Selective and sensitive detection of Cu2+ ions in the midst of other metal ions using glutathione capped CuInS2/ZnS quantum dots

We herein report a facile fluorometric method for the detection of Cu2+ ions by using water-soluble glutathione (GSH) capped ternary CuInS2/ZnS (CIS/ZnS) quantum dots (QDs). The as-synthesized QDs are similar to 3.2 nm in diameter, nearly spherical in shape and fluorescent in the red region. Photostability studies revealed that the assynthesized CuInS2/ZnS QDs maintained 70% of their initial fluorescence after hours of irradiation while the pH analysis showed that the QDs fluorescent emission was stable within the pH 4-11 with maximum stability at pH 6. The fluorometric analysis revealed that the QDs undergoes remarkable photoluminescence quenching in the presence of Cu2+ ions compared to other metal ions such as Hg2+, Co2+, Cd2+, Pb2+, Zn2+, Ni2+, Mg2+, Sn2+, Mn2+, Fe2+, Fe3+ ions. The Fourier transform infra-red (FTIR) spectroscopy, Dynamic light scattering (DLS) and transmission electron microscopy (TEM) analyses revealed that the quenching could be attributed to the aggregation of QDs due to the complexation of Cu2+ ions with the GSH capping group of the QDs. The fluorescence quenching of CIS/ZnS QDs exhibited linear response against Cu2+ ions in the concentration range of 75-750 nM with a detection limit of 63 nM. These results reveled that GSH capped CIS/ZnS QD sensor could be a potential fluorescent probe for the detection of Cu2+ ions in aqueous solutions.