Sequential detection of Cu 2+ and cysteine using an imidazole‐based chemosensor in aqueous solution

A highly substituted imidazole‐based colorimetric and fluorogenic chemosensor, 2‐methoxy‐4‐(4,5‐diphenyl‐1H‐imidazol‐2‐yl)phenol (L), for the detection of Cu 2+ ion and subsequent colorimetric detection of an amino acid, cysteine, was investigated. L exhibited a distinct color change from colorless to red in the presence of Cu 2+ in an aqueous medium. The L‐Cu 2+ complex can also be used to detect cysteine by the naked eye over a series of amino acids. The receptor L behaves as a highly selective colorimetric and fluorescent sensor for Cu 2+ ions at concentrations as low as 4.33 and 2.25 μM, respectively. These values are much less compared to the WHO recommended limit of 30 μM for Cu 2+ in drinking water. From Job's plot and the ESI‐MS spectrum, a 1:1 stoichiometric complex between L and Cu 2+ ions can readily be reckoned. This binding was also substantiated by the EPR spectrum and magnetic susceptibility measurements. Additionally, the binding of L with Cu 2+ ions was also manifested in the detection of B16F10 cells. This was substantiated through fluorescence microscopy. The spectrum of the L‐Cu 2+ entity was also attempted to reproduce theoretically. The probable structure of this was also propounded through Density Functional Theory.