Carbon nanodots functionalized with rhodamine and poly(ethylene glycol) for ratiometric sensing of Al ions in aqueous solution

Carbon nanodots (CDs) functionalized with a rhodamine moiety and poly(ethylene glycol) (PEG) were used for selective fluorometric detection of Al ions. When the Al ion was exposed to the modified CDs, the lactam ring of the rhodamine moiety opened and, subsequently, was ready to absorb the emission of CDs, leading to a Förster resonance energy transfer (FRET)-based sensing protocol in aqueous media. A selective response to Al ion was observed in an aqueous solution, which was attributed to the ability of the rhodamine moiety to interact with the Al ion, but not with other metal ions. PEG played a role in improving the water-solubility of rhodamine-appended CDs that were intrinsically hydrophobic. The FRET-based mechanism provideed a ratiometric sensing that could remove possible interference via self-calibration of two emission bands.