Picomolar Level Detection of Copper(II) and Mercury(II) Ions Using Dual-Stabilizer-Capped CdTe Quantum Dots

Abstract

In this paper, dual-stabilizer-capped CdTe quantum dots were used as modulated photoluminescence (PL) sensors for the subpicomolar level detection of copper(II) (Cu2+) and mercury(II) (Hg2+) ions in aqueous solution for the first time. The dual-stabilizer-capped CdTe quantum dots were synthesized using mercaptopropionic acid (MPA) and sodium hexametaphosphate (SHMP) as surface-modified ligands via a convenient hydrothermal process. The researches showed a low interference response of the MPA-SHMP-capped CdTe quantum dots towards other metal ions. The highly efficient PL quenching ability in the presence of Hg2+ or Cu2+ ions due to the formed nonfluorescent metal complexes via robust Hg2+–O interaction with the carboxy oxygen elements of surface ligands of MPA, and on the basis of the competitive binding of the mercapto groups of the MPA between the CdTe quantum dots and the Cu2+ ions, respectively, which allowed the analysis of Hg2+ or Cu2+ ions down to the picomolar levels. Under optimal conditions, the response of the MPA-SHMP-capped CdTe quantum dot PL intensity is linearly proportional to the Cu2+ and Hg2+ ion concentration ranging from 0.1 to 1000 and 0.3 to 1000 nM with a detection limit of 41.6 and 97.0 pM, respectively. The diagnostic capability and potential in practical applications of this method have been demonstrated by detecting Cu2+ and Hg2+ ions in environmental water samples.