Cadmium sulfide quantum dots modified by chitosan as fluorescence probe for copper (II) ion determination

CdS quantum dots (QDs) have been prepared and modified with chitosan. Based on the quenching of fluorescence signals of the functionalized CdS QDs at 531 nm wavelength and enhancement of signals the 400–700 nm wavelength range by Cu²⁺ at pH 4.2, a simple, rapid and specific method for Cu²⁺ determination is presented. Under optimum conditions, the relative fluorescence intensity of CdS QDs is linearly proportional to copper concentration from 8.0 nmol L^?1 to 3.0 μmol L^?1 with a detection limit of 1.2 nmol L^?1. The mechanism can be explained in terms of strong binding of Cu²⁺ onto the surface of CdS, resulting in a chemical displacement of Cd²⁺ ions and the formation of CuS on the surface of the QDs.