Green synthesis of fluorescent carbon nanospheres from chrysanthemum as a multifunctional sensor for permanganate, Hg(II), and captopril.

A simple and green method for the synthesis of fluorescent carbon nanospheres (CNs) was proposed using chrysanthemum as a natural precursor and ethylenediamine as the co-reagent. The prepared CNs show strong blue fluorescence in water with quantum yield of 13.7 %, and distinguished fluorescent stability against photobleaching and ion strength. Meanwhile, the fluorescence signal of CNs is reversible and sensitive to temperature in the range of 20-80 °C, which makes CNs useful as a temperature sensor. More importantly, the CNs can serve as excellent fluorescent sensors for detecting MnO4- and Hg2+ with the detection limit of 0.72 and 0.26 μM, respectively. MnO4- quenches the fluorescence of CNs through inner filter effect and static quenching mechanism, while Hg2+ forms a stable complex with the amino group on the surface of CNs, resulting in the fluorescence quenching of CNs. However, the stronger affinity between Hg2+ and captopril (Cap) results in the fluorescence quenched by Hg2+ recovery after the addition of Cap. Thus, the CNs-Hg2+ system is employed as a novel sensitive and selective fluorescence "turn-on" sensor for Cap in the range of 0-75 μM. Inspired by the sensing results, the developed sensors were successfully used for the determination of MnO4-, Hg2+ in river water samples and Cap in the pharmaceutical and urine samples.