Magnetic Clustering Effect during the Association of Biofunctionalized Magnetic Nanoparticles with Biomarkers.

We report herein an investigation into dynamic magnetic clustering that occurs during immunoassays as biofunctionalized magnetic nanoparticles (BMNs) become associated with biotargets. We measure the dynamic effective relaxation time τeff(t) and use scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to investigate the C-reactive protein (CRP) as it associates with the BMN Fe3O4-antiCRP to form the magnetic cluster Fe3O4-antiCRP-CRP. The results indicate that τeff(t) increases with increasing association time. In addition, the ration Δτeff/τ0 as a function of CRP concentration follows a characteristic logistic function, which provides a basis for estimating the quantity of biomolecules with a detection sensitivity close to 0.1 ppm. After the association, SEM and TEM images show that CRP and Fe3O4-antiCRP conjugate to form Fe3O4-antiCRP-CRP clusters hundreds of nanometers in size. The SEM and TEM images provide direct evidence of the formation of magnetic clustering.