Lipase immobilisation on magnetic silica nanocomposite particles: effects of the silica structure on properties of the immobilised enzyme

Uniformly sized superparamagnetic single-shell nonporous (S1) and double-shell mesoporous silica nanocomposite particles with similar to 130 nm magnetite cluster cores are synthesised in this study. Mesoporous particles are prepared with two BJH pore sizes (2.44 and 3.76 nm, designated as S2 and S3 particles, respectively). Once the lipase was immobilised on particles, our results showed that the enzyme loading capacities of mesoporous structures, i.e. S2 and S3, are higher than that for nonporous particles (S1). Hydrolytic activity tests reveal that immobilised lipases retain about 90% of the free enzyme's activity. Furthermore, comparing to the free enzyme, the thermal stability of immobilised enzymes is considerably enhanced, regardless of the silica matrix structure. Also, our results indicate that the rate of the enzymatic reaction is not influenced by the type of silica matrix used for lipase immobilisation, but immobilisation results in lower enzymatic reaction rates for the immobilised enzymes compared to the free enzyme. Finally, in examining the reusability, the immobilised lipases retained more than 76% of their initial activities after 5 times' reuse.