A highly sensitive coumarin-based fluorescent probe for visual detection of Cu2+ in aqueous solution and its bioimaging in living cells

In this work, a highly sensitive fluorescent probe methyl (E)-2-((7-(diethylamino)-2-oxo-2H-chromen-3-yl)methylene)hydrazine-1-carboxylate (SJL) was synthesized from 7-(diethylamino)-2-oxo-2H-chromene-3-carbaldehyde and methyl hydrazinecarboxylate and characterized by various spectroscopic techniques. Highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies of SJL and SJL-Cu2+ complexes were estimated by DFT calculations, thus elucidating the conformation of the complexes. The probe SJL formed a stable complex and displayed a remarkable fluorescence quenching response to Cu2+ with a quenching efficiency of approximately 82.3% in aqueous solution. The binding stoichiometry of SJL-Cu2+ was determined to be 1: 1 based on the Job's plot method, and it exhibited a good linear relationship at ultra-low concentrations with a detection limit of 0.6 μM. The optimum pH range for SJL was 5–9. SJL could be made into test strips for the characterization of Cu2+. In particular, the probe has been used to visualize copper ions in Hela cells and glassfish larvae.