Label-free and reversible immunosensor based upon an ac impedance interrogation protocol

We report the fabrication of a label-free and reagentless immunosensor based on the direct incorporation of antibodies into conducting polymer films along with a subsequent ac impedimetric electrochemical interrogation. Model sensors of this type were prepared by electrochemically polymerising conducting polypyrrole films containing anti-BSA at the surface of screen-printed carbon electrodes. Films containing chloride or anti-human IgG as counter-ions were used as controls. An ac measurement protocol was used to determine the impedance of the electrodes when immersed in water or analyte solutions. A selective and reversible binding of analyte to the electrode could be monitored electrochemically and studies are reported in detail relating analyte concentrations to bulk impedimetric measurements, the real component, the imaginary component and the phase angle of the responses. The results of this study showed detectable and reversible antibody-antigen interactions could be measured and mainly affected the Faradaic behaviour of the electrode. BSA could be detected with a linear response from 0 to 75 ppm.