Rhodamine based “turn–on” molecular switch FRET–sensor for cadmium and sulfide ions and live cell imaging study

Abstract A novel fluorescent chemosensor based on a rhodamine derivative (RBD4) was designed, synthesized, and used as a selective Cd2+ ion sensor. The structure of the fluorescence sensor (RBD4) is confirmed through single crystal X-ray study. On the basis of the Forster resonance energy transfer mechanism between rhodamine and pyridine conjugated dyad, a new colorimetric as well as fluorescence probe was synthesized for the selective detection of Cd2+. This sensor shows high selectivity towards Cd2+ ions in the presence of other competing metal ions. On the basis of thorough experimental and theoretical findings, the additions of Cd2+ ions to the solution of RBD4 helps to generate a new fluorescence peak at 590 nm due to the selective binding of Cd2+ ions with RBD4 in a 1: 1 ratio with a binding constant (K) of 4.2524 × 104 M−1. The detection limit of RBD4 for Cd2+ was 1.025 × 10−8 M, which presented a pronounced sensitivity towards Cd2+. The in situ generated RBD4–Cd2+ complex is able to selectively sense S2− over other anions based on the displacement approach, given a remarkable recovery of fluorescence and UV–vis absorption spectra. The fluorescence sensor has also exhibited very good results in HeLa Cells imaging under physiological pH.