Using Smartphone APP To Determine the CN(–) Concentration Quantitatively in Tap Water: Synthesis of the Naked-Eye Colorimetric Chemosensor for CN(–) and Ni(2+) Based on Benzothiazole

[Image: see text] A naked-eye colorimetric chemosensor DK based on benzothiazole could recognize CN(–) effectively. When DK interacted with CN(–) in the aqueous solution, the obvious color change of the solution was directly observed by the naked eye. Other anions did not cause any interference. It is interesting that DK could also discriminate Ni(2+) from other cations, and the possible interaction mode between them was verified based on the Job’s plot, (1)H nuclear magnetic resonance titration, infrared , electrospray ionization mass spectrometry, scanning electron microscopy analysis, and density functional theory calculation methods. As a result, it is clear that the mode of action between DK and CN(–) was different from that between DK and Ni(2+). Meanwhile, the limit of detection of DK toward CN(–) and Ni(2+) was calculated to be 1.7 × 10(–8) or 7.4 × 10(–9) M, respectively. In addition, CN(–) was recognized qualitatively by a test paper and silica gel plates made from DK. DK was able to detect CN(–) in tap water quantitatively, rapidly, and on-site by the use of a smartphone APP. All results implied that DK has certain prospects for practical application to identify CN(–) in water.