Water-soluble CdTe quantum dots (QDs) have been utilized as photoluminescence probes for the detection of metal ions such as Pb2+, Hg2+, Cd2+, etc. We initially developed highly photoluminescence (PL) Zn-doped CdTe for toxic ions detection. A study on the changes of optical properties of Zn-doped CdTe and CdTe QDs when exposed to Pb2+ suggested that Pb2+ could act as a surface passivating agent to reduce Te2- dangling bonds while Zn2+ dopant stabilizes the QDs surface against ambient oxidation. The results demonstrated herein provide useful understandings of the interactions between water-soluble QDs and metal ions. These results suggest further applications of QDs in sensing metal ions.