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-Al3+) can efficiently coordinate on the surface of CNDs, the emission of CNDs at 429 nm completely overlapped with the absorption peak of QCT-Al3+ at 428 nm. Therefore, a ratiometric fluorescence sensor for Al3+ was developed based on fluorescence resonance energy transfer (FRET) with CNDs as donor and QCT-Al3+ as acceptor. A linear calibration of F429/F481 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-Al3+ was applied for fluorescent test papers with satisfying resolution.