This paper presents a novel assay of biomarkers consisting of alpha-fetaprotein (AFP) via the measurements of saturation magnetization and magnetic relaxation. The biofunctionalized magnetic nanoparticles (BMNs) were anti-alpha-fetaprotein (antiAFP) coated onto dextran-coated iron oxide nanoparticles, labeled as Fe3O4-antiAFP, and then conjugated with AFP biotargets. After a complete conjugation of AFP and Fe3O4-antiAFP, the BMNs were dried for magnetic measurements. Magnetic nanoparticle images were obtained from magnetic force microscopy with details regarding the transmission electron microscopy images. Findings show that the saturation magnetization Ms increases with a rise in the associated AFP concentration and the magnetic relaxation time τ also shows a rapid increase when the concentration of AFP is lower than 0.2 ppm. Thus, we demonstrate a sensitive platform for detecting biomarkers by characterizing Ms and τ with a sensitivity limit of 0.03-ppm AFP. The results can be attributed to the interparticle interactions and the Néel motion of magnetic moments in BMNs.
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