Magnetic microgels, a promising candidate for enhanced magnetic adsorbent particles in bioseparation: synthesis, physicochemical characterization, and separation performance.

For specific applications in the field of high gradient magnetic separation of biomaterials, magnetic nanoparticle clusters of controlled size and high magnetic moment in an external magnetic field are of particular interest. We report the synthesis and characterization of magnetic microgels designed for magnetic separation purposes, as well as the separation efficiency of the obtained microgel particles. High magnetization magnetic microgels with superparamagnetic behaviour were obtained in a two-step synthesis procedure by a miniemulsion technique using highly stable ferrofluid on a volatile nonpolar carrier. Spherical clusters of closely packed hydrophobic oleic acid-coated magnetite nanoparticles were coated with cross linked polymer shells of polyacrylic acid, poly-N-isopropylacrylamide, and poly-3-acrylamidopropyl trimethylammonium chloride. The morphology, size distribution, chemical surface composition, and magnetic properties of the magnetic microgels were determined using transmission electron microscopy, X-ray photoelectron spectroscopy, and vibrating sample magnetometry. Magnetically induced phase condensation in aqueous suspensions of magnetic microgels was investigated by optical microscopy and static light scattering. The condensed phase consists of elongated oblong structures oriented in the direction of the external magnetic field and may grow up to several microns in thickness and tens or even hundreds of microns in length. The dependence of phase condensation magnetic supersaturation on the magnetic field intensity was determined. The experiments using high gradient magnetic separation show high values of separation efficiency (99.9-99.97%) for the magnetic microgels.