Synergistic "capture-and-catalysis" at a V₂O₃@NC/NHCS composite interface for the ultrasensitive electrochemical...

Amaranth (AM) is a widely used synthetic azo food colorant that poses severe toxicological risks upon excessive consumption, creating an urgent need for its ultra-sensitive detection. We report a high-performance electrochemical sensor based on the electrostatic co-aggregation of V₂O₃@NC and NHCS for the high-fidelity quantification of AM. A unique "capture-and-catalysis" synergistic mechanism governs this composite interface. Specifically, the highly porous NHCS framework provides exceptional capacity to capture and pre-concentrate target molecules while acting as a highly conductive "electronic bridge." Subsequently, the abundant mixed-valence (V³⁺/V⁵⁺) sites of the V₂O₃@NC serve as a robust electrocatalytic engine to drive the catalysis, significantly amplifying the AM oxidation signal. Combining electrochemical kinetic analysis with DFT calculations (including HOMO and MEP), we reveal that this electrocatalytic evolution proceeds via a directional 1 H⁺/2e^- transfer mechanism. Under optimal conditions, the V₂O₃@NC/NHCS sensor exhibits a broad linear range (0.01-12 µM) and an extremely low LOD of 0.80 nM. Practical analysis of commercial beverages yielded recoveries of 95.0%-104.3%, with results perfectly matching orthogonal UV-Vis cross-validation. This work provides a robust platform for azo dye screening and profound insights into the rational design of "capture-and-catalysis" composite interfaces.