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 (ZnSO4 center dot 7H(2)O) as a soft template for enzyme immobilization. The ZnSO4 center dot 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 C@HZIF-8) exhibited 4-fold and 3-fold higher activity than free Cyt C and Cyt C encapsulated in conventional microporous ZIF-8 (Cyt C@ZIF-8), respectively. Meanwhile, the Km value of Cyt C@HZIF-8 significantly decreased due to the presence of mesopores compared with Cyt C@ZIF-8, indicating enhanced substrate affinity. After 7 cycles, Cyt C@HZIF-8 still maintained 70% of its initial activity whereas Cyt C@ZIF-8 only retained 10% of its initial activity. Moreover, the obtained HZIF-8 showed outstanding performance in co-immobilization of multienzyme for the detection of glucose. (C) 2021 Elsevier Inc. All rights reserved.

Automated summary

This study reports a new hierarchical micro-mesoporous zeolitic imidazolate framework-8 (ZIF-8) with core-shell superstructure (HZIF-8) for enzyme immobilization. The immobilized enzyme in HZIF-8 exhibited higher activity and substrate affinity compared to conventional microporous ZIF-8, showing improved stability and reusability. The obtained HZIF-8 also showed outstanding performance in co-immobilization of multienzyme for glucose detection.