Ultrasensitive Pb2+ detection based on fluorescence resonance energy transfer (FRET) between quantum dots and gold nanoparticles

Positively charged CdTe-QDs capped with cysteamine (CA-CdTe-QDs) and negatively charged AuNPs capped with 11-mercaptoundecanoic acid (MUA-AuNPs) have been prepared. They are water-soluble and biocompatible. An assay for the determination of Pb2+ has been proposed based on the modulation in FRET efficiency between QDs and AuNPs in the presence of Pb2+, which inhibits the interaction of the QD-AuNP assembly. This method is easy to operate and with remarkably high sensitivity. Under the optimum conditions, the response is linearly proportional to the concentration of Pb2+ in the range 0.22-4.51 ppm, and the detection limit is found to be 30 ppb of Pb2+ due to the superior fluorescence properties of QDs. The mechanism of this strategy is also discussed.