Phenothiazine-rhodamine-based colorimetric and fluorogenic 'turn-on' sensor for Zn and bioimaging studies in live cells.

A phenothiazine-rhodamine (PTRH) fluorescent dyad was synthesized and its ability to selectively sense Zn ions in solution and in in vitro cell lines was tested using various techniques. When compared with other competing metal ions, the PTRH probe showed the high selectivity for Zn ions that was supported by electronic and emission spectral analyses. The emission band at 528 nm for the PTRH probe indicated the ring closed form of PTRH, as for Zn ion binding to PTRH, the λ get shift to 608 nm was accompanied by a pale yellow to pink colour (under visible light) and green to pinkish red fluorescence emission (under UV light) due to ring opening of the spirolactam moiety in the PTRH ligand. Spectral overlap of the donor emission band and the absorption band of the ring opened form of the acceptor moiety contributed towards the fluorescence resonance energy transfer ON mechanism for Zn ion detection. The PTRH sensor had the lowest detection limit for Zn , found to be 2.89 × 10  M. The sensor also demonstrated good sensing application with minimum toxicity for in vitro analyses using HeLa cells.