Colorimetric and fluorescent probes for real-time naked eye sensing of copper ion in solution and on paper substrate

In this paper, BT ((E)-2-(4-(4-(bis(pyridin-2-ylmethyl)amino)styryl)-3-cyano-5,5-dimethylfuran-2(5H)-ylidene)malononitrile) with strong donor-π-acceptor structure was synthesized, which showed both colorimetric and fluorescent sensing ability to Cu2+ with high selectivity and sensitivity. The job plot and mass spectra measurement revealed a 1 : 1 coordination mode between Cu2+ and probe BT in ethanol/HEPES buffer (pH 7.2, v/v, 1/4) solution, and the binding constant was calculated to be 3.6×104 M–1. The color of BT solution (10 μM) immediately turned from purple red to yellow and the red fluorescence was quenched obviously when certain amount of Cu2+ was added, which enabled a dual-channel detection of Cu2+. A paper strip pre-stained with BT solution was further fabricated and it also showed excellent sensing ability toward Cu2+ with a detection limit as low as 10-6 M with naked-eye, which give better portability and operation simplicity that is favorable for on-site analysis of Cu2+ in...