Monitoring of membrane collapse and enzymatic reaction with single giant liposomes embedded in agarose gel

Giant liposomes are often used as models for studies on cell membranes. We embedded giant liposomes in agarose gel to fix them for assays. Giant liposomes of dioleoylphosphatidylcholine were embedded in 1% (w/v) agarose gel with a low melting temperature: While only 20–25% of giant liposomes survived embedment, their size distribution was unaffected. Using a confocal laser scanning microscope, we monitored dynamic changes in individual agarose gel-embedded giant liposomes induced by the addition of a surfactant (Triton X-100). The permeation and collapse could be clearly discriminated from each other. Invaginated buds on liposome membranes could also be captured as intermediate structures. Additionally, an enzymatic (β-glucosidase) reaction encapsulated within the target liposome was triggered by the external addition of a non-fluorescent substrate and successfully monitored. These results suggest that embedment in agarose gel is useful for the simple fixation of giant liposomes for biochemical and biophysical assays.