Determination of trace amount of Cu2+ with a multi-responsive colorimetric and reversible chemosensor

A multi-responsive sensor 1 was constructed by combining a ferrocene unit and a rhodamine block via a carbohydrazone bond. The sensor showed high selectivity toward Cu2+ over other common metal ions in a wide pH range with excellent reversibility and rapid response. The obvious color change from colorless to pink upon the addition of Cu2+ could make it a suitable 'naked-eye' indicator for Cu2+. The detection limit (LOD) obtained was down to 2.0 nM and the association constant (K-a) was evaluated as 4.65 x 10(7) M-1. The accuracy for detecting Cu2+ in environmental river water was compared favorably with the traditional atomic absorption spectroscopy method (AAS). Finally, we proposed a reversible ring-opening mechanism (Off-On) of the rhodamine spirolactam induced by Cu2+ binding and a 2 : 1 stoichiometric structure between 1 and Cu2+.