Construction of a Quinoline-based Sequential Functioning Chromogenic Sensor for Copper(II) Ion and Biothiols: Its Application to Test Strips

A new compound BQ ((1E,1'E)-N,N'-((1,3-phenylenebis(oxy))bis(3,1-phenylene))bis(1-(quinolin-2-yl)methanimine)) containing quinoline moiety has been developed as a sequential functioning chromogenic sensor for copper(II) ion and biological thiols (GSH, Cys, and Hcy). BQ had a clear chromogenic response toward only copper ion with a red-shifted absorption. Detection limit for copper(II) ion was calculated to be 1.20 μM. Its application was successfully conducted in test strips. The resultant BQ-Cu²⁺ complex could detect the biological thiols, showing the color change and blue-shifted absorption via the demetallation of copper(II) ion. The possible binding mechanisms of BQ to copper(II) ion and of BQ-Cu²⁺ to biological thiols were understood by UV–vis titrations, Job plot, ESI-MS, and ¹H NMR titrations.