Fabrication and functionalization of dendritic poly(amidoamine)-immobilized magnetic polymer composite microspheres

The synthesis of functionalized magnetic polymer microspheres was described by a process involving (1) preparation of the monodisperse magnetic seeds according to a two-step procedure including the preparation of bilayer-oleic acid-coated Fe3O4 nanoparticles followed by soap-free emulsion polymerization with methyl methacrylate (MMA) and divinyl benzene (a cross-linking agent, DVB); (2) seeded emulsion polymerization proceeding under the continuous addition of glycidyl methacrylate (GMA) monomers in the presence of the magnetic PMMA seeds; and (3) chemical modification of the PGMA shells with ethylenediamine (EDA) to yield amino groups. As such, the magnetic poly(MMA-DVB-GMA) microspheres were prepared possessing monodispersity, uniform magnetic properties, and abundant surface amino groups. Then, the dendritic poly(amidoamine) (PAMAM) shells were coated on the magnetic particles on the basis of the Michael addition of methyl acrylate and the amidation of the resulting ester with a large excess of EDA, which could achieve generational growth under such uniform stepwise reactions. For improving the luminescence properties of the composite particles, fluorescein isothiocyanate, which is a popular organic dye, was reacted with the terminal -NH2 groups from the dendritic PAMAM shells, resulting in the formation of multifunctional microspheres with excellent photoluminescence, superparamagnetic, and pH-sensitive properties. In this case, it can be expected that an extension of the functionalization of these microspheres is to immobilize other target molecules onto the PAMAM shells to introduce other desired functions for potential chemical and biological applications.