Glucose oxidase immobilized on ZIF-7-III: composite formation, optimization and integration in an electrochemical biosensor for selective glucose detection

Coordination polymers (CPs) can be used as supporting materials for enzyme immobilization to overcome limitations arising from mass transfer barriers, active site blocking, and low enzyme loading, as previously demonstrated, employing metal-organic frameworks (MOFs). We report on a new composite containing glucose oxidase (GOD) and ZIF-7-III (Zn(bIm)₂), focusing on three aspects: formation, optimization of catalytic properties, and application. The immobilization of GOD on ZIF-7-III at room temperature was systematically studied by varying the amount of GOD and the reaction time. ZIF-7-III/GOD composites were obtained, as confirmed by Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). GOD incorporation significantly slows the crystallization of ZIF-7-III. The optimized composite exhibits relative catalytic activity of 98% at maximum enzyme loading, enhanced stability across a broad pH range (3 < pH < 9), and stability at elevated temperatures (up to 80 °C). Storage stability retains 66% activity after 60 days, which is important for possible applications. The use of the composite in an electrochemical biosensor for glucose detection was also demonstrated. Cyclic voltammetry and amperometric measurements were performed, demonstrating high repeatability (RSD <6%) and selectivity against common interferents. A linear response to glucose concentrations in the millimolar range was observed, with a detection limit of 0.01 mmol L^-1. Notably, the sensor effectively detected glucose in human plasma samples, indicating its potential for real-world glucose monitoring.