Magnetic Nanoparticle Images and Assaying Biomarkers via the Magnetic Relaxation of Biofunctionalized Nanoparticles Associated With Biotargets

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 $M_{s}$ increases with a rise in the associated AFP concentration and the magnetic relaxation time $\tau $ 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 $M_{\mathrm {s}}$ and $\tau $ with a sensitivity limit of 0.03-ppm AFP. The results can be attributed to the interparticle interactions and the Neel motion of magnetic moments in BMNs.