Electrochemical impedance spectroscopy (EIS) data of 5.0 mM [Fe(CN)6] 3−/4− in 0.1 M KCl at a BCPE, b ZnO NPs−CPE, c Poly(glutamic acid)/CP and d Poly(glutamic acid)/ZnO−CPE at a frequency range of 0.01 Hz – 100 kHz, applied potential of 0.15 V and amplitude of 0.005 V

EIS is a very useful technique that indicates the interfacial electron transfer rate. This EIS Data was obtained using CHI 760D Electrochemical Workstation. It was described in the Nyquist plot of 5.0 mM [Fe(CN)6] 3−/4− in 0.1 M KCl at a BCPE, b ZnO NPs−CPE, c Poly(glutamic acid)/CPE ,and d Poly(glutamic acid)/ZnO−CPE at a frequency range of 0.01 Hz – 100 kHz, applied potential of 0.15 V and amplitude of 0.005 V.