Enhanced activity of enzyme encapsulated in hydrophilic metal-organic framework for biosensing

The strategy of enzyme immobilization has been widely employed in biocatalysis and biosensing, but the poor catalytic activity hinders their further application. Herein, a strategy of Glucose Oxidase (GOx) encapsulated in zeolitic imidazolate framework-90 (GOx@ZIF-90) with hydrophilic properties was proposed, which was integrated with Pt nanozyme (GOx@ZIF-90-Pt NPs) to design a cascade catalytic reaction for biosensing. In this study, the activity of GOx in GOx@ZIF-90 was about 90% of the free enzyme activity (defined as 100%), and showed 4.5-folds higher than that of GOx@ZIF-8 (20%), which was attributed to that hydrophilic ZIF-90 frame could regulate interfacial interactions and hold its natural conformation, maintaining the catalytic activity of the packaged enzyme. Meanwhile, the affinity toward substrates of GOx@ZIF-90 improved 2.0-folds compared to GOx@ZIF-8, resulting in the improvement of the catalytic efficiency. Inspired by this, a cascade system (GOx@ZIF-90-Pt NPs) was fabricated by integrating GOx@ZIF-90 with Pt nanozyme, which was employed for glucose sensing and Bisphenol A (BPA) detection in immunoassay. Combined with smartphone platform, a hydrogel sensor based on GOx@ZIF-90-Pt NPs was developed for visual and quantitative measurement of glucose. Overall, this study provided an effective strategy for enzyme immobilization and cascade system construction, promoting its potential applications in biosensing.