Simple Fluorescence Turn-On Chemosensor for Selective Detection of Ba 2+ Ion and Its Live Cell Imaging.

A phenoxazine-based fluorescence chemosensor 4PB [(4-( tert -butyl)- N -(4-((4-((5-oxo-5 H -benzo[ a ]phenoxazin-6-yl)amino)phenyl)sulfonyl)phenyl)benzamide)] was designed and synthesized by a simple synthetic methods. The 4PB fluorescence chemosensor selectively detects Ba ²⁺ in the existence of other alkaline metal ions. In addition, 4PB showed high selectivity and sensitivity for Ba ²⁺ detection. The detection limit of 4PB was 0.282 μM and the binding constant was 1.0 × 10 ⁶ M ^-1 in CH ₃ CN/H ₂ O (97.5:2.5 v/v, HEPES = 1.25 mM, pH 7.3) medium. This chemosensor functioned through the intramolecular charge transfer (ICT) mechanism, which was further confirmed by DFT studies. Live cell imaging in MCF-7 cells confirmed the cell permeability of 4PB and its capability for specific detection of Ba ²⁺ in living cells.