Modulating the selectivity by switching sensing media: a bifunctional chemosensor selectivity for Cd2+ and Pb2+ in different aqueous solutions

A novel bifunctional fluorescent probe RI, based on rhodamine with isatin, was designed and synthesized. Switching of the selectivity of RI between various metal ions was achieved by judicious choice of sensing media. RI gives a turn-on fluorometric and colorimetric signal toward Cd2+ in 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) (10 mM, CH3OH–H2O, 4 : 6, v/v, pH 7.6) buffer solution and a turn-on colorimetric signal toward Pb2+ in Tris-HCl (70 mM, CH3OH–H2O, 6 : 4, v/v, pH 7.6) buffer solution. To the best of our knowledge, this is the first example of a chemosensor based on a small molecule that can selectively recognize both Cd2+ and Pb2+ in different sensing systems. Fluorescence imaging of Cd2+ in living cells was also obtained.