VSM measurement showing the magnetic moment as a function of applied magnetic field. The samples of the iron-oxide MNPs with carboxyl groups were measured in the solvent of DI water. The saturation magnetization is 50 emu/g.
(Color online) Schematic drawings of AFP detection with a sandwich-assay configuration. The MgO-based MTJ sensor surface is bonded with the capturing anti-AFP antibodies, and the carboxylated MNPs are covalently coupled to the detecting anti-AFP antibodies. The target AFP antigens can conjugate with both the capturing and detecting anti-AFP antibodies at different epitopes. The inset TEM image shows the monodisperse biofunctionalized MNPs. The isotropic MNPs possess a diameter of 20 nm.
(Color online) TMR transfer curve of the MTJ sensor. The sensor exhibits a TMR ratio 122% and a sensitivity of 0.95%/Oe under 60-Oe hard-axis biasing field. The inset shows the optical image of the MTJ sensor.
(Color online) Diagram of the MTJ sensor resistance variations ΔR after binding with three different concentrations of target AFP antigens. The maximum resistance deviations appear at approximately 40 Oe, with the maximums of 17, 143, and 271 Ω, respectively.
(Color online) Plot of maximum ΔR vs AFP antigen concentration. The error bars represent the standard deviations for the ΔR between 30 Oe and 50 Oe. The fitting curve (solid line) illustrates that ΔR changes logarithmically with the concentration of target AFP antigens.
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