SiO₂ microparticles with carbon nanotube-derived mesopores as an efficient support for enzyme immobilization

Abstract

Novel mesoporous SiO₂ microparticles were synthesized by spray pyrolysis using multiwalled carbon nanotubes (MCNTs) as a template. The synthesized multicompartment structure with uniform pores of 12.0 nm was used to immobilize lipase from Thermomyces lanuginosus. The total surface area of mesoporous SiO2 microparticles prepared from silica colloidal solution was increased by 26-folds compared to that of dense SiO2 particles (494 vs 19.0 m(2) g(-1), respectively). Mesoporous SiO₂ particles showed 236% higher protein loading for lipase, than dense SiO₂ particles. The maximum velocity (V-max) and catalytic efficiencies of immobilized lipase were 3.80 and 5.90 folds higher than that of free enzyme. Contact angle analysis revealed increased hydrophobicity of the mesoporous particles, which is advantageous for lid opening at the active center, and increased activity after immobilization. We next developed a lipase/SiO₂/glassy carbon electrode (GCE) biosensors. Cyclic voltammetric results showed linear responses of the lipase/SiO2/GCE bioelectrode towards tributyrin (50-300 mg dL(-1)) as a surface-limited reaction in Tris-HCl buffer. After 12 repetitive uses, dense SiO₂- and mesoporous SiO2-bound lipase retained 74.2 and 95.4% of its original activities, respectively. Thus, given their desirable characteristics and industrial utility, greatly porous SiO₂ particles may provide an excellent support for enzyme immobilization in biosensor development or biocatalysis in organic media.