attached to their surface were conducted as a proof of concept. Their movement was demonstrated optically by means of a microscope with a mounted CCD camera as well as by measuring the resistance change of the integrated GMR sensors.