Competing Interactions of Fatty Acids and Monoglycerides Trigger Synergistic Phospholipid Membrane Remodeling.

Using quartz crystal microbalance-dissipation and time-lapse fluorescence microscopy, we demonstrate that adding mixtures of lauric acid (LA) and glycerol monolaurate (GML), two of the most biologically active antimicrobial fatty acids and monoglycerides, to a supported lipid bilayer triggers concurrent tubule and bud formation, which unexpectedly results in synergistic phospholipid membrane remodeling that far exceeds the effects of GML or LA alone. Together, GML and LA drive pearling instability, dynamic transformation of buds into tubules and vice versa, and extensive membrane lysis. The most pronounced effects occurred with equimolar concentrations of GML and LA, highlighting that synergistic membrane disruption arises from competition for the lipid supply to buds and tubules and an inability to relieve membrane strains. These findings offer a conceptually new model to explain how fatty acid and monoglyceride interactions can trigger phospholipid membrane remodeling events relevant to various biophysical and biological systems.

Nanoplasmonic Ruler for Measuring Separation Distance between Supported Lipid Bilayers and Oxide Surfaces.

Unraveling the details of how supported lipid bilayers (SLBs) are coupled to oxide surfaces is experimentally challenging, and there is an outstanding need to develop highly surface-sensitive measurement strategies to determine SLB separation distances. Indeed, subtle variations in separation distance can be associated with significant differences in bilayer-substrate interaction energy. Herein, we report a nanoplasmonic ruler strategy to measure the absolute separation distance between SLBs and oxide surfaces. A localized surface plasmon resonance (LSPR) sensor was employed to track SLB formation onto titania- and silica-coated gold nanodisk arrays. To interpret measurement data, an analytical model relating the LSPR measurement response to bilayer-substrate separation distance was developed based on finite-difference time-domain (FDTD) simulations and theoretical calculations. The results indicate that there is a larger separation distance between SLBs and titania surfaces than silica surfaces, and the trend was consistent across three tested lipid compositions. We discuss these findings within the context of the interfacial forces underpinning bilayer-substrate interactions, and the nanoplasmonic ruler strategy provides the first direct experimental evidence comparing SLB separation distances on titania and silica surfaces.