Confocal-Raman Microscopy Characterization of Supported Phospholipid Bilayers Deposited on the Interior Surfaces of Chromatographic Silica

A common approach to exploring the structure and dynamics of biological membranes is through the deposition of model lipid bilayers on planar supports by Langmuir-trough or vesicle-fusion methods. Planar-supported lipid bilayers have been shown to exhibit structure and properties similar to those of lipid-vesicle membranes and are suitable for biosensing applications. Investigations using these planar-membrane models are limited to high-sensitivity methods capable of detecting a small population of molecules at the interface between a planar support and aqueous solution. In this work, we present evidence that supported-lipid bilayers can be deposited by vesicle fusion onto the interior surfaces throughout the wide-pore network of chromatographic silica particles. The thickness of a 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) film and headgroup spacing are consistent with a single bilayer of DMPC deposited onto the pore surfaces. The high specific surface area of these materials generates phospholipid concentrations easily detected by confocal-Raman microscopy within an individual particle, which allows the structure of these supported bilayers to be investigated. Raman spectra of porous-silica-supported DMPC bilayers are equivalent to spectra of DMPC vesicle membranes, both above and below their melting phase transitions, suggesting comparable phospholipid organization and bilayer structure. These porous-silica-supported model membranes could share benefits that planar-supported lipid bilayers bring to biosensing applications, but in a material that overcomes the limited surface area of a planar support. To test this concept, the potential of these porous-silica-supported lipid bilayers as high-surface-area platforms for label-free Raman-scattering-based protein biosensing is demonstrated with detection of concanavalin A selectively binding to a lipid-immobilized mannose target.