A quantum dot-based dual fluorescent probe for recognition of mercuric ions and N-acetylcysteine: “On–Off–On” approach
A mercaptopropionic acid-capped cadmium sulfide quantum dot (MPA-CdS QD) based dual fluorescent “On–Off–On” probe was designed and applied for sensitive and selective monitoring of mercuric ions (Hg2+) and N-acetylcysteine (NAC) in aqueous solution. In the mercuric ion detection, the fluorescence of MPA-CdS QDs decreased with increasing amount of Hg2+. This is because of the binding of mercuric ions to mercaptopropionic on the surface of quantum dots and the electron transfer from the photoexcited MPA-CdS QDs to mercuric ions. Subsequently, upon the successive addition of NAC, the fluorescence of MPA-CdS QDs is recovered due to the high binding affinity of NAC with mercuric ions; NAC can form a more stable complex with mercuric ions in aqueous solution, and this releases the fluorescent MPA-CdS QDs. The strategy was simply achieved by measuring the changes in the fluorescence intensity of QDs. The present results suggest that the developed method has several advantages such as being simple, straightforward, and highly sensitive, ease of operation and cost effectiveness and is used for simultaneous determination of two analytes in aqueous media. The linear response range was obtained over the range of 25–225 ng mL−1 and 0.05–0.9 μg mL−1 with a low detection limit of 25.2 ng mL−1 and 0.092 μg mL−1 for Hg2+ ions and NAC, respectively. The developed probe was successfully applied for the determination of Hg2+ and NAC in real samples with satisfactory results.