(221e) Modeling Protein Adsorption with Electrochemical Impedance Spectroscopy

Electrochemical impedance spectroscopy (EIS) tracks electrical signals at electrode/electrolytic solution interfaces, allowing one to monitor interactions occurring at the electrode surface by tracking impedance. Impedance is the opposition to the flow of electrons or current in alternating current (AC) signals. EIS can be used to record electrode capacitance and charge transfer kinetics, providing valuable mechanistic information for a desired system. It is used to describe a system's response to an AC signal or voltage for a range of frequencies at a steady state. Impedance is a complex number combination of resistance, capacitance, and inductance in the system of interest, and each activity (including binding, film growth or reactions) can be characterized as a component of impedance. EIS has become a powerful technique in the study of corrosion, semiconductors, and electro-organic synthesis. This type of spectroscopy can also be applied to the study of biological systems. EIS can be used to monitor biological activities such as antibody-antigen interactions and non-specific protein adsorption. In this study, we validate the application of EIS in the understanding of nonspecific protein adsorption on gold. First, EIS was used to record the impedance resulting from the application of a sinusoidal AC current applied to a gold electrode in an aqueous electrolyte at a specific frequency as a function of time. The adsorption of bovine serum albumin (BSA) from phosphate buffer saline (PBS) onto the gold surface was then tracked at similar conditions. From these studies, the binding kinetics of the BSA to the gold were extracted. During EIS studies, the AC current is applied at a given DC bias on the gold. By varying the bias on the gold, the effects of electrostatics and mass transfer were considered. Here, small voltages were applied to the gold wire for short amounts of time (>1 minute) following electrode exposure to BSA in PBS, and the response of the system was recorded. The resulting BSA binding to the gold surface was characterized as a function of the sign and magnitude of the applied DC potential, the time over which the potential was applied, and the applied potential prior to the application of the potential of interest.