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 T_eff(f) 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 T_eff(f) increases with increasing association time. In addition, the ration ΔT_eff/T₀as a function of CRP concentration follows a characteristic logistic function, which provides a basis for estimating the quantity of biomole-cules 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.