Micellar extraction assisted fluorometric determination of ultratrace amount of uranium in aqueous samples by novel diglycolamide-capped quantum dot nanosensor

Uranium (U), the naturally occurring toxic radionuclide is soluble in aquatic environment as uranyl ion (UO22+) and hence bioavailable U can affect living organisms adversely. Detection of U in aqueous samples was made simple, cost effective and sensitive by synthesizing a highly specific diglycolamide-capped CdS/ZnS core-shell quantum dot (QD) nanosensor. Its ultratrace level determination was done by conjugating this nanosensor with cloud point extraction (CPE) procedure. In solution the UO22+ ion gets bonded to the diglycolamide group of the QD nanosensor and a direct Föster Resonance Energy Transfer (FRET) mechanism takes place between the UO22+ ion and QD. This results in increase of the QD fluorescence intensity and the phenomenon was used to detect the metal ion concentration. The dynamic linear range (DLR) of the method was found to be 1.0–100 ng mL−1 of U in water. The limit of detection (LOD) was found to be 0.03 ng mL−1. The developed methodology was validated by measuring the value of U in NIST SRM 1640a which was found to be in agreement with the reported value at 95% confidence level. The method was successfully applied to the U determination in three natural water samples with ≤5% of relative standard deviation (RSD, 1σ).