Figure 4: Impedance spectra of the electrodes of immunosensors A and B exposed to difference concentrations of α-hCG. The impedance results were obtained in the solution containing 0.1M KCl and 5μM K3[Fe(CN)6]/K4[Fe(CN)6] at OCP and frequency range is from 100 kHz to 50 mHz with an Ac probe amplitude of 10mV.