A water-soluble glucose-appended quinoline–benzothiazole conjugate as a selective and sensitive receptor for Cu+ ions in aqueous media and intracellular bio-imaging in live cells†

A water-soluble and biologically benign glucose-appended quinoline–benzothiazole conjugate (L) has been synthesized and characterized using various spectroscopy techniques. The recognition properties of L show selective recognition of Cu⁺ ions among other biological metal ions including Cu²⁺ ions in PBS buffer at pH 7.4. L exhibited a switch-on fluorescence enhancement upon the addition of Cu⁺ with a detection limit of 1.48 × 10⁻⁸ M in an aqueous medium. Job's plot confirmed the 1 : 1 binding ratio observed between probe L and Cu⁺ ions with an association constant (K_a) of 1.46 × 10⁵ M⁻¹. The proposed complex binding mechanism was supported by UV-Vis, fluorescence and ESI-MS. The coordination features of the {L + Cu⁺} complex were delineated using DFT computational calculations. Furthermore, L was successfully applied for intracellular fluorescence bio-imaging of Cu⁺ ions in L929 living cells, suggesting that it holds significant potential for Cu⁺ ion bio-imaging and disease diagnosis.