Selective turn-on fluorescence sensor for Ag+ using cysteamine capped CdS quantum dots: Determination of free Ag+ in silver nanoparticles solution

Cadmium sulfide quantum dots capped with cysteamine (Cys–CdS QDs) were demonstrated as a selective fluorescence probe for sensing of free trace silver ions. The fluorescence intensity of the Cys–CdS QDs can be enhanced only in the presence of free Ag+ and the fluorescence spectrum was slightly red shift from the original spectra. In addition, the fluorescence intensities were linearly increased upon increasing Ag+ concentration. At the optimized condition for Ag+ detection, when adding other metal ions to the Cys–CdS QDs solution, fluorescence spectra of Cys–CdS QDs did not change significantly revealing good selectivity of the sensors towards Ag+. The working linear concentration range was found to be 0.1–1.5 µM with LOD of 68 nM. The proposed sensor was then applied to detect free Ag+ in the silver nanoparticles solution. The results showed that the proposed sensor can be efficiently used with good accuracy and precision providing the simple method for detection of free Ag+ in silver nanoparticles of quality control products.