A highly selective and sensitive probe, DAC-Hg, has been designed and synthesized for the naked-eye detection of Hg2+ in practical applications. DAC-Hg showed applicative “turn-off” sensing for Hg2+ over other ions. The detection limit was determined to be 5.0 nM, the same as the strictest standard of Hg2+ measurements. A naked-eye evaluation with test strips demonstrated the potential of DAC-Hg for conveniently handled in-situ detection. The application of this established method for analyzing environmental and seafood samples supplied satisfactory results. Therefore, DAC-Hg offered a promising approach for Hg2+ detection as well as hints for sensing other heavy and transition metal ions.