Lemon juice-derived nitrogen-doped carbon quantum dots for highly sensitive and selective determination of ferrous ions and cell imaging

Ferrous ion (Fe²⁺) plays an important role in a large number of chemical and biological processes in living organisms. So, the accurate and rapid determination of Fe²⁺ in environmental and biological systems is an important issue. In this paper, N-CDs with uniform particle size, outstanding water solubility, favorable stability, high quantum yield (QY, 58.66 %) and excellent photoluminescence performance were prepared by one-step hydrothermal method using biomass lemon and ethylene diamine. The N-CDs showed a bright blue fluorescence under UV light. This new type of N-CDs can be used to effectively detect Fe²⁺ with high selectivity and sensitivity. It displayed a fine linear relationship in the range of 2–625 μΜ with the LOD of 0.063 μM under optimum conditions. The possible fluorescence quenching mechanism can be ascribed to the static quenching (SQ) and internal filtration effect (IFE) for Fe²⁺. More importantly, the optical imaging performance and cytotoxicity of N-CDs were also demonstrated. The results showed that N-CDs owned low cytotoxicity and glorious biocompatibility, and could be used as a biological imaging agent for labeling Hela cells. Therefore, this study possesses expansive application prospects in environmental monitoring and bioanalysis.