The Composites of Cationic Polyelectrolyte and Glutathione‐capped Quantum Dots for Selective Fluorescence Detection of Cu 2+

A new composite of poly(diallyldimethylammonium chloride) (PDDAC) and glutathione‐capped ZnHgSe quantum dots (GSH‐QDs) has been developed for sensing Cu 2+ 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 Cu 2+ collides with PDDA/GSH‐QDs composites, Cu 2+ 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 Cu 2+ as a result of minimizing the electrostatic interaction between metal ions and the ligands. The selectivity of PDDA/GSH‐QDs composites toward Cu 2+ 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 Cu 2+ 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 Cu 2+ in environmental waters.