Fabrication of a Silica Coating on Magnetic γ-Fe₂O₃ Nanoparticles by an Immobilized Enzyme

Silicatein, a hydrolytic protein encountered in marine sponges, was immobilized on maghemite (γ-Fe 2 O 3 ) nanoparticles that were surface functionalized with a reactive mulfunctional polymer. This polymer carries an anchor group based on dopamine which is capable of binding to the γ-Fe 2 O 3 surface and a reactive functional group which allows binding of various biomolecules onto inorganic nanoparticles. This functional nitrilotriacetic acid (NTA) group allows immobilization of His-tagged silicatein on the surface of the γ-Fe 2 O 3 nanoparticles. The surface-bound protein retains its native hydrolytic activity to catalyze formation of silica through copolymerization of alkoxysilanes Si(OR) 4 . Functionalization of the magnetic nanoparticles and the architecture of the SiO 2 -coated γ-Fe 2 O 3 nanoparticles was confirmed by TEM studies as well as by FT-IR and optical microscopy.