Two of a kind but different: Luminescent carbon quantum dots from Citrus peels for iron and tartrazine sensing and cell imaging.

Citrus sinensis and Citrus limon peels were used to synthesize two different kinds of carbon quantum dots (CQDs) via an unsophisticated and inexpensive carbonization procedure. The proposed synthesis is straightforward and adheres to the principles of green chemistry since no organic solvents are used and no toxic by-products are formed, while the residual resources employed facilitate the large scale synthesis of dots. The Citrus sinensis and Citrus limon peels are proved to be excellent precursors for the synthesis of CQDs with highly practical applications. The CQDs display strong excitation-independent, blue fluorescence, which is stable over time. Splendid water dispersibility, photostability and stability over a wide range of pH are some of the main advantages of the CQDs, which enable them to be used as a fluorescent probes. Although many of their features are alike, our findings demonstrate that each kind of the CQDs lend itself to quite distinct analytical applications. The developed fluorescent probes possess high potential for sensitive and selective detection of Fe3+ (Citrus sinensis CQDs) and tartrazine (Citrus limon CQDs) via a quenching mechanism. The decrease in fluorescence intensity is in linear relationship with the concentrations of Fe3+ and tartrazine in the ranges of 0.01–1.0μM and 0.6–23.5μΜ, respectively. Moreover, their low cytotoxicity reinforces their applicability towards cell bioimaging and intracellular detection of Fe3+, which were further studied.