A novel highly selective colorimetric sensor for Ni(II) ion using coumarin derivatives

A new coumarin based colorimetric nickel sensor 1 with high selectivity and sensitivity toward Ni2+ ion was reported. The absorption maximum of 1 shows a large red shift from 341 nm to 540 nm (Δ = 200 nm) in the presence of Ni2+ ion, and the resulted color change from colorless to pink upon addition of Ni2+ is very easily observed by the naked eye, while other metal ions, such as Zn2+, Cd2+, Cu2+, Fe3+, Ag+, Pb2+, alkali metal and alkaline earth metal cations do not induce such a change. By the “naked eye”, the detection limit of Ni2+ is as low as 0.5 μM in solution, which is lower than the current American Environmental Protection Agency (EPA) standard for drinking water. As far as we are aware of, this is the first reported colorimetric chemosensor capable of detecting Ni2+ ion.