Development of Novel Separation and Sensor Platforms Based on Polymerized Phospholipid Vesicles

Abstract

Analyte-membrane and analyte-membrane receptor interactions are related to drug absorption through transmembrane diffusion and cellular signal transduction, respectively. Therefore, the study of these interactions plays key roles in new drug development. Membrane-based chromatography using artificial phospholipid vesicles as stationary phases provides a high-throughput approach to screen analyte-membrane interactions. Additionally, by incorporating membrane receptors into the vesicle stationary phases, analyte-membrane receptor interactions can be studied. However, the inherent instability of artificial phospholipid vesicles limits their application. This work has explored the utilization of polymerized phospholipid vesicles in developing highly stable separation and sensing platforms based on analyte-membrane or analyte-membrane receptor interactions. The processes of vesicle polymerization using polymerizable lipids and polymer scaffolding are also characterized and optimized.In order to improve the stability of stationary phases in membrane-based chromatography, polymerized phospholipid vesicles made of polymerizable bis-SorbPC lipids were covalently immobilized on the inner wall of silica capillaries to serve as stationary phases. The polymerized vesicle stationary phases showed enhanced stability against drying/rehydration and shear forces compared to non-polymerizable counterparts. Aliphatic amines were separated using the polymerized vesicle stationary phases based on their different interactions with the vesicle membranes in both open-tubular capillary liquid chromatography (CLC) and capillary electrochromatography (CEC) formats. This application broadens the range of membrane-based stationary phases to include polymerized phospholipid vesicles, which provide enhanced stability. Biosensors that detect ligands based on ligand-receptor interactions using artificial phospholipid vesicles generally do not allow ligand identification. A pull-down assay was developed using novel silica core-polymerized vesicle shell particles combined with MALDI-MS for the simultaneous detection and identification of peptide/protein ligands that bind to membrane receptors. The polymerized vesicle shell survived MS vacuum conditions and showed higher stability against organic solvent treatment compared to non-polymerizable counterparts. As a proof of concept, cholera toxin binding subunit (CTB) was successfully detected using ganglioside GM1-functionalized core-shell particles. The assay has the potential to differentiate among multiple ligands that bind to the same receptor and identify unknown ligands in a complex ligand mixture.In addition to using polymerizable lipids, polymer scaffolding is also used to stabilize phospholipid vesicles, although the formation of polymer scaffolds in nanometer-sized vesicles is difficult to characterize. Polymer scaffolds were successfully synthesized inside vesicles composed of non-polymerizable DOPC lipids (100-200 nm in diameter), by doping small molecule linear monomers and cross-linkers into the vesicle lamellar region followed by photochemical initiation. It was found that DOPC vesicles containing polymer scaffolds formed by different linear monomers showed similar stability against surfactant treatment. This study adds new insights to the current understanding and characterization of the polymer scaffolding process.