Phase separation in lipid bilayer membranes induced by intermixing at a boundary of two phases with different components

• Coalescence of two self-spreading supported-lipid-bilayers were observed.
• Raft-like domain is formed by coalescence between DOPC/SM membrane and DOPC/Chol one.
• When Chol is incorporated into a gel phase, micrometer-scaled Lo domains form.
• The Lo domain size made from DPPC is smaller than that from SM.

We have demonstrated that dynamic phase separation is induced by coalescence of two self-spreading supported lipid bilayers (SLBs) with different components. Coalescence between a phosphocholine/sphingolipid SLB and a phosphocholine/cholesterol one forms raft-like liquid ordered (Lo) domains, which can be observed by fluorescence microscopy at the boundary of two phases. This phase separation process indicates that lipid molecules, such as sphingolipid and cholesterol, are intermixed. When saturated phospholipid is used instead of sphingolipid, small Lo domains are formed. Cholesterol is harder to incorporate with domains of saturated phospholipid than that of sphingolipid. This technique is very useful for observation of lipid–lipid interactions.

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