Turn-on fluorescent chemosensor for Hg²⁺ based on multivalent rhodamine ligands.

Rhodamine-based fluorescent chemosensors 1 and 2 exhibit selective fluorescence enhancement to Fe3+ and Hg2+ over other metal ions at 580 nm in CH(3)CN/H(2)O (3/1, v/v) solution. Bis(rhodamine) chemosensor 1, under optimized conditions (CH(3)CN/HEPES buffer (0.02 M, pH = 7.0) (95/5, v/v)), shows a high selectivity and sensitivity to Hg2+, with a linear working range of 0-50 μM, a wide pH span of 4-10, and a detection limit of 0.4 μM Hg2+.