Simple Fluorescence Turn-On Chemosensor for Selective Detection of Ba²⁺ Ion and Its Live Cell Imaging

Abstract

A phenoxazine-based fluorescence chemosensor <b>4PB</b> [(4-(<i>tert</i>-butyl)-<i>N</i>-(4-((4-((5-oxo-5<i>H</i>-benzo[<i>a</i>]phenoxazin-6-yl)amino)phenyl)sulfonyl)phenyl)benzamide)] was designed and synthesized by a simple synthetic methods. The <b>4PB</b> fluorescence chemosensor selectively detects Ba²⁺ in the existence of other alkaline metal ions. In addition, <b>4PB</b> showed high selectivity and sensitivity for Ba²⁺ detection. The detection limit of <b>4PB</b> was 0.282 μM and the binding constant was 1.0 × 10⁶ M^-1 in CH₃CN/H₂O (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 <b>4PB</b> and its capability for specific detection of Ba²⁺ in living cells.