Carbazole-thiophene based fluorescent probe for selective detection of Cu²⁺ and its live cell imaging

Highly sensitive and specific imaging of copper ion (Cu²⁺) in living cells is essential for better understanding the physiological and metabolic processes. We develop a novel fluorescent probe based on carbazole-thiophene for specific Cu²⁺ detection in living cells. Job's plot and density functional theory (DFT) confirmed a stoichiometric ratio of 2:1 between the probe molecules and Cu²⁺. This probe exhibits strong fluorescence in aqueous media, while its fluorescence intensity significantly decreased in the presence of Cu²⁺. An in vitro assay shows that the fluorescent probe has rapid response within 5 s and high sensitivity for the detection of Cu²⁺ in the range from 1 to 10 μM with a detection limit of 0.29 μM. Live cell studies reveal that the fluorescent probe has good cell-membrane permeability and can successfully visualize the fluctuation of the intracellular Cu²⁺ concentration. In addition, the fluorescent probe has low cytotoxicity, which may provide a new tool for monitoring other analytes in living cells.