Acoustomicrofluidic synthesis of ZIF-8/HRP metal–organic framework composites with enhanced enzymatic activity and stability

Encapsulating enzymes within metal–organic frameworks (MOFs) constitute a promising strategy to circumvent their fragile nature in harsh environments, although deleterious molecular conformational changes and decreased substrate accessibility within the pores of the MOF during enzyme loading can often result in decreased catalytic activity. Herein, we report a rapid (within seconds) and facile one-pot aerosol-based method for simultaneous MOF crystallisation and enzyme encapsulation for the synthesis of ZIF-8/horseradish peroxidase (HRP) biocomposites using a high frequency acoustomicrofluidic nebulisation platform. As a consequence of the enhanced mixing and fast crystallisation afforded by the acoustic coupling into the precursors, the resultant combination of enhanced porosity, missing-linker/metal-node defect creation, pore activation and favourable conformational changes to the enzyme secondary structure allows for more efficient enzyme loading and greater enzyme–substrate interactions, and hence stronger enzyme binding within the MOF structure. Together, these culminate in a biocomposite that possesses four times greater enzymatic activity compared to that for the same material synthesized using conventional bulk-solution techniques, and endows the enzyme with increased protective effect (by approximately three to seven times) against high temperature and organic solvents, even after several exposure cycles. Such a possibility facilitates better potential for the enzyme to be recycled—an important factor given their typically high costs and the difficulty in recovering free enzymes in solution.