The GUVs maintain their integrity and neither membrane perturbations nor fusion events are observed. To investigate whether fusion or hemifusion can occur between GUVs, we mixed two GUV populations labelled with Rh-DOPE or DiO respectively. These GUVs were incubated with 25 µg/ml SNPs-30@BSA for 30 min. After this time, vesicles were observed to adhere but we could not detect any transfer of fluorescent lipids between the oppositely labelled GUVs (Fig. ). These observations indicate GUV adhesion where the membrane rearrangements required for hemifusion or full fusion are suppressed. In this case, the increase in particle size due to the BSA corona likely holds the membranes apart at too great a distance for the membranes to directly interact, where sufficient membrane bending is not permitted to drive the formation of a fusion stalk with an estimated energy barrier of 20-35 kBT .