High-Gradient Magnetic Separation of Nanoparticles With Ferromagnetic Track-Etched Membrane

We proposed track-etched membrane with a ferromagnetic coating, comparable in thickness to pore diameter, as a separating unit for high-gradient magnetic separation of magnetic nanoparticles (MNPs). A high-gradient magnetic field arisen on a membrane surface in pore vicinity can capture particles of the highest magnetic moment. Ferromagnetic track-etched membrane (FTEM) with pore diameter of 3 ~\mu \text{m} has been coated with a layer of Permalloy (Fe 20 Ni 80 ) of 1 and 2~ \mu \text{m} replicating the membrane pore structure. MNPs were separated by their size and magnetic properties on the FTEM. Magnetite hydrosol of an average particle size of 50 nm was fractioned into eluate with an average particle diameter 30-35 nm and retentate with an average particle diameter 65 nm using the FTEM with the 3~\mu \text{m} pores. The advantages of thicker ferromagnetic layers for effective separation of sub-micrometer magnetic particles have been confirmed both theoretically and experimentally.