Oxidase-mimicking bimetallic doped carbon quantum dots for mechanistically resolved dual-mode determination of tert-butylhydroquinone in edible oils.

Abstract

A sensitive dual-mode colorimetric-fluorometric platform was developed for the determination of tert-butylhydroquinone (TBHQ) in edible oils using nickel-copper co-doped carbon quantum dots (NiCu@CQDs). The NiCu@CQDs were synthesized through a facile one-step hydrothermal method and exhibited uniform morphology, strong blue fluorescence at 470 nm, a high quantum yield of 43.86%, and excellent optical and storage stability. Owing to their oxidase-mimicking activity, NiCu@CQDs activated dissolved oxygen to generate superoxide radicals (O₂•⁻), thereby catalyzing the oxidation of TBHQ to 2-tert-butyl-1,4-benzoquinone (TBBQ). The resulting quinone subsequently reacted with ethylenediamine (EDA) to form an orange chromophore with a characteristic absorption maximum at 482 nm. Simultaneously, this product quenched the fluorescence of NiCu@CQDs through the synergistic contributions of Förster resonance energy transfer and the inner-filter effect, with the latter serving as the dominant pathway. Under optimized conditions, the colorimetric assay exhibited a linear response over 0.1-580 µM with a detection limit of 0.024 µM, whereas the fluorometric mode provided a wider linear range of 0.02-600 µM and a lower detection limit of 0.0048 µM. The platform demonstrated excellent selectivity against structurally related antioxidants and common oil constituents, retained its catalytic activity for 75 days, and showed satisfactory batch-to-batch reproducibility (RSD ≤ 3.45%). Application to olive, grapeseed, rapeseed, and soybean oils yielded recoveries of 91.6-109.0% with RSDs of 2.67-5.23%, in good agreement with the reference HPLC method. These findings establish NiCu@CQDs as a robust multifunctional nanozyme for rapid, sensitive, and reliable TBHQ monitoring in complex food matrices.

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