Cu,Fe,B/Cur-CDs with peroxidase- and ascorbic acid oxidase-like catalytic activity for dual-signal fluorescence sensing of metronidazole

A curcumin based iron, copper and boron doping carbon dots (Cu,Fe,B/Cur-CDs) with ascorbic acid oxidase (AAO)- and peroxidase (POD)-like activities were synthesized via microwave digestion. The Cu,Fe,B/Cur-CDs oxidize ascorbic acid (AA) to dehydroascorbic acid (DHAA), which reacts with o -phenylenediamine (OPD) to generate fluorescent 3-(1,2-dihydroxyethyl) furo [3,4-b]quinoxaline-1-one (DFQ). Simultaneously, it catalyzes OPD/H₂O₂ to fluorescent 2,3-diaminophenazine (DAP) via POD-like activity. In the presence of metronidazole (MNZ), it induces competitive inhibition by competing with OPD for the active sites of Cu, Fe, B/Cur-CDs. This reduces the generation of •OH and •O₂ − radicals, hindering the oxidation of OPD to form DAP and thus decreasing the system's fluorescence intensity. Additionally, MNZ quenches the fluorescence of DFQ at 420 nm via the inner filter effect. Therefore, a dual-signal fluorescence sensor for MNZ detection was constructed. The sensor achieved 91.6–109.9 % and 86.2–116.2 % recovery in food samples using standard addition, demonstrating high sensitivity for dual-signal detection systems.