A new coumarin based colorimetric nickel sensor 1 with high selectivity and sensitivity toward Ni2+ ion was reported. The absor ption 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 μ M 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 chemosen-sor capable of detecting Ni2+ ion.
