[en] Multifunctional polymer-derivatized superparamagnetic iron oxide (γ-Fe₂O₃) nanoparticles were prepared for biomagnetic separation of histidine-tagged recombinant proteins building up a faster and efficient method for protein separation by making use of their intrinsic magnetic properties. Using polymer bound γ-Fe₂O₃ nanocrystals, a 6x histidine-tagged recombinant protein (silicatein) with a molecular weight of 24 kDa has been isolated and purified. The supermagnetic iron oxide nanocrystals were characterized by transmission electron microscopy (TEM), high-resolution TEM (HRTEM), SQUID and Moessbauer and the polymer functionalization of the γ-Fe₂O₃ nanocrystals was monitored by UV-vis spectroscopy and light microscopy. Protein immobilization and separation was monitored using immunostaining techniques and gel electrophoresis, respectively