Formation of Tethered Bilayer Lipid Membranes on Gold Surfaces: QCM-Z and AFM Study

Recently, tethered bilayer lipid membranes (tBLMs) have shown high potential as biomimetic systems due to their high stability and electrical properties, and have been used in applications ranging from membrane protein incorporation to biosensors. However, the kinetics of their formation remains largely uninvestigated. By using quartz crystal microbalance with impedance analysis (QCM-Z), we were able to monitor both the kinetics and viscoelastic properties of tether adsorption and vesicle fusion. Formation of the tether monolayer was shown to follow pseudo-first-order Langmuir kinetics with association and dissociation rate constants of 21.7 M^-1 s^-1 and 7.43 x 10^-6 s^-1, respectively. Moreover, the QCM-Z results indicate a rigid layer at the height of deposition, which then undergoes swelling as indicated by AFM. The deposition of vesicles to the tether layer also followed pseudo-first-order Langmuir kinetics with observed rate constants of 5.58 x 10^-2 and 2.41 x 10^-2 s^-1 in water and buffer, respectively. Differential analysis of the QCM-Z data indicated deposition to be the fast kinetic step, with the rate-limiting steps being water release and fusion. Atomic force microscopy pictures taken complement the QCM-Z data, showing the major stages of tether adsorption and vesicle fusion, while providing a road map to successful tBLM formation.