A cathodic “signal-on” photoelectrochemical sensor for Hg2+ detection based on ion-exchange with ZnS quantum dots

Abstract A cathodic “signal-on” method was developed for the photoelectrochemical detection of Hg 2+ ions. Here, ZnS quantum dots (QDs) capped with mercaptoacetic acid was assembled on the surface of an indium tin oxide (ITO) electrode through electrostatic interaction between poly dimethyl diallyl ammonium chloride (PDDA) and the ZnS QDs. HgS was formed on the ZnS surface by ion-exchange in the presence of Hg 2+ ions in solution. The cathodic photocurrent increased under visible light irradiation with a light-emitting diode lamp. This novel strategy exhibits high sensitivity and good selectivity owing to the low background signal and the benefits of ion-exchange technology. The cathodic photocurrent increases linearly with Hg 2+ concentration in the range 1 × 10 −11 –1 × 10 −6  M, providing a detection limit of 2 pM (S/N = 3). This sensor provides a promising new strategy for the detection of trace heavy metal ions.