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 degrees C, the fluorescence quantum yields of CdSe QDs in aqueous solution could be dramatically enhanced to be similar to 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. (C) 2013 Elsevier B. V. All rights reserved.