Development of highly selective and sensitive fluorimetric label-free mercury aptasensor based on cysteamine@CdTe/ZnS quantum dots, Experimental and theoretical investigation

B. Rezaei, M. Shahshahanipour, Ali A. Ensafi, H. Farrokhpour,

In this paper, an ultra-sensitive and highly selective label-free fluorescent aptasensor was developed for the rapid detection of Hg(II), using water soluble cysteamine-capped CdTe/ZnS quantum dots (cysteamine@CdTe/ZnS QDs) as an luminescent probe and a single strain DNA aptamer designed to specifically bind to Hg(II) ions. Negative charge aptamers could aggregate the cationic cysteamine@CdTe/ZnS core/shell quantum dots, so the fluorescence quenching occurred. When Hg(II) ions, as a target, were added to the quantum dots solution, the aptamers with thymine (T)-rich sequences were selectively bound to the mercury ions due to the powerful affinity of Hg(II) ions to the T bases of the DNA aptamer, leading to the formation of an Hg (II)-bridged T base pair and the aptamers rearrangement into a hairpin-like structure. In the presence of Hg(II), de-aggregation of the quantum dots was occurs, so the fluorescence intensity was gradually increased with enhancing its concentration.  Hg(II) could be measured in the range of  5.0 × 10^-10 to 1.0 × 10^-6 mol L^-1 with a low limit of detection, 8.0 × 10^-11 mol L^-1. The fabricated fluorescent aptasensor also demonstrated excellent selectivity for Hg(II) detection, so it was applied lucratively for the determination of Hg(II) in real water and waste water samples.

Keywords: Mercury ions; CdTe/ZnS core/shell quantum dots; Aptasensor; Fluorescence method.