Bifunctionality of enhanced stability and synergistic catalysis for natural enzyme based on bimetallic zeolitic imidazolate framework

Natural enzyme-based immunoassays are most widely used in clinical researches and diagnostics. Although 80% immunoassays involve the use of natural horseradish peroxidase (HRP), this enzyme suffers from low stability and storage problems, limiting its further applications. In this work, by considering the interactions between Fe element and the heme ring of the active center of HRP, we synthesized a bimetallic FeZn-zeolitic imidazolate framework (FeZn-ZIF) to synergistically provide enhanced stability and catalysis for HRP. Under a mild one-pot synthesis process with the effect of Fe element, HRP encapsulated in bimetallic FeZn-ZIF exhibited a 114-fold and a 21.3-fold higher initial catalytic rate and apparent activity than those of HRP encapsulated in pristine ZIF-8. Importantly, HRP@FeZn-ZIF showed excellent stability under the various conditions such as the storage of day and temperature, pH, the physicochemical process of freeze-thaw cycle, shaking, sonicating and organic solvents. Immunoassays involving HRP@FeZn-ZIF as promising probe for digoxin detection was successfully established to demonstrate its potential application, which showed widely a dynamic range from 10 pg/mL to 500 ng/mL, good anti-interference capability, and a reliable recovery (relative standard deviation below to 6.4%). Under the bifunctionality of enhanced stability and synergistic catalysis based on bimetallic FeZn-ZIF, HRP might be explored further application even in harsh environments.