Selective and dual naked eye detection of Cu2+ and Hg2+ ions using a simple quinoline–carbaldehyde chemosensor

• This manuscript describes a highly selective and sensitive chemosensor based on quinoline–carbaldehyde system for Cu2+ and Hg2+ ions.
• This system shows well-defined distinguishable naked-eye visible color changes upon interaction with Cu2+ and Hg2+ ions.
• The lowest detection limit (LOD) of 25 ppb for Cu2+ and 360 ppb for Hg2+ was achieved.
• The diethylamino group present in this system acts as the selective binding site for Cu2+ ions and while the aldehyde and ring nitrogen functionalities for Hg2+ ions.
• A simple and novel dip-stick device has been developed based on this system for the easy and visual analysis of Cu2+ and Hg2+ ions in the aqueous medium.

A new colorimetric chemosensor based on diethylaminoquinolinecarbaldehyde (AQC) was designed and its sensing behavior towards various metal ions has been investigated through photophysical, IR and NMR techniques. Interestingly, this probe can selectively detect both Cu2+ and Hg2+ ions with an easy, well defined naked-eye visible color changes from yellow to colorless and pink, respectively. The uniqueness of this system is that it forms stable 1:1 stoichiometric complexes involving diethylamino moiety for the selective recognition of Cu2+ ions with a detection limit of 25 ppb. For the selective recognition of Hg2+ ions, it forms a 2:1 stoichiometric complex involving quinoline nitrogen and aldehyde functionality and shows a detection limit of 360 ppb. The association constants for both Cu2+ and Hg2+ complexes were determined and are found to be ca. 2.1 ± 0.1 × 104 M−1 and 1.29 ± 0.2 × 108 M−2, respectively. Uniquely, this probe can be coated on a glass surface to fabricate a simple solid-state dipstick device that can be used for the easy visual detection and analysis of Cu2+ and Hg2+ ions in the aqueous medium.

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