High-quantum Yield Carbon Dots as Selective Fluorescence Turn-off Probe for Bromate Detection in Food Samples Via Catalytic Oxidation Mechanism.

In this study, nitrogen-doped carbon dots (N-CDs) were successfully synthesized through a facile one-step hydrothermal approach using honeysuckle and ethylenediamine (EDA) as carbon and nitrogen sources, respectively. The obtained N-CDs displayed intense blue fluorescence emission at 420 nm upon excitation at 350 nm, along with an exceptional fluorescence quantum yield of 60.53%. Systematic characterization experiments employing transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) revealed the morphological features, surface functional groups, and elemental composition of the N-CDs. Remarkably, in HCl medium, chloride ion-catalyzed bromate oxidation led to pronounced fluorescence quenching of the N-CDs. A highly linear correlation (R² = 0.9965) was found between bromate concentration (64-1024 ng·mL) and fluorescence quenching efficiency, as quantified by the equation log(I₀/I) = 3.86685C + 0.00557, with an impressive detection limit of 14 ng·mL (S/N = 3). The practical application of this sensing platform to bromate determination in flour-based food products and tap water samples yielded satisfactory recoveries, ranging from 87.4 to 104.4%, with relative standard deviations below 3.5%. These findings highlight the great potential of the as-synthesized N-CDs as a reliable fluorescent nanoprobe for sensitive and selective bromate detection in complex food and environmental samples.