An “off–on” optical sensor for mercury ion detection in aqueous solution and living cells

Abstract A rhodamine-based optical sensor Rh–3S has been developed for selective detection of Hg 2+ in aqueous solution as well as in living cells. UV–vis and fluorescence spectroscopic studies reveal that Rh–3S shows marked sensitivity and selectivity to Hg 2+ with a chelation-induced “off–on” response in acetonitrile (ACN)/MOPS buffer (10 mM, pH 7.3, v/v, 1:1). The Rh–3S sensor binds Hg 2+ in a 1:1 stoichiometry with an apparent binding constant 3.71 × 10 6  M − 1 (log K = 6.57) and displays a distinct change in color and fluorescence upon the alteration of free Hg 2+ levels in solution with a reversible response and little interference with other biological relevant metal ions. Live cell confocal imaging studies demonstrate that the sensor is also capable of imaging the presence of Hg 2+ ions as well as its dynamic changes in live cells.