Electrochemical impedance of randomly distributed defects in tethered phospholipid bilayers: Finite element analysis

Finite element analysis (FEA) reveals that random distribution of defects in tethered bilayers results in qualitatively similar electrochemical impedance spectroscopy (EIS) response as bilayers with regularly arrayed defects. Such similarity leads to a broader conclusion that the microheterogeneity of tBLMs, which is possibly always the case in real systems may be of lesser importance as far as qualitative aspects of the system are interrogated by the EIS. This means that the analytical solutions of the EIS response may be used to tentatively assess physical parameters and predict variations of EIS curves in the course of interaction between the phospholipid membranes and proteins as well as other membrane damaging agents. While qualitatively similar EIS spectra exhibit a number of quantitative differences. We found that random distribution of defects results in a decrease of the measured conductivity of tBLMs, and the upward shift of the admittance phase minimum which is always present in tBLMs containing defects, and the downshift of the position of that minimum on the frequency scale. Taking into account these features we proposed a simple algorithm that allows calculation of defect density as well as evaluation of the physical size of defects in membrane.