Research PaperHighly selective and sensitive detection of Hg2+ based on fluorescence enhancement of Mn-doped ZnSe QDs by Hg2+-Mn2+ replacement

- A new turn-on strategy for detecting Hg2+ was developed.
- This strategy shows good selectivity and recognition for Hg2+ detection.
- The limit of detection is 7 nM by fluorescence spectra, which is lower than the mercury toxicity level (10 nM).
- This sensing system has been successfully used for the analysis of real water samples.

The pollution of Hg2+ is one of the most serious problems to human health due to their high toxicity, mobility, difficulty in degradation and ability of accumulation in ecological systems. Thus, it is of great importance to develop highly selective and sensitive probe for detecting Hg2+ in aquatic ecosystems. Here we propose a new turn-on strategy for specific recognition and detection of Hg2+. Mn-doped ZnSe quantum dots (QDs) with small size (2.1 nm) were prepared and adopted as probe, the small size of doped QDs makes the replacement of Mn2+ by Hg2+ accessible, which eliminates the fluorescence quenching effect of superficial Mn2+ on Mn-doped ZnSe QDs. Different from traditional semiconductor nanocrystals based turn-off probe for detecting Hg2+, we realize a turn-on strategy for the selective detection of Hg2+ by Hg2+-Mn2+ replacement using semiconductor nanocrystals (Mn-doped ZnSe QDs). This turn-on mechanism was verified by fluorescence spectra, ICP-AES and XPS. In the absence of Hg2+, Mn-doped ZnSe QDs possessed low fluorescence intensity. With the addition of Hg2+, the fluorescence intensity around 600 nm increased dramatically. Our Mn-doped ZnSe QDs exhibits excellent selectivity and sensitivity for Hg2+. The limit of detection is 7.0 nM, which is lower than the mercury toxic level defined by the U.S. Environmental Protection Agency (10 nM). The result of Hg2+ detection in real samples indicates the feasibility and sensitivity of our probe for application in environmental samples.

The detection of Hg2+ is realized by substituting fluorescence quencher (superficial Mn2+) in Mn-doped ZnSe quantum dots.197