Selective sensing of Hg²⁺ using rhodamine-thiophene conjugate: red light emission and visual detection of intracellular Hg²⁺ at nanomolar level.

Rhodamine-thiophene conjugate (L) has been synthesized and characterized by (1)H NMR, FTIR and mass spectra. L shows a large enhancement in emission intensity in presence of Hg(2+). Moreover, naked eye color of L becomes intense red in presence of Hg(2+). The lowest detection limit for Hg(2+) is 1 × 10(-9)M in HEPES buffer (0.1M in EtOH/water, 1/1, v/v, pH 7.4). Hg(2+) induced chelation enhanced fluorescence (CHEF) is associated with spirolacram ring opening of the rhodamine unit. Trace level intracellular Hg(2+) is visualized under fluorescence microscope.