Colorimetric and “turn-on” fluorescent determination of Cu2+ ions based on rhodamine–quinoline derivative

A novel rhodamine–quinoline derivative-based indicator for Cu2+ ion determination was designed and synthesized. It exhibited highly selective and sensitive colorimetric and “turn-on” fluorescent responses toward Cu2+ ions based on the ring-opening mechanism of the rhodamine spirolactam in aqueous solution. The colorimetric and fluorescent responses were recorded using a domestic scanner and camera-based home-made fluorescent imaging unit, separately. The images were digitized, and the red (R), green (G), and blue (B) values were investigated. Both colorimetric and fluorescent methods showed good selectivity, and the color/fluorescence changes were remarkable for the Cu2+ ion detection even in the presence of other metal ions. The good linear relationship was easily obtained between the color/fluorescence changes and the concentrations in the range of 20–120 μM.