A strategy to prepare robust enzyme@covalent organic framework microcapsules: a new platform for biosensing

Enzyme biosensors, despite their high specificity and sensitivity, are constrained by the inherent fragility of enzymes. Despite being considered ideal for enzyme protection by in-situ covalent organic frameworks (COFs) immobilization, the harsh conditions of COFs synthesis often lead to enzyme inactivation. Herein, a strategy was developed to prepare robust enzyme@COFs microcapsules (enzyme@MC_COFs) by the interfacial assembly of hydrophobic COFs spheres to form stable Pickering emulsions, followed by COFs regrowth to reinforce the microcapsules. Compared with conventional methods, this approach confines the enzymes in a mild environment, achievig an impressive encapsulation efficiency of 85.9 %. Enzymes are protected from inhospitable conditions by the mechanical robustness of microcapsules COFs shell which also features adjustable pores to enhance substrate transport and exhibit size selectivity. The success of strategy was verified by the construction of enzyme@MC_COFs based on various hydrophobic COFs spheres (water contact angle>90°) with different pore sizes and degrees of functionalization, and they can be pre-modified to meet specific application requirements. The strategy is simple yet effective. COFs employed in this strategy only requires a slight degree of hydrophobicity, rather than specific functional groups. In addition, a formula was also proposed to predict and control the size of the enzyme@MC_COFs accurately. A cascade catalytic system based on enzyme@MC_COFs has been emulated for the construction of a colorimetric and electrochemical glucose biosensing platform. This study provides new insight into the construction of enzyme@MC_COFs and their biosensing applications.