Regulating relative nitrogen locations of bipyridine covalent organic frameworks with enhanced peroxidase-like activity for biosensing.

Since metal-based enzyme mimics can raise biosafety concerns due to potential toxicity accumulation, it is necessary to develop metal-free alternatives that exhibit high catalytic efficiency and enhanced selectivity. Herein, we report the development of bipyridine-bridged covalent organic frameworks (COFs) exhibiting peroxidase-like (POD-like) activity as intelligent artificial enzymes for biomarker detection. Their catalytic function is enabled by a facile strategy that modulates charge transfer within the framework through precise regulation of the nitrogen site in the bipyridine units. The nitrogen-modulated of charge transfer directionality intensified with increasing D-A contrast in Bpy-COF than PyIm-COF, resulting in a more efficient POD-like biocatalytic activity. The Bpy-COF exhibit favorable Michaelis-Menten kinetics than PyIm-COF. Moreover, the Bpy-COF show tunable biocatalytic detection capabilities, which outperform the recently reported state-of-the-art POD-mimics regarding biosensing efficiency. Remarkably, the Bpy-COF exhibits efficient measurement of α-glucosidase (α-Glu) with the extremely low limit of detection (LOD), facilitating its application in biomarker analysis. This work not only introduces a unique metal-free biocatalyst for highly sensitive and low-cost colorimetric assays but also provides valuable insights for developing advanced enzyme-mimicking COF materials through nitrogen-modulation strategies.