The test strips containing 1 were utilized to detect different cations. Test paper sprayed with these cation solutions and dried rapidly, the obvious color change was observed only with Ni2+ ion solution. Also, these test strips were applied for sensing different Ni2+ ion concentrations, exhibiting colorimetric changes differentiable to naked eyes. As depicted in Fig. 4, the red color of the test strips intensified from 0, to 5.0 × 10− 5 M, 1.0 × 10− 4 M, 1.0 × 10− 3 M and shows that the discernible concentration of Ni2+ ion can be as low as 5.0 × 10− 5 M.