The optimal accessibility of functional groups on polymeric nanosized vesicles was investigated with copper-free clickable probes as a model system. Cu-free clickable polymersomes were developed either through co-assembly of end group modified amphiphilic block copolymers or by introduction of the reactive moieties on preformed vesicles. For the co-assembly approach, the highest degree of availability was obtained for the most hydrophilic functional group, whereas hydrophobic species were unable to react as efficiently since they were seemingly buried in the membrane. Post-self-assembly introduction led to good results for all three examined moieties whereby surface saturation was reached above a certain percentage of immobilised probes. Finally, we demonstrated that protrusion of functional entities from the membrane corona via a longer hydrophilic segment of the block-copolymer significantly enhances the accessibility.