A fully-aqueous red-fluorescent probe for selective optical sensing of Hg2+ and its application in living cells

• A water soluble and reversible Hg2+ ion sensor probe is synthesized.
• This probe works as a colorimetric and naked-eye sensor towards Hg2+ ion.
• A large blue shift is observed in absorption of the probe coordinated with Hg2+.
• This probe has the optical sensor potential to be used in living cell applications.

A new red-fluorescent mercury ion sensor material is designed and synthesized, which is composed of a tweezer-shaped hydrophilic probe containing bifurcated soft-base atoms N and S coupled with 2-dicyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran (TCF) unit. By virtue of the strong electron-accepting nature of TCF unit (as a push–pull chromophore), this designed sensor material can selectively detect Hg2+ over various tested metal ions in a 100% aqueous medium via naked-eye and photoluminescence (PL) observations. Theoretical and time-resolved photoluminescence measurements further confirmed the selectivity and reversibility of the probe towards Hg2+ via intramolocular charge transfer mechanism in this sensor material. Moreover, the living cell tests by confocal fluorescence images of this sensor material towards Hg2+ were also investigated. Finally, distinguished absorption changes and fluorescence quenching spectral appearances allowed us to present the selective optical indicator of Hg2+ via TCF moiety for the first time.

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