l-Cysteine-capped ZnS quantum dots based fluorescence sensor for Cu2+ ion

This paper describes the investigation of surface modified quantum dots (QDs) as a sensing receptor for Cu2+ ion detection by optical approach. Water-soluble l-cysteine-capped ZnS QDs have been synthesised in aqueous medium. These functionalised nanoparticles were used as a fluorescence sensor for Cu (II) ion, involved in the fluorescence quenching. The optimum fluorescence intensity was found to be at pH 5.0 with a nanoparticle concentration of 2.5 mg L−1. The effect of foreign ions on the intensity of ZnS QDs showed a low interference response towards other metal ions except Ag+ and Fe3+ ions. The quenching mechanism was studied and the results show the existence of both static and dynamic quenching processes. However, static quenching is more prominent of the two. The limit of detection of this system was found to be 7.1 × 10−6 M. When compared with single organic fluorophores, l-cysteine-capped ZnS QDs are brighter and more stable against photobleaching. This method is not only simple, sensitive and low cost, but also reliable for practical applications.