Real-time nanoplasmonic sensing of three-dimensional morphological changes in a supported lipid bilayer and antimicrobial testing applications

We report the development of a real-time localized surface plasmon resonance (LSPR) biosensing strategy to detect three-dimensional morphological changes in a supported lipid bilayer (SLB) on a plasmonic substrate. The sensing concept advances on past efforts to detect subtle conformational changes in adsorbed biomacromolecules by demonstrating the capability to track large-scale, complex adsorbate shape changes and to classify different types of shape changes based on specific, multi-step measurement signatures. To validate this concept, we tested the addition of antimicrobial fatty acids, monoglycerides, and surfactants in micellar form to the SLB platform, which triggered specific three-dimensional membrane morphological changes such as tubule or bud formation along with solubilization. Experimentally, the different remodeling events were detected by distinct measurement signatures related to the shape and size of lipid protrusions that formed and evolved over time, which agreed well with a newly developed theoretical model. Our conceptual approach and formalism can be used in a wide range of biosensing techniques, including not only LSPR but also surface plasmon resonance (SPR) and total internal reflection fluorescence (TIRF) microscopy. These sensing capabilities are advantageous for evaluating the mechanisms of antimicrobial drug candidates and other membrane-active compounds, and the measurement strategy can be applied to a wide range of biomimetic lipid compositions.