Electrodiffusion through Pores in Supported Lipid Bilayers on PEDOT:PSS Electrodes: Bridging Equivalent Circuits and FEM Simulations

Supported lipid bilayers (SLBs) serve as essential model systems in studies of membrane biophysics, biosensing, and bioelectronic interfaces. In particular, SLBs formed on conductive polymer (CP) electrodes constitute a new platform to study ion transport across ion channels or the activity of pore-forming toxins through the use of electrochemical impedance spectroscopy (EIS). However, unavoidable pores in the SLB limit detection sensitivity in, e.g., biosensing applications. In this work, we rigorously assess the impact of such ion-conducting pathways on EIS measurements by combining an analytically derived equivalent circuit model (a-ECM) with finite-element-method (FEM) simulations. We start by considering simple, idealized conditions to build intuition regarding the pore-related resistance and capacitance contributions, directly comparing a-ECM predictions with full Poisson-Nernst-Planck (PNP)-based FEM simulations. Subsequently, we introduce additional complexities, including a thin water layer at the SLB/CP interface, SLB surface charge effects, and nonaxisymmetric pore locations, to progressively refine our model. Finally, by extending our analysis to a distribution of pores, we demonstrate how our insights can be used to estimate the pore size and density from experimental EIS data of SLBs formed on PEDOT:PSS electrodes. By bridging intuitive circuit models with accurate FEM simulations, our work provides practical guidelines for interpreting EIS spectra and extracting meaningful physical parameters associated with membrane pores.