Giant magnetoresistance (GMR) sensors based on Co/Cu multilayers for biomaterial detection applications

In this study, a potential biomaterial detection technology was successfully developed based on giant magnetoresistance (GMR) sensors. The GMR sensors were performed using [Co(1.5 nm)/Cu(x)]
₂₀
multilayer structures (x = 0.8, 0.9 and 1.0 nm) fabricated by DC magnetron sputtering. The X-ray diffraction (XRD) patterns showed that Co/Cu film multilayer has a high degree of crystallinity with a single peak correspond to face-centered cubic (111) structure at 2θ = 44.1°. Co/Cu multilayers exhibit soft magnetic behavior with the saturation magnetization (Ms) of 1416, 1463 and 1489 emu/cc and the coercivity (Hc) of 1.5, 1.6, and 112 Oe for x = 0.8, 0.9 and 1.0 nm, respectively. The magnetoresistance (MR) of Co/Cu was about 4.3%, 6.9% and 14.8% for x = 0.8, 0.9 and 1.0 nm, respectively. Furthermore, we used magnetite (Fe
₃
O
₄
) nanoparticles as a biomolecular label (nanotag) synthesized by coprecipitation method. XRD patterns and transmission electron microscopy (TEM) images showed that Fe
₃
O
₄
had well crystallized and grow in their inverse spinel structure, highly uniform morphology with grain size of about 12 nm. The M-H loop of Fe
₃
O
₄
exhibit soft magnetic behavior with Ms of 77 emu/gram and Hc of 47 Oe. The GMR sensor design was used to detect a biomolecule such as formaldehyda and α-amylase enzyme with concentration 20 ppm captured using nanoparticles magnetite coated with polyethylene glycol (PEG) polymer for surface functionalization. Various applied magnetic field of 0-600 Gauss has been performed using electromagnetic with the various current of 0-4.5 A. Induction which cause a shift in MR ratio shown the best response with t
_Cu
= 0.9nm was about 18.3% and t
_Cu
= 1.0nm was about 4.7% for detection formaldehyda and α-amylase enzyme respectively. Furthermore, we present the linearly output signal and saturation signals in real time measurement from sensors. Based on this result, we can conclude that the combination of Co/Cu film multilayer, magnetite, and PEG polymer are potential in biodetection technology.