Electrodes Electrochemical impedance spectroscopy data   Rs (Ω)   Q (x 106 nF ) Rct (Ω ) Cdl (u F) GCE 54.70 (9.05) 2.77 (1.33) 98.40 (4.63) 163.70 (10.56) GCE-MWCNT 80.40 (0.50) 307.00 (3.25) 8.50 (7.77) 78.50 (15.72) GCE-NiO 62.60 (8.53) 2.65 (1.31) 104.80 (4.72) 152.30 (10.72) GCE-ZnO 81.20 (7.95) 80.30 (3.04) 80.40 (7.47) 180.90 (16.73) GCE-Fe3 O4 134.60 (3.18) 80.30 (3.04) 319.00 (2.586) 8.66 (3.54) GCE-MWCNT-NiO 74.60 (0.57) 350.00 (3.80) 9.50 (7.18) 63.00 (14.82) GCE-MWCNT-ZnO 80.10 (0.49) 332.00 (3.45) 10.48 (6.59) 72.49 (12.74) GCE-MWCNT-Fe3O4 78.90 (0.65) 235.00 (6.64) 33.30 (5.19) 93.30 (5.15)

Table 2: Impedance data obtained electrodes in 1 × 10,-4 M DA solution in pH 7.0 PBS (at 0.2 V vs. Ag/AgCl saturated KCl). The values in parentheses are percent errors of data fitting.