Cu2+-modulated cysteamine-capped CdS quantum dots as a turn-on fluorescence sensor for cyanide recognition

A new fluorescence sensor for detection of cyanide ions (CN−) in aqueous media based on the recovered fluorescence of cysteamine capped CdS quantum dots [Cys-CdS QDs]-Cu2+ system was proposed. The fluorescence intensity of Cys-CdS QDs was quenched by Cu2+ due to the binding of Cu2+ to cysteamine on the surface of the QDs. The degree of fluorescence quenching was proportional to the concentration of Cu2+. However, in the presence of CN−, the fluorescence intensity of Cys-CdS QDs was found to be efficiently recovered. Experimental results showed that the pH of the buffer solution and the concentration of Cu2+ affected the fluorescence intensity upon adding CN−. Under the optimal condition, the recovered fluorescence intensity was linearly proportional to the increasing CN− concentration in the range 2.5–20 μM. The limit of detection and the limit of quantification were found to be 1.13 μM and 3.23 μM, respectively. In addition, among the tested ions, only CN− could turn on the fluorescence intensity suggesting that the [Cys-CdS QDs]-Cu2+ system was a highly selective sensor for CN−. Moreover, this proposed sensor was demonstrated to detect CN− in drinking water with satisfactory results.