Cerium-based metal-organic framework nanozyme with high oxidase-like activity at neutral pH for discrimination and detection of antioxidants

Oxidase-mimicking nanozymes have witnessed extensive applications in biosensing, however, a huge shortcoming is their activity limited by acidic conditions. Herein, a Ce-MOF containing hexanuclear clusters was developed, which exhibited robust oxidase-like activity at neutral pH (0.97 U mg-1) with the extremely high affinity for 3,3 ',5,5 '-tetramethylbenzidine (TMB) (Km: 0.012 mM) and wide temperature adaptability (0-50 degrees C). Experiment screening and theoretical calculations revealed that the high activity was derived from unsaturated CeIV active sites and the redox cycling of unique Ce4+/Ce3+ node. These factors endow Ce-MOF generating more O2 center dot- species and significantly reducing the energy barrier of the rate-controlling step in the catalytic process. Given the exceptional activity for two chromogenic substrates, a two-channel colorimetric array is constructed to successfully distinguish four antioxidants. The detection was operated within 2 min in ultrapure water at room temperature, showing excellent convenience and efficiency. This study carries significant implications for developing oxidase-mimics with high activity under neutral pH and constructing simple and practical platforms to identify antioxidants in complex samples.