Ultrasensitive and selective detection of Cu2+ in aqueous solution with fluorescence enhanced CdSe quantum dots

Trace Cu2+ ions in aqueous solution were detected with ultra-sensitivity and excellent selectivity by using CdSe quantum dots (QDs) with enhanced fluorescence properties as fluorescent reporters. CdSe QDs were first synthesized by using aqueous route with 3-mercaptopropionic acid (3-MPA) as capping agent. By further thermal-annealing the as-prepared 3-MPA capped CdSe QDs in the presence of imidazole (IM) under nitrogen atmosphere at 70 °C, the fluorescence quantum yields of CdSe QDs in aqueous solution could be dramatically enhanced to be ∼10.9%. These CdSe QDs with enhanced fluorescence exhibited fast fluorescence response (within 1 min), ultra-sensitivity and excellent selectivity toward Cu2+ ions over other metal ions in aqueous solution. The Cu2+-induced aggregation of CdSe QDs led to the significant fluorescence quenching of the CdSe QDs. The limit of detection (LOD) calculated for Cu2+ could reach as low as 0.13-0.16 ppb (2.0-2.5 nM). The co-existence of other metal ions did not interfere with the sensing of trace Cu2+ ions in aqueous solution.