A fluorometric assay was developed for the determination of copper(II) ion based on its quenching effect on the green fluorescent probe of SiO2-anchored CdS nanocrystals (SiO2/CdS NCs). The fluorescent probe was prepared by a surface ion-directing strategy for homogeneous precipitation of CdS NCs onto the carboxyl-capped SiO2 core surfaces. In comparison to CdS NCs, the SiO2/CdS NCs has strong fluorescence emission and good photostability. Moreover, SiO2/CdS NCs show higher fluorescence selectivity for copper(II) ions than for other common metal ions because copper(II) ions have a strong fluorescence quenching effect on SiO2/CdS NCs. At excitation/emission wavelengths of 300/516 nm, the resulting fluorescent probe shows wide linear ranges from 0.01 to 2 μM with a detection limit of 6.3 nM for copper(II) ions. The method has been applied to the determination of trace copper(II) ions in tea infusions with satisfactory results. Graphical abstract.
Keywords: CuS/CdS heterojunction; Electron transfer; Fluorescence quenching; Food analysis; Heavy metal ions; Nanocrystals; Tea sample.