Rhodamine-based chemodosimeter for fluorescent determination of Hg2+ in 100% aqueous solution and in living cells

• A water-soluble rhodamine derivative is used as a chemodosimeter for Hg2+.
• The chemodosimeter exhibits a highly sensitive response with a 42-fold enhancement.
• The chemodosimeter exhibits a high selectivity for Hg2+ over other metal ions.
• The chemodosimeter has been used in water samples and living cells successfully.

A rhodamine spirolactam derivative (1) bearing a hydrophilic carboxylic acid group is developed as a fluorescent chemodosimeter for bivalent mercury ions (Hg2+) in 100% aqueous solution. It exhibits a highly sensitive “turn-on” fluorescent response toward Hg2+ with a 42-fold fluorescence intensity enhancement under 1 equiv. of Hg2+ added. The chemodosimeter can be applied to the quantification of Hg2+ with a linear range covering from 3.0 × 10−7 to 1.0 × 10−5 M and a detection limit of 9.7 × 10−8 M. Most importantly, the fluorescence changes of the chemodosimeter are remarkably specific for Hg2+ in the presence of other metal ions, which meet the selective requirements for practical application. Moreover, the experiment results show that the response behavior of 1 towards Hg2+ is pH independent in neutral condition (pH 5.0–8.0) and the response is fast (response time less than 3 min). Furthermore, the ring-opening mechanism of the rhodamine spirolactam induced by Hg2+ was supported by NMR, MS, and DFT theoretical calculations. In addition, the proposed chemodosimeter has been used to detect Hg2+ in water samples and image Hg2+ in living cells with satisfying results.

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