Ultrasensitive fluorogenic chemosensor based on ESIPT phenomenon for selective determination of Cu2+ ion in aqueous system and its application in environmental samples and biological imaging

A new fluorometric sensor based on salicylideneaniline derivative for the detection of Cu2+ ion in aqueous media was developed and synthesized. The sensor showed strong absorption and fluorescence emission in an aqueous system through ESIPT and ICT characters. The greenish yellow fluorescence emission quenching and color change from bright yellow to pale yellow were observed after complexation with Cu2+ via the chelation-enhanced quenching (CHEQ) process. The sensor can recognize Cu2+ ion with high sensitivity and specificity over potential interfering ions as well as a low detection limit of 0.87 ppb, which was lower than the limit level concentration of Cu2+ in drinking water by the United States Environmental Protection Agency (U.S. EPA) and World Health Organization (WHO). The Job's plot, X-ray Absorption Spectroscopy (XAS), and 1H NMR illustrated the chelating mode between PS and Cu2+ ion in 1:1 stoichiometric complexation. The DFT calculations revealed ligand-to-metal charge transfer (LMCT) phenomena upon the Cu2+ binding of PS. Moreover, this fluorescence sensor was successfully employed for analyzing Cu2+ concentration in real water samples as well as living cells.