In this work, the characterization of release events from liposomes has been addressed quantitatively by an electrochemiluminescence (ECL) imaging strategy. First, ECL reagents ([Ru(bpy)3] 2+ and tripropylamine) have been encapsulated in sealed giant asymmetrical liposomes (100 µm in diameter) made of DOPG/DOPC phospholipids. After sedimentation on an ITO (Indium Tin Oxide) electrode material, the opening of liposomes was then triggered by polarization of the surface. Under these conditions, amperometry, epifluorescence and ECL were combined and synchronized to monitor and image the rupture of giant liposomes through the release and subsequent ECL emission of their redox content. Amperometry allowed the quantification of the content released from single liposomes. The location and status of liposomes (closed or opened) was assessed by epifluorescence. ECL provided imaging the efflux of matter after liposome opening. This original ECL imaging approach favorably compares to strictly photoluminescent or electrochemical techniques and appears adapted to the investigation of membrane rupture / permeation events.

The permeabilization of liposomes by melittin, an antimicrobial peptide (AMP), has been studied by an electrochemiluminescence (ECL) imaging strategy. The methodology consisted first of encapsulating ECL reagents in sealed giant asymmetrical liposomes (100 μm in diameter) made of DOPG/DOPC phospholipids (i.e., 1,2-dioleoyl-sn-glycerol-3-phospho-(1′-rac-glycerol) sodium salt/1,2-dioleolyl-sn-glycero-3-phosphocholine). Then liposomes were placed on an indium tin oxide electrode coated with poly-l-lysine to avoid any membrane poration/permeabilization through polarization of the electrode surface. Finally, the addition of melittin (from 10 μM to 100 nM in concentration) enabled the permeabilization of the lipid membrane followed by the liposome content release and subsequent light generation through the ECL reagents oxidation processes. Interestingly, at a melittin concentration of 10 μM, two successive leakages occurring on the same liposome could be imaged. Combination of ECL and photoluminescence imaging allowed comprehensive monitoring of the permeabilization and content release of a single liposome. This ECL imaging approach opens interesting perspectives to characterize the instant release of vesicle content upon permeabilization by AMPs or other membrane-active species.