The immobilization of biomolecules on magnetic nanoparticles is an issue with high potential in different fields. We describe herein a new strategy to immobilize biomolecules on super-paramagnetic nanoparticles based on the reactivity of vinyl sulfone groups with naturally occurring functional groups present in biomolecules (amine and thiol). A new monomer containing a polymerizable methacryloyl group and a secondary amine group was synthesized and used to prepare super-paramagnetic hybrid nanoparticles (SP-HNPs) by two-step miniemulsion polymerization. The Michael addition reaction of divinyl sulfone (DVS) to the secondary amine groups localized on the nanoparticles surface allows the introduction of the vinyl sulfone function in the SP-HNPs (SP-HNPs-VS). The morphology of the functionalized SP-HNPs was characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), dynamic light scattering, and magnetic susceptibility. The capacity of SP-HNPs-VS for the immobilization of biomolecules was evaluated with three model proteins: avidin, invertase, and horseradish peroxidase (HRP). The model proteins were successfully immobilized in mild aqueous conditions compatible with the biological nature of the enzymes. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012