Abstract A highly efficient and selective rhodamine B sensor bearing triazole unit (RHT) as the metal ion receptor was designed and synthesized. RHT was characterized by 1H NMR, 13C NMR, APT, COSY, FTIR, elemental analysis, and also its binding selectivity toward various metal ions was studied. Fluorescence enhancement by factors 24 times was achieved upon selective interaction with Hg2+ ion over other metal ions in aqueous solutions. Selective fluorescent enhancement of RHT was attributed to ring opening from the spirolactam (nonfluorescent) to ring-opened amide (fluorescent). Also, distinct color changes from colorless to pink provided "naked eye" detection of Hg2+.