The Nyquist diagrams of the bare GC and the 2-TBI/GC electrodes are shown in Fig. 3. The impedance plot of the bare GC is a straight line (inset of Fig. 3). However, the 2-TBI/GC electrode shows a semicircle at a high frequency region, implying that the electron transfer between 1.0 mM [Fe(CN)6]3 −/4 − and the 2-TBI/GC electrode is blocked. Equivalent circuit comprises the solution resistance (Rs), the charge transfer resistance (Rct) and the constant phase element (CPE) (inset of Fig. 3). R0ct and Rct values were calculated from the impedance plots for 1.0 mM [Fe(CN)6]3 −/4 − at bare GC and the 2-TBI/GC electrodes as 100.0 kΩ and 425.0 kΩ, respectively. The Rct value at the 2-TBI/GC electrode is higher than that at the bare GC electrode, indicating the passivation property of the film.