Highly fluorescent nitrogen-doped carbon dots for selective and sensitive detection of Hg2+ and ClO− ions and fluorescent ink

A facile one-step hydrothermal strategy using citric acid, ethylenediamine, and fluorescein as the precursors for the synthesis of fluorescent nitrogen-doped carbon dots (NCDs). The obtained NCDs exhibited blue fluorescence with maximum excitation/emission wavelengths at 350/447 nm and fluorescence quantum yield was up to 61%. The blue emission of the NCDs was independent of the excitation wavelength from 330 to 390 nm, while they possessed spherical morphology. The NCDs were also very stable in a wide pH range and in solutions with high ionic strength. More specifically, the fluorescence of the NCDs was effectively quenched by mercuric (Hg2+) and hypochlorite (ClO−) ions, suggesting that the NCDs can be utilized for detecting Hg2+ and ClO− with high selectivity and sensitivity. The linear ranges and limits of detection were 0.05–30 μM and 19 nM for Hg2+, and 0.1–70 μM and 90 nM for ClO−, respectively. Moreover, the NCDs were applied for detecting Hg2+ and ClO− in water samples with satisfactory results, indicating its sensing potential in environmental monitoring. Additionally, it was proven that the synthesized NCDs could be utilized as a fluorescent ink.