Novel single excitation dual-emission carbon dots for colorimetric and ratiometric fluorescent dual mode detection of Cu(2+) and Al(3+) 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.