“…The pretreatment process modifies the electrode surfaces with specific functions such as carbonyl, carboxyl, and hydroxyl groups. The pretreated GC electrode was washed with double‐distilled water, and then, activated for at least 1.5 h in 0.1 M PBS, pH 5.5, containing 0.002 M EDC and 0.005 M NHS 23, 25. The activated GC electrode was rinsed with the same PBS and immediately placed into 1.0 mM 5Aphen aqueous solution at room temperature for 2 h to form GC‐5Aphen electrode, removed from the 5Aphen solution, rinsed with copiously of water to eliminate physically adsorbed 5Aphen, and, then, immersed in a Fe(II) solution at pH 5.0 to form GC‐5Aphen‐Fe(II) electrode.…”