For UV-Visible and fluorescence measurements, 1.0 x 10 -3 M stock solution of PET-EA was prepared in anhydrous CH3CN and the stock solutions for metal ions were prepared by dissolving their perchlorate salts in deionized water at the concentrations of 1.0 x 10 -3 M. The probe PTE-EA (10 x 10 -6 M) added as volume of 0.03 mL from stock solution to the 2.07 mL of CH3CN and 0.9 mL of HEPES buffer to make up total of 3 mL in the cuvette.