Effect of electrical conditions on an impedimetric immunosensor based on a modified conducting polypyrrole

This work has explored the development of impedimetric immunosensors based on a conducting co-polypyrrole film to which a histidine tag antibody has been bound using a complex NTA chelator coordinated with copper as metal. The electrical properties of the copolymer film have been characterized by electrochemical impedance spectroscopy (EIS). The experimental study of EIS was performed over a range of dc voltages from 0 V to −1.4 V (vs. saturated calomel electrode SCE) where the polypyrrole layers transit from their conducting to insulating state and to demonstrate the contribution of the copper complex as redox probe. The electrical behavior of the biomaterial at these various potentials was studied according to an equivalent circuit fitting the experimental parameters. The results indicated that better immunosensor characteristics were obtained at an applied potential of −1400 mV where the reduction of copper occurs. The impedance obtained at this potential shows a linear variation of charge transfer resistance (Rct) with the specific antigen concentration in the range of 0.1–10 ng mL−1 with a detection limit of 0.1 ng mL−1. Moreover, this study demonstrates that these immunosensors exhibit high sensitivity, stability and reproducibility.