A selective chromone-based colorimetric chemosensor for detecting Cu2+ in near-perfect aqueous solution and test kit

A colorimetric chemosensor CMF (N '-[(E)-(4-oxo-4H-chromen-3-yl)methylidene]furan-2-carbohydrazide) was applied for detecting Cu2+. CMF showed colorimetric selectivity to Cu2+ through a color variation from colorless to yellow. Binding ratio between CMF and Cu2+ was analyzed by Job plot to be a 2:1. Limit of detection was found to be 0.38 mu M. The practicality of CMF was illustrated by the quantification of Cu2+ in real samples. In particular, the CMF-coated test kit was able to detect the copper ions at a concentration lower than the recommended concentration (31.5 mu M) of the World Health Organization (WHO) for copper ion. The binding mode of CMF and copper ions was studied through UV-visible spectroscopy, H-1 NMR titration, ESI-mass analysis, and DFT calculations. Sensing mechanism of CMF to Cu2+ was proposed to be the ligand-to-metal charge transfer (LMCT) through DFT calculations.