Highly sensitive modified giant magnetometer resistance measurement system for the determination of superparamagnetic nanoparticles in continuous flow with application for the separation of biomarkers

Abstract A highly sensitive magnetic measurement system was successfully developed using a modified commercial giant magnetometer resistance (GMR) sensor. The device was placed in a highly uniform magnetic field that was generated by two Helmholtz coil pairs which emit magnetic fields in perpendicular directions to magnetize the SPMNPs and bias the GMR sensor to a linear operating range. The system was used to quantitatively determine the concentrations of superparamagnetic nanoparticles in continuous flow. The characteristics of the proposed system were investigated using three types of superparamagnetic nanoparticles: CoFe2O4, CoFe2O4@Fe3O4, and Fe3O4 with different average particle sizes and magnetic saturation. Coupled with the lock-in measurements, the limit of detection (LOD) for the Fe3O4 nanoparticles was 15.5 μg/mL. The limits of detection for CoFe2O4 and CoFe2O4@Fe3O4 were 74 μg/mL and 96.5 μg/mL, respectively. The results show that Fe3O4 is suitable for this system for the separation and quantification of biomarkers in diagnostics.