Ion-mediated self-assembly of Cys-capped quantum dots for fluorescence detection of As(iii) in water

A sensitive As(iii) ion detection method has been developed based on ion-mediated self-assembly of cysteine (Cys)-capped quantum dots (QDs), and fluorescence self-quenching. A variety of Cys-capped core/shell CdTe/CdS QDs were prepared via hydrothermal methods. Based on the coordination binding between the As(iii) ion and cystine groups anchored on the QDs, addition of As(iii) ions led to self-assembly of the Cys-capped QDs, which was accompanied by fluorescence self-quenching. The fluorescence response was attributed to the exciton energy transfer of the QD aggregates. The ion-mediated fluorescence quenching was further exploited for quantitative determination of As(iii) ions in water. A limit of detection (LOD) of 10 ng L^-1 (3σ method) and a linear range from 14 to 70 ng L^-1 were obtained for the sensing of As(iii) ions. The system was evaluated using a series of interference targets, and demonstrated high selectivity after addition of mask agents. Finally, the proposed method was successfully employed for the detection of As(iii) in a real water sample. The method was sensitive and specific, and shows great promise in quantitative determination of heavy metal ions in lakes and rivers.