Scanning electrochemical microscopy. 56. Probing outside and inside single giant liposomes containing Ru(bpy)32+

Giant liposomes containing Ru(bpy)(3)(2+) (bpy = 2,2'-bipyridine) were prepared as model systems for biomembranes and cells and studied by scanning electrochemical microscopy (SECM). Conical carbon fiber tips of submicrometer size were used to approach, image, and puncture individual liposomes immobilized on glass substrates. SECM images of the liposomes were obtained, and the leakage of Ru(bpy)(3)(2+) through the lipid membrane was probed. The tip was also pushed into liposomes and characteristic breakthrough transients, corresponding to liposomes with different compartmental configurations, were obtained. Voltammograms were obtained with the tip inside a single liposome after breaking through the membrane, and the influx of mediator and efflux of encapsulant after puncture could be observed.