Fluorimetric and colorimetric analysis of total iron ions in blood or tap water using nitrogen-doped carbon dots with tunable fluorescence

Fluorimetric and colorimetric analysis strategies have been developed for simultaneously probing Fe3+ and Fe2+ ions in blood or tap water using nitrogen-doped carbon dots (N-Cdots). Herein, the N-Cdots were prepared using melamine by a neutralization heat reaction one-step synthesis route showing high aqueous solubility and environmental stability. Importantly, unlike common carbon dots (Cdots) that generally display one emission of blue fluorescence, they can display excitation-dependent tunable emissions. Moreover, the bright blue-green fluorescence of N-Cdots could be specifically quenched by Fe3+ or Fe2+ ions simultaneously, showing a color change. Herein, the fluorescent quenching of N-Cdots is thought to result from the aggregation of N-Cdots triggered by the unique coordination interactions between Fe3+ or Fe2+ ions and amine and amide groups of N-Cdots. The developed analysis strategies were employed for the evaluation of the total iron levels in blood or tap water, with a detection limit down to about 5.0 nM, exemplified for Fe3+ ions. These strategies could be promising for use in practical applications for the clinical diagnosis of iron-relative diseases (i.e., anemia and cancers) and environmental monitoring of iron pollution. In addition, this one-step neutralization heat reaction route as a facile green synthesis candidate may be tailored for the fabrication of a variety of Cdots, especially those with doped heteroatoms (i.e., nitrogen) for extensive applications in biomedical and environmental fields.