Red-emission carbon dots-quercetin systems as ratiometric fluorescent nanoprobes towards Zn and adenosine triphosphate.

Carbon dots (CDs) emitting red fluorescence (610 nm) were synthesized by solvent thermal treatment of p-phenylenediamine in toluene. Upon 440 nm excitation, quercetin (QCT) alone endowed slight effects on the red fluorescence of CDs. Once Zn was further introduced, the QCT-Zn complex was quickly formed. This complex absorbs excitation light and emits bright green fluorescence at 480 nm. The red fluorescence of CDs was greatly quenched owing to the inner-filter effect. The ratio of fluorescence intensity at 480 nm and 610 nm (I/I) gradually increases with increasing concentration (c) of Zn. Al exhibits the same phenomen like Zn. Fluoride ions form a more stable complex with Al than QCT-Al complex but have a negligible effect on the QCT-Zn complex. The possible interference of Al on Zn can thus be avoided by adding certain amount of F. The CD-QCT-F system was constructed as a ratio-metric fluorescent nanoprobe toward Zn with determination range of 0.14-30 μM and limit of detection (LOD) of 0.14 μM. Due to the stronger affinity of adenosine triphosphate (ATP) to Zn than QCT, the I/I value of CD-QCT-F-Zn system gradually decreases with increasing c. The ratiometric fluorescent nanoprobe toward ATP was established with detection ranges of 0.55-10 and 10-35 μM and a LOD of 0.55 μM. The above two probes enable the quantitative determination of Zn and ATP in tap and lake water samples with satisfactory recoveries. Graphical abstract Schematic representation of the ratiometric fluorescent nanoprobes based on the carbon dots (CDs)-quercetin (QCT) system towards Zn and adenosine triphosphate (ATP) with high selectivity and sensitivity.