Characterization of magnetic relaxation when biofunctionalized magnetic nano-particles are associated with biomarkers in the liquid state in biomedical applications

摘要

This study determined the characteristics of the time-dependent effective relaxation time tau(eff) and magnetization M when biofunctionalized magnetic nanoparticles (BMNPs) associated with biomarkers in a liquid immunoassay. Carcinoembryonic antigen (CEA) was used as the biomarker. BMNP is an anti-CEA that was coated onto dextran-coated Fe3O4 and labeled as Fe3O4-anti-CEA. The phase lag theta of M with respect to the applied field H was measured using a sensitive homemade alternative-current susceptometer, and theta was measured using lock-in detection. The results were used to estimate tau(eff) using the relationship tan theta(t) = omega tau(eff) (t), where 2 pi f = omega and f is the excitation frequency. Delta tau(eff) increased with Phi(CEA), where Delta tau(eff) was the increment of tau(eff) after Fe3O4-anti-CEA associated with CEA, and Phi(CEA) was the concentration of CEA. Additionally, M enhanced when Phi(CEA) increased. We attributed these enhancements to magnetic dipole-dipole interactions among MNPs that contributed extra M and in turn enhanced tau(eff). Magnetic clusters after the association were verified using a transmission electron microscope. This study established the relationship between Delta tau(eff)/tau(eff, 0) and Phi(CEA), where tau(eff, 0) = tau(eff) (Phi(CEA) = 0), allowing the assay of an unknown amount of CEA molecules.