High photoluminescent carbon nanodots and quercetin-Al3+ construct a ratiometric fluorescent sensing system

Highly blue fluorescent carbon nanodots (CNDs) were synthesized by the hydrothermal method from citric acid and diethylenetriamine with the quantum yield of about ∼86%. Quercetin (QCT) and its fluorescent metal-ion complex (QCT-Al 3+ ) can efficiently coordinate on the surface of CNDs, the emission of CNDs at 429   nm completely overlapped with the absorption peak of QCT-Al 3+ at 428   nm. Therefore, a ratiometric fluorescence sensor for Al 3+ was developed based on fluorescence resonance energy transfer (FRET) with CNDs as donor and QCT-Al 3+ as acceptor. A linear calibration of F 429 / F 481 versus aluminum ion concentration was obtained within 1–20 and 20–60   μM, along with a detection limit of 558   nM. Moreover, the ESIPT–FRET ratiometric fluorescence system based on the CNDs/QCT-Al 3+ was applied for fluorescent test papers with satisfying resolution.