One Nanozyme, Three Functions: Substrate-Switchable Cu– NH₂–BDC nanozyme for Multiplexed Biosensing in Physiological Environments

Nanomaterials with multifunctional enzyme-like activities hold great promise for next-generation biosensing technologies. Here, we report an amino-functionalized copper-based metal–organic framework (Cu–NH₂–BDC) that integrates intrinsic fluorescence with versatile catalytic functions, including oxidase (OXD), peroxidase (POD), and laccase (LAC) activities. Engineering amino group and the central metal node enables Cu–NH₂–BDC to overcome the intrinsic pH limitations of most nanozymes, achieving its highest catalytic efficiency at physiological pH (7.4). Remarkably, Cu–NH₂–BDC exhibits substrate-switchable catalytic behavior, in which the substrate itself directs the dominant enzymatic pathway. This unique mechanism allows precise regulation of enzyme-mimetic activity while minimizing interference among multiple catalytic modes. Leveraging these properties, we established a triple-mode biosensing platform capable of highly sensitive and selective detection of acetylcholinesterase (AChE; LOD = 0.001 mU/mL), dopamine (DA; LOD = 0.048 μg/mL), and ascorbic acid (AA; LOD = 0.6 μM) under physiological conditions. This work introduces a novel substrate-engineering strategy for modulating multi-enzyme activities in nanozymes and provides a powerful and generalizable approach for developing intelligent multifunctional biosensors.