Rhodamine B-based “turn-on” fluorescent and colorimetric chemosensors for highly sensitive and selective detection of mercury (II) ions

► Multidentate sulfide-containing ligand bounded to rhodamine B as new Hg2+ sensor. ► Sensor is prepared by a straightforward two-step synthesis. ► Sensor shows high sensitivity and selectivity to Hg2+ with detection limit of 10 ppb. ► Hg2+-binding is indicated by both fluorescence enhancement and chromogenic change. ► Sensor serves as a naked-eye indicator by color change from colorless to pink.