Two-Dimensional Continuous Extraction in Multiphase Lipid Bilayers To Separate, Enrich, and Sort Membrane-Bound Species

A new method is presented to separate, enrich, and sort membrane-bound biomolecules based on their affinity for different coexisting lipid phases in a supported lipid bilayer using a two-dimensional, continuous extraction procedure. Analogous to classic liquid–liquid phase extraction, we created two distinct lipid phases in our planar membrane system: a liquid-ordered (<i>l</i><sub>o</sub>) phase and a liquid-disordered (<i>l</i><sub>d</sub>) phase arranged in parallel stripes inside a microfluidic device. Membrane-bound biomolecules in an adjacent supported lipid bilayer are convected in plane along the microfluidic channel and brought into contact with a different lipid phase using hydrodynamic force. A mixture of two lipid species, a glycolipid and a phospholipid, with known affinities for the two lipid phases employed here are used to demonstrate continuous extraction of the lipid-microdomain preferring glycolipid to the <i>l</i><sub>o</sub> phase, while the phospholipid remains primarily in the <i>l</i><sub>d</sub> phase. In this demonstration, we characterize the performance of this affinity-based separation device by building models to describe the velocity profile and transport in the two-phase coexistent membrane. We then characterize the impact of residence time on the extraction yield of each species. This new procedure sorts membrane species on the basis of chemical properties and affinities for specific lipid phases within a membrane environment near physiological conditions, critical for extending this method to the separation of lipid-linked proteins and transmembrane proteins while minimizing denaturation. This platform could facilitate the separation and identification of lipid membrane domain residents, or the characterization of changes in membrane affinity due to post-translational modifications or environmental conditions.