Chalcone-Based Colorimetric Chemosensor for Detecting Ni²⁺

The first chalcone-based colorimetric chemosensor DPP (sodium (E)-2,4-dichloro-6-(3-oxo-3-(pyridine-2-yl)prop-1-en-1-yl)phenolate) was synthesized for detecting Ni²⁺ in near-perfect water. The synthesis of DPP was validated by using¹H,¹³C NMR and ESI-MS. DPP selectively sensed Ni²⁺ through the color variation from yellow to purple. Detection limit of DPP for Ni²⁺ was calculated to be 0.36 µM (3σ/slope), which is below the standard (1.2 µM) set by the United States Environmental Protection Agency (EPA).The binding ratio of DPP to Ni²⁺ was determined as a 1:1 by using a Job plot and ESI-mass. The association constant of DPP and Ni²⁺ was calculated as 1.06 × 10⁴ M⁻¹ by the non-linear fitting analysis. In real samples, the sensing application of DPP for Ni²⁺ was successfully performed. DPP-coated paper-supported strips could also be used for detecting Ni²⁺. The binding mechanism of DPP to Ni²⁺ was proposed by ESI-MS, Job plot, UV-vis, FT-IR spectroscopy, and DFT calculations.