Paired electrosynthesis of ZnSe/ZnS quantum dots and Cu2+ detection by fluorescence quenching

In this work, ZnSe and ZnSe/ZnS quantum-dots (QDs) stabilized by 3-mercaptopropionic acid (MPA) were synthesized by an electrochemical method, in aqueous medium (pH 7). A paired electrolysis (i = 30 mA) of elemental selenium and zinc rod sacrificial anode was carried out in an electrochemical cavity cell, simultaneously producing Se2- (cathode) and Zn2+ (anode), which reacts in the central compartment of the cell, in a controlled way. Nanoparticles were characterized by UV-vis and fluorescence spectroscopy, XRD, and HRTEM; hydrodynamic diameter and zeta potential were also determined. ZnSe-MPA nanoparticles of 3.2 nm average diameter were obtained with a zinc blend crystal structure and luminescence QY of 4.8%. The same electrochemical procedure was carried out to synthesize ZnS-MPA, which was used in the preparation of core/shell QDs. The ZnSe/ZnS-MPA nanoparticle were prepared with diameter of 4.8 nm, and the luminescence quantum yield was increased to 9.8% due to the decrease on the number of surface defects of the ZnSe core. ZnSe/ZnS-MPA presented efficiency for Cu2+ sensing by fluorescence quenching method, showing good sensitivity with LoD = 0.17 mu mol L-1. A static quenching mechanism was proposed, based on the quenching rate constant (K-q).