GMR Biosensor Based on Spin-Valve Thin Films for Green-Synthesized Magnetite (Fe3O4) Nanoparticles Label Detection

The giant magnetoresistance (GMR) thin film with spin valve (SV) structure of Ta (2 nm)/Ir20Mn80(10 nm)/Co90Fe10(3 nm)/Cu (2.2 nm)/Co84Fe10B4(10 nm)/Ta (5 nm)] fabricated by RF magnetron sputtering method with a magnetoresistance (MR) of 6% was used in this work. Green synthesis of Fe3O4 magnetic nanoparticles (MNPs) using Moringa Oleifera (MO) leaf extract have been successfully conducted using the coprecipitation method. Fe3O4 MNPs demonstrated the inverse cubic spinel structure with the average crystallite size of 13.8 nm and decreased to 11.8 nm for Fe3O4/PEG. Fe3O4, as a magnetic label, integrated with a Wheatstone bridge-GMR sensor provides access to GMR-based biosensors. The induced-field increase leads the signal (ΔV) to increase with increasing nanoparticle concentration. It was discovered that a sensor can distinguish different types of magnetic labels. The sensitivity for Fe3O4 and MO-green synthesized Fe3O4 magnetic label was 0.04 and 0.1 mV/g/L, respectively. The GMR sensor performed the highest sensitivity on the MO-green synthesized Fe3O4 label. Thus, the SV thin film as a sensor and the green-synthesized Fe3O4 nanoparticles as a superior magnetic label are an excellent combination for biosensor application.