Local and transient permeation events are associated with local melting of giant liposomes.

We reveal that the gel to fluid phase transition causes spherical membrane vesicles to release a finite number of molecules in several consecutive and localized events. By locally melting Giant Unilamellar lipid Vesicles (GUVs), using an optically trapped gold nanoparticle (AuNP) as a local heat source, we establish a local phase transition on the spherical GUV membrane clearly visualized using a phase sensitive fluorescent marker. We measure transient permeation events through this transition zone visualized as de-quenching of calcein as it escapes the interior of the GUV. Since biological membranes share several features with melting membranes, like nanoscale domain formation and critical density fluctuations, similar passive membrane transport could potentially be abundant in living cells.