Electrochemical impedance spectroscopy of tethered-bilayers

Gintaras Valincius (Institut of Biochemistry, Vilnius, Lituania)

Electrochemical impedance (EI) spectroscopy is one of the most advanced techniques to study the electrical properties of bilayer lipid membrane systems. The applicability of this method, however, is heavily dependent on modelling. Even for structurally simple biomimetic systems such as black lipid membranes, the EI spectral features may exhibit quite sophisticated properties that require adequate mathematical treatment to retrieve physically relevant information about the system. The situation is even more complicated for the tethered to the surface bilayers because of the structural complexity of such systems. In this work, we analyze the frequency spectra of tethered bilayers using a concept of distributed-parameter networks. We demonstrate that the presence of defects in tethered bilayer systems result in specific low frequency features in the EI spectra. The analysis of these features allows assessing the physical parameters of the tethered bilayer system such as the specific resistance and thickness of the electrolyte reservoir separating the bilayer and metal surface, as well as the capacitance of the metal/reservoir interface. In addition, we demonstrate that, in certain cases, the presence of these defects leads to the constant-phase element (CPE) type of impedance. The values of the exponent of CPE may be used to estimate the defect density as well as to asses the electrical heterogeneity of the submembrane reservoir located between the electrode and the bilayer. We analyze EI spectral data in the context of the Alzheimer's disease-related water-soluble prefibrillar amyloid â (Aâ) peptide and pore-forming á-hemolysin ( á-HL) protein interactions with tethered bilayers. Although the literature suggests that the membrane damage triggered by Aâ and á-HL occurs by qualitatively distinct mechanisms, both proteins trigger similar EI spectral changes and dramatically increase membrane conductance. We now demonstrate how EI spectral analysis allows one to distinguish between these two different mechanisms.

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