Colorimetric and fluorescent “turn-off” benzimidazole-derived sensor for selective detection of Cu2+ ions in real water samples and bio-imaging studies

(E)-2-(((2-(1 H-benzo[d]imidazol-2-yl)phenyl)imino)methyl)-3-bromo-6-methoxyphenol( BBIM ), a novel Schiff base ligand based on benzimidazole, was synthesized and structurally characterized using spectroscopic techniques. The probe BBIM tested as a dual-mode colorimetric and fluorometric sensor for the detection of Cu 2+ ions. BBIM demonstrated strong fluorescence quenching (a “turn-off” response) and a clear color shift from colorless to yellow, together with good selectivity and sensitivity toward Cu 2+ . Further, 1:1 BBIM –Cu 2+ complex was formed, according to Job’s plot analysis. For colorimetric and fluorometric detection, the probe showed detection limits of 0.88 × 10 −6 M and 0.109 × 10⁻ 6 M, respectively. Studies using live-cell imaging in A549 cells showed significant intracellular fluorescence and efficient cellular uptake, which were successfully muted following the addition of Cu 2+ .The experimental sensing behavior was validated by calculations using density functional theory (DFT/TD-DFT). Additionally, BBIM was effectively used to detect Cu 2+ in real water samples and exhibited usefulness using cotton-swab and paper-strip sensing platforms. These findings demonstrate the potential of BBIM as an easy-to-use and efficient sensor for monitoring Cu 2+ in biological and environmental systems.