Characterization of Double Layer Alterations Induced by Charged Particles and Protein–Membrane Interactions Using Contactless Impedance Spectroscopy

Abstract

Double layer interactions between charged particles and surfaces play a vital role in a variety of technical and biological systems because they determine the stability of, e.g., protein-membrane biointerfaces. The underlying theoretical principle is based on the overlap of two different double layers that induce surface charges to be shifted to a new equilibrium distribution, which can be approximated by the Poisson-Boltzmann equation. In the present work we show theoretical and experimental results involving double layer capacitance of surfaces that exhibit charge regulation behavior. Charge regulation is an important parameter to consider when investigating protein-membrane interactions because it defines surface properties between ideal constant charge and constant potential behavior. In this work we introduce a novel theoretical model that also includes charge regulation behavior and can assess changes of double layer disruptions at TiO(2) and supported lipid-bilayers (SLB). The selected surfaces represent important biointerfaces that can be found on implants or cell membranes. We also demonstrate that contactless impedance spectroscopy is well suited to measure double layer capacitance interactions using differently charged silica beads. The combination of a theoretical model with experimental data allowed us further to identify charge regulation effects during protein adsorption (BSA and Annexin V) events at supported lipid-bilayers (SLB) used as a simple cell membrane model. Finally, the first indications of changed charge regulation behavior during protein surface crystallization events were also documented.