Hierarchical micro- and mesoporous ZIF-8 with core–shell superstructures using colloidal metal sulfates as soft templates for enzyme immobilization

Metal–organic frameworks (MOFs), with large specific surface area and tunable porosity, have gained lots of attention for immobilizing enzymes. However, the intrinsic open channels of most reported MOFs are generally smaller than 2 nm, which significantly prevents the passage of enzymes, and the diffusion efficiency of substrates and products. Here we report a new hierarchical micro-mesoporous zeolitic imidazolate framework-8 (ZIF-8) with core–shell superstructure (HZIF-8) using colloidal hydrated zinc sulfate (ZnSO 4 ·7H 2 O) as a soft template for enzyme immobilization. The ZnSO 4 ·7H 2 O forms an aggregation of colloids due to the self-conglobation effect in methanol, which affords a soft template for the formation of HZIF-8. Cytochrome C (Cyt C) was immobilized in interior of HZIF-8 through entrapment during the formation of HZIF-8. The resultant immobilized Cyt C (Cyt [email protected] ) exhibited 4-fold and 3-fold higher activity than free Cyt C and Cyt C encapsulated in conventional microporous ZIF-8 (Cyt [email protected] ), respectively. Meanwhile, the Km value of Cyt [email protected] significantly decreased due to the presence of mesopores compared with Cyt [email protected] , indicating enhanced substrate affinity. After 7 cycles, Cyt [email protected] still maintained 70% of its initial activity whereas Cyt [email protected] only retained 10% of its initial activity. Moreover, the obtained HZIF-8 showed outstanding performance in co-immobilization of multi-enzyme for the detection of glucose.