Solvent-Assisted Lipid Bilayer Formation on Silicon Dioxide and Gold

Abstract

Planar lipid bilayers on solid supports mimic the fundamental structure of biological membranes and can be investigated using a wide range of surface-sensitive techniques. Despite these advantages, planar bilayer fabrication is challenging, and there are no simple universal methods to form such bilayers on diverse material substrates. One of the novel methods recently proposed and proven to form a planar bilayer on silicon dioxide involves lipid deposition in organic solvent and solvent exchange to influence the phase of adsorbed lipids. To scrutinize the specifics of this solvent-assisted lipid bilayer (SALB) formation method and clarify the limits of its applicability, we have developed a simplified, continuous solvent-exchange version to form planar bilayers on silicon dioxide, gold, and alkanethiol-coated gold (in the latter case, a lipid monolayer is formed to yield a hybrid bilayer) and varied the type of organic solvent and rate of solvent exchange. By tracking the SALB formation process with simultaneous quartz crystal microbalance-dissipation (QCM-D) and ellipsometry, it was determined that the acoustic, optical, and hydration masses along with the acoustic and optical thicknesses, measured at the end of the process, are comparable to those observed by employing conventional fabrication methods (e.g., vesicle fusion). As shown by QCM-D measurements, the obtained planar bilayers are highly resistant to protein adsorption, and several, but not all, water-miscible organic solvents could be successfully used in the SALB procedure, with isopropanol yielding particularly high-quality bilayers. In addition, fluorescence recovery after photobleaching (FRAP) measurements demonstrated that the coefficient of lateral lipid diffusion in the fabricated bilayers corresponds to that measured earlier in the planar bilayers formed by vesicle fusion. With increasing rate of solvent exchange, it was also observed that the bilayer became incomplete and a phenomenological model was developed in order to explain this feature. The results obtained allowed us to clarify and discriminate likely steps of the SALB formation process as well as determine the corresponding influence of organic solvent type and flow conditions on these steps. Taken together, the findings demonstrate that the SALB formation method can be adapted to a continuous solvent-exchange procedure that is technically minimal, quick, and efficient to form planar bilayers on solid supports.

Self-Assembly Formation of Lipid Bilayer Coatings on Bare Aluminum Oxide: Overcoming the Force of Interfacial Water

“…By contrast, on silicon oxide, the final frequency and energy dissipation shifts were −26.2 ± 0.6 Hz and 0.3 ± 0.1 × 10 −6 , respectively, which are in agreement with past measurements. 48 To determine if the lipid layer on aluminum oxide was globally homogeneous, we measured the nonspecific adsorption of bovine serum albumin, which was nearly negligible (∼1 Hz). By contrast, BSA adsorption onto a bare aluminum oxide surface yielded a frequency shift of approximately −28 Hz, and we conclude that the attached lipid layer covers more than 96% of the aluminum oxide substrate ( Figure S5, Supporting Information).…”

Total internal reflection fluorescence microscopy for determination of size of individual immobilized vesicles: Theory and experiment

“…8 Such systems can be fabricated via adsorption of vesicles without or with subsequent spontaneous or peptide-induced rupture 8,9 or via the "solventassisted" procedure. 10 The corresponding mass uptake can be determined optically by ellipsometry, waveguide lightmode spectroscopy and surface plasmon resonance, [11][12][13] or by quartz crystal microbalance. 12 Vesicles directly attached to a support are however deformed.…”

Kinetics of Single-Enzyme Reactions on Vesicles: Role of Substrate Aggregation

“…to be of the order of 2 µm 2 /c. [38][39][40] If e.g. the vesicle radius is 50 nm, its area is s 3 × 10 4 nm 2 .…”