Colorimetric recognition of Cu2+ and fluorescent detection of Hg2+ in aqueous media by a dual chemosensor derived from rhodamine B dye with a NS2 receptor

A rhodamine B derivative bearing a NS2-containing receptor (L) is developed as a dual chemosensor for detection of Cu2+ and Hg2+ in aqueous media. L shows highly sensitive colorimetric response to Cu2+ and selectively turn-on fluorescent response to Hg2+ with very low detection limits of 1.63 and 2.36 μM, respectively. The significant absorption enhancement (251-fold) accompanied with a visual color change from colorless to purple upon interaction with Cu2+, making L a suitable “bare-eye” indicator for Cu2+. By means of Job's plot, 1H NMR titration and ESI-MS studies, both 1:1 binding modes (L/Cu2+ and L/Hg2+) are confirmed and a possible sensing mechanism is further proposed. The response behaviours of L toward Cu2+ and Hg2+ are pH independent in a wide range (pH 4.0-9.0). Proof-of-concept experiment demonstrates the potential application of L for trace Cu2+ and Hg2+ detection in complicated environmental water samples. More importantly, the turn-on fluorescent chemosensor L with good membrane-permeable property is successfully applied to microscopic imaging for the detection of Hg2+ in PC3 cells.