Using both techniques you can retrieve information regarding the interaction of Ag-Ab. Using the ferri/ferro redox probe allows you to obtain results regarding the aforementioned interaction, because the diffusion coefficient of the redox couple changes due to changes in the double layer formation at the electrode-electrolyte interface. In CV ΔΕp changes are observed while in EIS Rct changes cab be contributed to these changes. Commonly, we use this when we are developing faradic impedimetric sensors. On the other hand, using PBS you can retrieve similar information but from the view of the capacitance and the overall impedance changes due to the Ag-Ab interaction carried out into the electrode surface.

For CV analysis, if you are using the FE(CN)6 3-/4- you are getting a redox pair for which changes due to Ab-Ag interactions are easy to track, while using only the PBS solution, these changes are not so obvious. Similar, for EIS analysis, if you are using only PBS, the Ag-Ab interaction may not induce big chages in the capacitance or the overall impedance; meanwhile, you have higher chances to see a change in the Rct of the FE(CN)6 3-/4- . The question is to see if you could develop a capacitance or a faradaic sensor.

CV and EIS both are complementary electroanalytical tests to analyse the electrochemical double layer on the electrodes. In CV we are scanning the dc potential from a starting value to an end value, in that interval some faradaic reactions of our interest happens, and revert back the scan to the initial potential. in this process measuring the faradaic response generated (current). In EIS we are applying different ac frequencies with a specific amplitude superimposed over the equilibrium dc potential. The impedance change in the double layer is measured. The resistance in the double layer is named impedance since there is capacitive and inductive components (which are frequency dependant resisstance terms, pls refer Randles equivalent circuit and ELECTROCHEMICAL

METHODS Fundamentals and Applications by Allen J Bard, Chapter 10). We are using ferricyanide system since it is one of the best redox species which could study on an electrode. The redox peaks will give clear indication of the double layer changes on the electrode surfaces. Thus when we are incorporating antigens or antibodies over an electrode the double layer changes, this can affect the double layer capacitance and the electron transfer resistance . Thus by monitoring the charge transfer resistance (Rct or Ret) we could understand the charge transfer properties of the double layer. For example if the Rct is high the electron transport between ferricyanide in the solution and the electroode surface is high, this will indicated by the CV recorded in the system by a reduction in peak currents or a shift in potential, because the kinetics is low. Thus these two techniques together could exlain all the charge transfer changes on an electrode. Ferricyanide also could act as a mediator for some electrochemical rections and thereby enhancing the signal since these reaction has a good electron transfer kinetics on almost all the electrodes.

Thanks to all for the detailed answers. Really appreciate it. It helps.