Nitrogen-doped carbon dots as a probe for the detection of Cu²⁺ and its cellular imaging

Nitrogen-doped carbon dots were synthesized using citric acid monohydrate and glutathione as raw materials. The synthesized nitrogen-doped carbon dots were characterized by multiple analytical techniques, including transmission electron microscopy, Fourier transform infrared spectroscopy, ultraviolet–visible absorption spectroscopy, X-ray photoelectron spectroscopy, X-ray diffractometry, and fluorescence spectra. The fluorescence intensity of the nitrogen-doped carbon dots gradually quenched with different concentrations of Cu²⁺ ions. The effect of the pH value, the nitrogen-doped carbon dot concentration, and the reaction time on the fluorescence intensity of the N-CDs-Cu²⁺ system was investigated, and the experimental conditions were optimized. A rapid and sensitive method for the determination of Cu²⁺ ions was established that exhibited a good linearity in the concentration range 0.20–200.0 μM with a detection limit of 0.27 nM. Meanwhile, the fluorescence quenching mechanism of the interaction between nitrogen-doped carbon dots and Cu²⁺ was preliminarily discussed. The method was used to detect trace Cu²⁺ in tap water and lake water, with recoveries ranging from 98.1% to 102.0%. Furthermore, due to low cytotoxicity and good biocompatibility, nitrogen-doped carbon dots as a probe were also successfully used in bioimaging.