Employing Two Different Quartz Crystal Microbalance Models To Study Changes in Viscoelastic Behavior upon Transformation of Lipid Vesicles to a Bilayer on a Gold Surface

Abstract

By analyzing the viscoelastic properties of two distinct layers, a layer of "soft" vesicles and a "rigid" bilayer, we have created a model system to permit the study of film behavior in the region of nonlinear mass and frequency change (non-Sauerbrey). The structural transformation of lipid vesicles to a bilayer is shown to be accompanied by significant changes in their physical properties. After the adsorption and saturation of intact vesicles on gold surfaces, the adsorbed vesicle layer exhibits a soft, water-rich, viscoelastic state. The AH peptide, a vesicle-destabilizing agent, is then added to trigger the formation of a much thinner (approximately 5 nm), compact, and rigid bilayer. In this study, we used the quartz crystal microbalance with dissipation technique. Large non-Sauerbrey frequency and energy dissipation changes characterize the viscoelastic nature of adsorbed intact vesicle films thicker than approximately 10 nm. Once the transformation is complete, the frequency changes along with zero energy dissipation for sufficiently thin films (t approximately 5 nm) were effectively modeled with the Sauerbrey equation. Furthermore, we checked the validity of the Voigt-Voinova model in which the quartz substrate is treated as a Voigt element, which is beyond the Sauerbrey description. The calculations treating the film as having a constant viscosity agreed well with the Voigt-Voinova model. These results were compared to calculations done using the electromechanical (EM) model, which does not require a series expansion. The Voigt-Voinova results were in excellent agreement with the EM model, providing evidence that the expansion used in their study is quite accurate.

Role of Caustic Addition in Bitumen–Clay Interactions

“…3, 4 and 5), 40,42 by considering the shift in both the sensor (5) where h is the thickness, is the density, is the viscosity, is the shear modulus and is the angular frequency.…”

Model Membrane Platforms for Biomedicine: Case Study on Antiviral Drug Development

“…Second, proteinaceous components may modulate the properties of the lipid membrane itself, thus affecting the binding interaction of the AH peptide to lipid and/or other protein biologically relevant for studying macromolecular interaction kinetics. Recent studies have investigated how AH peptide affects the film properties of the intact vesicle platform [40,42]. With the collection of characterization data, there is an increasing amount of information about the molecular determinants of the target interaction.…”

“…In this outlook, we introduce areas where we envision engineering strategies may further aid antiviral drug development. By assembling an in situ assay to predict virus particle rupture [40][41][42][43], the work reviewed here has established a cost-effective tool to rapidly screen and functionally characterize antiviral drug candidates in minutes rather than days. Based on this preliminary format, the system can be improved by increasing sensitivity to reduce the amount of peptide material required and/or adapting the signal response to a more readily high-throughput measurement technique.…”

“…As a case study example of a viral pathogen target, we have selected the hepatitis C virus (HCV) and discuss how engineering strategies identified a previously unknown functional activity encoded within the HCV nonstructural 5A (NS5A) protein. By employing a model membrane platform to mimic the host cell membrane interface upon which viral genome replication occurs, a striking ability to lyse lipid vesicles was discovered within the NS5A N-terminal amphipathic, a-helix (AH) [40][41][42][43].…”

Real-time examination of aminoglycoside activity towards bacterial mimetic membranes using Quartz Crystal Microbalance with Dissipation monitoring (QCM-D)

“…The frequency change (Δf) from the QCM-D is related to the change in mass [60], while the dissipation output (ΔD) can be used for the qualitative profiling of structural changes in the bilayer. A decrease in Δf value implies the addition of mass onto the sensor, whereas an increase in ΔD indicates that the lipid bilayer is becoming less rigid, loosening or thickening [60][61][62][63].…”