Rhodamine-thiophene conjugate (L) has been synthesized and characterized by H-1 NMR, FTIR and mass spectra. L shows a large enhancement in emission intensity in presence of Hg2+. Moreover, naked eye color of L becomes intense red in presence of Hg2+. The lowest detection limit for Hg2+ is 1 x 10(-9) M in HEPES buffer (0.1 M in EtOH/water, 1/1, v/v, pH 7.4). Hg2+ induced chelation enhanced fluorescence (CHEF) is associated with spirolacram ring opening of the rhodamine unit. Trace level intracellular Hg2+ is visualized under fluorescence microscope. (C) 2013 Elsevier B.V. All rights reserved.