Assembling polyelectrolytes and porphyrins into hollow capsules with laser-responsive oxidative properties

Photoactive microcapsules consisting of the polyelectrolytes poly(allylamine hydrochloride) and poly(styrene sulfonate) and the tetrapyrrolic dye meso-tetrakis(4-sulfonatophenyl) porphine (TPPS) are fabricated using the technique of layer-by-layer self-assembly. Microscopy images and spectroscopy measurements showed the formation of stable capsules with the porphyrin embedded mainly in the shell wall. Interaction of TPPS with polyelectrolytes in solution and on a quartz slide revealed that in the multilayer system TPPS exists as tetranion along with the formation of some H aggregates. Irradiating the fluorescent capsules using a standard xenon lamp with high ultraviolet emission had no effect on the morphology of the capsules. However, illumination with laser light in the presence of an oxidizing agent led to disruption of the capsule wall. The ability of the porphyrin to induce the formation of active oxygen species on irradiation with suitable light leads to the disruption of the capsules. Such porphyrin-incorporated capsules could have the potential to be developed into a remote releasing system, which can be opened with lower laser intensity than existing systems.