Solvent‐Assisted Lipid Bilayer Formation on Au Surfaces: Effect of Lipid Concentration on Solid‐Supported Membrane Formation

Abstract

Solvent-assisted lipid bilayer (SALB) formation has emerged as a versatile approach in forming supported lipid membranes (SLBs) on metal surfaces, interesting platforms for transducing a biological signal to an electrical readout where vesicle rupture is not straightforward. In this work, the effect of the lipid concentration in the organic solvent, a key parameter controlling SALB, is addressed in the low and high concentration limits of DPPC lipid on a Au surface.Quartz crystal microbalance with dissipation (QCM-D) responses are correlated with atomic force microscopy (AFM) topographic and nanomechanical measurements. Upon SALB completion at both concentrations, QCM-D and AFM topographical characterization suggest the formation of thin, although incomplete, lipid layers at the Au-liquid interface, with frequency and dissipation plateau values departing from well-established homogeneous SLB responses. Nanomechanical analysis reveals the presence of mostly monolayers at low concentration due to lack of lipid material, while at high concentration, excess of lipid material leads to coexistence of diverse structures. Their formation stems from the SALB formation mechanism, based on lyotropic transformations upon solvent exchange, which differs from customarily vesicle rupture. Such mechanism leads to peculiar two-step features in approach force curves on SLBs pointing towards a decoupling in bilayer leaflets when supported.

Artificial Cell Membrane Platforms by Solvent-Assisted Lipid Bilayer (SALB) Formation

“…18 The surfaces with similar roughnesses (silicon dioxide, 1.2 ± 0.1 nm; gold, 0.9 ± 0.2 nm) were used in this study as the surface roughness can affect the conformation of the lipid layer formed by the SALB method. 35 However, by vesicle fusion, absorbed zwitterionic lipid vesicles only ruptured on silicon dioxide (Figure 2B), not gold (Figure 2D), as denoted by frequency (Δf) and energy dissipation (ΔD) shifts consistent with lipid bilayer formation (−26 ± 1 Hz and (0.3 ± 0.2) × 10 −6 , respectively) in the QCM-D measurement. The hydration mass of SALB-formed lipid bilayers on gold was larger than those on silicon dioxide, indicating the unruptured vesicles on gold might be caused by a strong hydration force based on the Hamaker constants greater than silicon dioxide.…”

“…Through quartz crystal microbalance with dissipation (QCM-D) monitoring, it was demonstrated that complete SLBs were fabricated onto both silicon dioxide (Figure A) and the gold surface (Figure C) by the SALB approach . The surfaces with similar roughnesses (silicon dioxide, 1.2 ± 0.1 nm; gold, 0.9 ± 0.2 nm) were used in this study as the surface roughness can affect the conformation of the lipid layer formed by the SALB method . However, by vesicle fusion, absorbed zwitterionic lipid vesicles only ruptured on silicon dioxide (Figure B), not gold (Figure D), as denoted by frequency ( Δf ) and energy dissipation ( ΔD ) shifts consistent with lipid bilayer formation (−26 ± 1 Hz and (0.3 ± 0.2) × 10 –6 , respectively) in the QCM-D measurement.…”

QCM‐D Study of the Formation of Solid‐Supported Artificial Lipid Membranes: State‐of‐the‐Art, Recent Advances, and Perspectives

“…[56,57] Typical QCM-D sensors coated with SiO 2 , Au, and Al 2 O 3 are polycrystalline surfaces with nanoscale roughness. [38,58] As a matter of fact, surface roughness and topography are important parameters in many biotechnological applications that require rather rough and topographically complex surfaces. SLBs supported onto corrugated surfaces are relevant platforms where membrane curvature can be directly addressed.…”

Advances in Cell-Conductive Polymer Biointerfaces and Role of the Plasma Membrane

“…Recently, a new strategy, namely, solvent-assisted lipid bilayer (SALB) method, has been proposed to support the formation of bilayers on diverse materials (i.e., gold, aluminum, oxide, silicon dioxide, graphene, and CPs), being not strictly limited by the material surface and lipids composition. − In the SALB approach, the lipid vesicles adsorption and planar assembling on the substrate occurs inside a microfluidic channel, as shown in Figure B. Here, the solvent mixture of isopropanol and water, in which the lipids are suspended, is slowly replaced with an aqueous buffer, minimizing the effect of the surface tension at the lipid–substrate interface .…”