Detection of the Concentration of MnFe2O4 Magnetic Microparticles Using Giant Magnetoresistance Sensors

In order to explore the in vitro giant magnetoresistive (GMR) biodetection procedure, exchange-biased GMR sensors with a Wheatstone bridge were adopted to detect a series of concentrations of MnFe
₂
O
₄
magnetic microparticle alcohol solution using a direct current in-plane magnetic field measuring method. It is revealed that the output voltage Vout of the transfer curve in the GMR sensor is sensitive to the magnetic microparticles and the maximum Vout appears at a bias field around 2 Oe. The Vout difference between with and without magnetic particles, |ΔV|, linearly increases with particle concentration x undergoing a relationship of |AV| = 11.84x - 93.30, indicating that the unknown concentration x of MnFe
₂
O
₄
particles can be deduced from the measurement of Vout. A lower detectable concentration limit of 12.5 μg/mL is available in the device at this moment, and it can be further improved by reducing the size of magnetic particles.