Assaying biomarkers via real-time measurements of the effective relaxation time of biofunctionalized magnetic nanoparticles associated with biotargets

An assay of biomarkers consisting of alpha-fetoprotein (AFP) is reported. Real-time measurements of the effective relaxation time τeff, when the biofunctionalized magnetic nanoparticles (BMNs) were conjugating with biotargets, were made. The BMNs are antialpha-fetoprotein (antiAFP) coated onto dextran-coated iron oxide nanoparticles labeled as Fe3O4-antiAFP. It was found that the effective relaxation time, τeff, increases as the association of AFP and Fe3O4-antiAFP evolves. We attribute this to the enhanced Brownian motion of BMNs when magnetic clusters are present during the conjugation. We found that saturation magnetization, Ms, increases when the concentration of AFP increases. This is due to the fact that more magnetic clusters are associated in the reagent, and therefore the Ms increases when the concentration of AFP increases. The change of effective relaxation time and saturation magnetization shows a behavior of logistic function, which provides a foundation for assaying an unknown amount of biomolecules. Thus, we demonstrate sensitive platforms for detecting AFP by characterizing τeff. The detection platform is robust and easy to use and shows promise for further use in assaying a broad number of biomarkers.