Electrochemical Gating of d-Band Engineering in Hierarchically Bridged Dual-Site Nanozymes for Synergistic Cascade Catalysis and Wearable Biosensing.

Cascade nanozymes for biosensing are fundamentally hampered by diffusion limitations and passive catalytic sites. Herein, we report a strategy of electrochemical gating of d-band engineering within a hierarchically bridged dual-site nanozyme (CuNCs@FeMOP) to achieve dynamic control over cascading catalysis. This architecture spatially confines the ascorbic acid oxidase-mimicking copper nanocluster (CuNC) core and the peroxidase-mimicking iron-based microporous organic polymer (FeMOP) shell, eliminating intermediate diffusion losses. More critically, synergistic electronic coupling via a histidine bridge provides static preoptimization of the Cu and Fe sites' d-band structure, enhancing their intrinsic activities. Upon this foundation, an external electric field acts as a dynamic gate, further modulating the d-band centers of both Cu and Fe sites to synchronously amplify their respective catalytic activities. This dual-mode d-band engineering endows the CuNCs@FeMOP system with exceptional Michaelis-Menten kinetics (low Km, high Vmax) far surpassing conventional mixed-catalyst systems. The nanozyme was integrated into a flexible patch for the real-time, colorimetric/electrochemical dual-mode monitoring of ascorbic acid in human sweat, demonstrating its practical utility. This work introduces a paradigm for catalyst design, where gated d-band engineering in bridged, multisite architectures enables programmable control over catalytic processes for advanced wearable diagnostics.