After incubation of APCN microcapsules in a solution of CyPC and subsequent purification of the capsules, the microcapsules remained fluorescent. This indicates that CyPC was retained after centrifugation, washing in water, and resuspension of the capsules in water (Figure ). CLSM micrographs show that the fluorescence was localized on the outside of the APCN shell (Figure ). Thus, CyPC did not diffuse through the whole membrane but selectively stained a thin outer layer of the capsule wall. The selective modification of the capsule surface with PEG-cholesterol should also allow the outer surface of the capsules to be decorated with other useful moieties, for example, functional groups for click chemistry to attach biomolecules.