Novel application of the chitosan-capped ZnS:Mn nanocrystals for the detection of copper (II) ions in aqueous solution

Orange-light-emitting ZnS:Mn nanocrystals (NCs) were prepared by capping their surface with chitosan (Chit) molecules in water. The characterization works for the freshly prepared colloidal NCs were performed using various spectroscopic methods. The optical properties of the NCs were thoroughly investigated using UV–Visible absorption and solution photoluminescence (PL) spectroscopy. The solution PL spectrum for the ZnS:Mn-Chit NCs showed a broad emission peak around at 597 nm. The HR-TEM image showed that the average particle size of the isolated solid NCs was 7.5 nm, which were also accorded to Debye–Scherrer calculations using the data obtained by XRD analysis. The surface charge of the ZnS:Mn-Chit NCs was measured as − 33.4 mV, and they formed fairly huge aggregates with the average particle size of 385 nm in water. In this study, the negatively charged ZnS:Mn-Chit NCs were applied as photosensors in the detection of specific divalent transition metal cations. Consequently, the NCs showed exclusive fluorescence quenching effects upon the addition of Cu (II) metal ions, which suggested that the ZnS:Mn-Chit NCs can be an efficient photosensor in the detection of copper ions which are very important in a biological system. In addition, the ZnS:Mn-Chit NCs have never been applied as a metal ion sensor in water.