Immobilization of cholesterol oxidase on magnetic fluorescent core-shell-structured nanoparticles.

The magnetic fluorescent core-shell structured nanoparticles, Fe3O4@SiO2(F)@meso-SiO2 nanoparticles, were prepared. Cholesterol oxidase (COD) was immobilized on their surface to form Fe3O4@SiO2(F)@meso-SiO2@COD nanoparticles. Optimal immobilization was achieved with 2.5% (v/v) APTES, 2.0% (v/v) GA, 10mg COD (in 15 mg carrier) and solution pH of 7.0. Fe3O4@SiO2(F)@meso-SiO2@COD nanoparticles showed maximal catalytic activity at pH7.0 and 50°C. The thermal, storage and operational stabilities of COD were improved greatly after its immobilization. After the incubation at 50°C for 5h, the nanoparticles and free COD retained 80% and 46% of its initial activity, respectively. After kept at 4°C for 30 days, the nanoparticles and free COD maintained 86% and 65% of initial activity, respectively. The nanoparticles retained 71% of its initial activity after 7 consecutive operations. Since Fe3O4@SiO2(F)@meso-SiO2@COD nanoparticles contained tris(2,2-bipyridyl)dichloro-ruthenium(II) hexahydrate (Ru(bpy)3Cl2) and were optical sensitive to oxygen in solution, it might be used as the sensing material and has the application potential in multi parameter fiber optic biosensor based on enzyme catalysis and oxygen consumption.