Encapsulating lipase on the surface of magnetic ZIF-8 nanosphers with mesoporous SiO2 nano-membrane for enhancing catalytic performance

The preparation of immobilized enzyme with excellent performance is one of the difficulties that restrict the application of enzyme catalysis technology. Here, Candida rugosa lipase (CRL) was firstly adsorbed on the surface of magnetic zeolitic imidazolate framework-8 (ZIF-8) nanospheres, which was further encapsulated with a mesoporous SiO2 nano-membrane formed by tetraethyl orthosilicate (TEOS) polycondensation. Consequently, lipase could be firmly immobilized on carrier surface by physical binding rather than chemical binding, which did not damage the active conformation of enzyme. There were mesopores on the silica nano-membrane, which could improve the accessibility of enzyme and its apparent catalytic activity. Moreover, silica membrane encapsulation could also improve the stability of enzyme, suggesting an effective enzyme immobilization strategy. It showed that TEOS amount and the encapsulation time had significant effects on the thickness of silica membrane and the enzyme activity. The analysis in enzyme activity and protein secondary structure showed that lipase encapsulated in silica membrane retained the active conformation to the greatest extent. Compared with the adsorbed lipase, the encapsulated lipase increased its thermostability by 3 times and resistance to chemical denaturants by 7 times. The relative enzyme activity remained around 80% after 8 repetitions, while the adsorbed lipase only remained at 7.3%.