Novel single excitation dual-emission carbon dots for colorimetric and ratiometric fluorescent dual mode detection of Cu and Al ions

In this study, dual-emission carbon dots (D-CDs) are synthesized via a simple one-step solvothermal treatment of red tea. The obtained D-CDs are characterized by XPS, IR, TEM, XRD, fluorescence and UV-vis spectroscopy techniques. It is found that D-CDs present a strong red fluorescence emission peak at 671 nm and weak blue fluorescence emission peak at 478 nm under the excitation wavelength of 410 nm. The unique dual-emission properties of D-CDs provide great opportunities in ratiometric fluorescence sensing applications. The results show that Cu 2+ ions can quench the fluorescence of the red emission band of D-CDs effectively, resulting in the disappearance of red fluorescence ultimately. Upon the addition of Al 3+ ions, the fluorescence of blue emission band at 478 nm grows apparently, and the fluorescence color transforms gradually from red to orange, then to yellow-green. Based on these findings, a novel ratiometric fluorescence and colorimetric dual mode nanosensor is developed for simultaneous detection of Cu 2+ and Al 3+ ions. Regarding Cu 2+ ions, the fluorescent detection linear range is 0.1-50 μM with detection limit of 0.1 μM, and the colorimetric detection limit is estimated as 25 μM. With regard to Al 3+ ions, the fluorescent detection linear range is 0-20 μM and 25-100 μM with detection limit of 0.5 μM, and the colorimetric detection limit is 20 μM. Furthermore, the fluorescence response mechanisms of Cu 2+ and Al 3+ ions were discussed detailed. To the best of our current knowledge, this will be the first research work on the simultaneous determination of Cu 2+ and Al 3+ using D-CDs as fluorescent probes. D-CDs with strong red emission and weak blue emission as an effective colorimetric and ratiometric fluorescence sensing probe are employed to realize the simultaneous detection of Cu 2+ and Al 3+ ions without any interference effect.