A highly sensitive protocol for the determination of Hg2+ in environmental water using time-gated mode

• Described a sensing strategy for Hg2+ detection using time-gated mode.
• Employing long lifetime fluorescence Mn:CdS/ZnS QDs to reduce the background signals.
• Employing Mn:CdS/ZnS QDs and GO as the energy transfer pairs.
• Displays the advantages of high sensitivity (LOD: 0.11 nM) and excellent selectivity.
• Applied successfully to the determination of Hg2+ in environmental water samples.

In this paper, a sensitive time-gated fluorescent sensing strategy for mercury ions (Hg2+) monitoring is developed based on Hg2+-mediated thymine (T)–Hg2+–T structure and the mechanism of fluorescence resonance energy transfer from Mn-doped CdS/ZnS quantum dots to graphene oxide. The authors employ two T-rich single-stranded DNA (ssDNA) as the capture probes for Hg2+, and one of them is modified with Mn-doped CdS/ZnS quantum dots. The addition of Hg2+ makes the two T-rich ssDNA hybrids with each other to form stable T-Hg2+-T coordination chemistry, which makes Mn-doped CdS/ZnS quantum dots far away from the surface of graphene oxide. As a result, the fluorescence signal is increased obviously compared with that without Hg2+. The time-gated fluorescence intensities are linear with the concentrations of Hg2+ in the range from 0.20 to 10 nM with a limit of detection of 0.11 nM. The detection limit is much lower than the U.S. Environmental Protection Agency limit of the concentration of Hg2+ for drinking water. The time-gated fluorescent sensing strategy is specific for Hg2+ even with interference by other metal ions based on the results of selectivity experiments. Importantly, the proposed sensing strategy is applied successfully to the determination of Hg2+ in environmental water samples.

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