Optimizing the Coordination Structure of Quasi Fe MIL-101 for a Colorimetric Biosensing Platform to Detect Galactose

A major hurdle in nanozyme design is the difficulty of rationally tuning the coordination and electronic states of active sites, which are typically locked by the material's rigid framework or surface composition. In this study, we address this limitation by developing a series of Fe-based quasi metal-organic framework nanozymes having a succulent appearance, denoted as Q_x-MIL, through controlling the calcination of MIL. Partial decomposition of terephthalic acid ligands during heating increases the electron density of Fe active centers, reduces their coordination number, and generates asymmetric unsaturated Fe sites. These structural modifications enhance electron transfer, improve intermediate adsorption, promote the hydroxyl radical formation, and lower the energy barrier of the rate-determining step. As a result, Q₄₀₀-MIL exhibits remarkable peroxidase-like activity and enhanced reaction kinetics. Leveraging this superior enzyme-mimicking performance, we constructed a galactose-oxidase-cascade colorimetric biosensor for the sensitive and selective detection of galactose. This work not only validates the high enzymatic activity and bioapplication potential of quasi MOF nanomaterials but also provides a simple and effective strategy for precisely engineering the active sites of nanozymes to broaden their functional scope.