An ultrasensitive fluorescent probe is developed for the determination of lead ion by utilizing dithizone (Dz) functionalized CdSe/CdS quantum dots (QDs). Dithizone was bound to the QDs via a surface coordinating reaction to form QDs-Dz conjugates and quench fluorescence of the QDs by fluorescence resonance energy transfer (FRET) mechanism. Upon the addition of Pb2+, a dramatic enhancement of the fluorescence intensity was observed, which resulted from the FRET pathway shutting off, and hence the fluorescence of the QDs was recovered. Two successive linear ranges of 0.01 - 1000 nmol L-1 and 1-20 mu mol L-1 allow a very wide determination of Pb2+ concentration from 0.01 nmol L-1 to 20 mu mol L-1, with a detection limit of 0.006 nmol L-1. The fluorescent probe was successfully applied to the determination of lead in environmental samples with satisfactory results. (C) 2013 Elsevier B.V. All rights reserved.