Mechanistic Insights Into Selective Sensing Of Pb2+ In Water By Photoluminescent Cds Quantum Dots

The prospect of aqueous polyethyleneimine-capped CdS quantum dots (QDs), in toxic metal-ion sensing, has been explored. Pb2+ binds strongly to the surface of the QDs facilitating ultrafast electron transfer. As a result, severe (similar to 90%) PL quenching is observed. Hot electron transfer plays an important role in the quenching process, as is elucidated by anticorrelation between the magnitude of ground-state bleach of the QDs and the concentration of Pb2+ ions, as well as the concurrent decrease in bleach rise time. A second major contribution is from electron transfer from conduction band edge, with a rate constant of 1.45 x 10(11) s(-1). Selectivity in this "turn-off" sensing process is governed by the exergonicity, quality of QD surface, nature of capping ligand, and its metal-ion binding properties. Engineering these factors is crucial for the development of QD-based selective and efficient metal-ion sensors.