| Summary: | Magnetite (Fe3O4) nanoparticles with different reaction temperatures (TR = 40, 60 and 80◦C) for the application
of bio-detection have been successfully synthesized using the co-precipitation method. The average crystallite
sizes of samples increased with the increase of TR and all samples showed high crystallinity with an inverse spinel
cubic structure. The grain size increased with the increase of TR. On the other hand, all samples have polycrystalline
structure and the brightest intensity at Miller’s index (311). From the results of the vibrating sample
magnetometer (VSM) analysis, it was found that there was an increase in magnetic properties such as Hc, Mr and
Ms along with the increase reaction temperature. For example, the saturation magnetization increased with the
increase of TR. Next, the giant magnetoresistance (GMR) biosensor was explored by using an exchange-biased
GMR sensor with the Wheatstone bridge method to detect Fe3O4 with variations of reaction temperature in an
alcohol solution of 50 μg/ml. A DC in-plane magnetic field was used for this measurement. It was found that the
Vout curve is sensitive to the presence of Fe3O4 and the maximum Vout appears at 2.8 Oe by applying an external
field to the sensor of ± 95 Oe. The Vout difference increased with the increase of reaction temperature, which can
be attributed to higher saturation magnetization, causing more difficult fringing of the magnetic field. The
relationship between TR and |ΔV| is |ΔV| = 0.0175x + 0.49, in which |ΔV| linearly increases with the increase of
reaction temperature. This study demonstrates the feasibility of Fe3O4-based detection using a GMR sensor and
Fe3O4 as magnetic labels will be useful for potential bio-detection applications.
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