Two-Photon Induced Fluorescence Energy Transfer in Polymeric Nanocapsules Containing CdSexS1-x/ZnS Core/Shell Quantum Dots and Zinc(II) Phthalocyanine

We report activation of a photodynamic therapy photosensitizer, zinc phthalocyanine, by Forster resonant energy transfer (FRET) from two-photon absorption excited CdSexS1-x/ZnS quantum dots coencapsulated in multifunctional biocompatible polymer nanocapsules. Polymer nanocapsules (100 nm size) were prepared via solvent/evaporation method using Poloxamer 403 as the polymer component, Cremophor EL as the surfactant and mixture of silicone oil with hydrogenated caprylyl olive oil esters as the oil phase. UV-vis NIR absorption and multiphoton fluorescence studies confirmed successful coencapsulation of both components of the FRET system. The energy transfer between the quantum dots as donors and Zn phthalocyanine molecules as acceptors was studied using steady-state photoluminescence and time-correlated single photon counting techniques. The changes in the lifetime of the QDs emission indicate that the excitation of ZnPc occurs not only through reabsorption but also through FRET. The generation of the reactive oxygen species was confirmed by formation of the nonfluorescent endoperoxide derivative of fluorescent 9,10-anthracenediylbis(methylene)dimalonic acid sodium salt under irradiation of the nanocapsules co-loaded with both QDs and ZnPc.