Red-emission carbon dots-quercetin systems as ratiometric fluorescent nanoprobes towards Zn2+ and adenosine triphosphate

Abstract

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 Zn2+ was further introduced, the QCT-Zn2+ 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-480/I-610) gradually increases with increasing concentration (c) of Zn2+. Al3+ exhibits the same phenomen like Zn2+. Fluoride ions form a more stable complex with Al3+ than QCT-Al3+ complex but have a negligible effect on the QCT-Zn2+ complex. The possible interference of Al3+ on Zn2+ can thus be avoided by adding certain amount of F-. The CD-QCT-F- system was constructed as a ratio-metric fluorescent nanoprobe toward Zn2+ with determination range of 0.14-30 mu M and limit of detection (LOD) of 0.14 mu M. Due to the stronger affinity of adenosine triphosphate (ATP) to Zn2+ than QCT, the I-480/I-610 value of CD-QCT-F--Zn2+ system gradually decreases with increasing c(ATP). The ratiometric fluorescent nanoprobe toward ATP was established with detection ranges of 0.55-10 and 10-35 mu M and a LOD of 0.55 mu M. The above two probes enable the quantitative determination of Zn2+ and ATP in tap and lake water samples with satisfactory recoveries. Schematic representation of the ratiometric fluorescent nanoprobes based on the carbon dots (CDs)-quercetin (QCT) system towards Zn2+ and adenosine triphosphate (ATP) with high selectivity and sensitivity.