Phase transition of metal-organic frameworks for the encapsulation of enzymes

Through encapsulating functional materials, metal-organic framework (MOF) composites show extraordinary potential in various fields due to the excellent synergistic effects between the host and guests. However, many attractive functional species, such as enzymes, could be easily damaged during the synthesis of MOF composites. Herein we report a new strategy, namely pressure-induced-stimulated-aging (PISA), in which crystalline MOFs were pressure-treated to induce partial disorder in MOF structures, followed by a recrystallization process to encapsulate enzymes into MOF crystals. The encapsulated enzymes were trapped in the overlap between MOF particles or on the surface of MOFs. Such reversible phase transition avoided high temperature, high ionic strength, strong acid/base conditions, etc., which was suitable for many types of enzymes. Different enzymes can not only be trapped into ZIF-8, but also into other stable MOFs such as Mg-MOF-74, UiO-66, UiO-66-NH₂, MIL-53(Al) and MIL-53(Fe). After optimizing the experimental conditions, Glucose Oxidase (GOx)/UiO-66-WV exhibited similar activity compared to free enzymes. In addition, GOx/UiO-66-WV and GOx/MIL-53(Fe)-WV composites can retain more than 90% of the enzymatic activity after treatment with protease. This strategy will pave a new way for designing MOF composites and exploring further applications in various areas.