The composites of cationic polyelectrolyte and glutathione-capped quantum dots for selective fluorescence detection of Cu2+

Abstract

A new composite of poly(diallyldimethylammonium chloride) (PDDAC) and glutathione-capped ZnHgSe quantum dots (GSH-QDs) has been developed for sensing Cu2+ in aqueous solution on the basis of fluorescence quenching. The formation of the composite is dominated through the electrostatic interaction between cationic PDDAC and anionic GSH-QDs. When Cu2+ collides with PDDA/GSH-QDs composites, Cu2+ displaces the Zn and/or Hg in the ZnHgSe QDs and forms extremely low soluble particles of CuSe onto the surface of QDs. As a result, the fluorescence intensity of QDs is quenched efficiently. Compared to GSH-QDs, PDDA/GSH-QDs composites exhibited better selectivity toward Cu2+ as a result of minimizing the electrostatic interaction between metal ions and the ligands. The selectivity of PDDA/GSH-QDs composites toward Cu2+ was further improved by increasing glycine concentration and optimizing the pH of the solution. Under the optimal conditions, PDDA/GSH-QDs composites provided the limits of detection for Cu2+ at a signal-to-noise ratio of 3 of 0.2 nM (∼2.0 ppt). We believe that this probe has great potential for the detection of Cu2+ in environmental waters.