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Polystyrene and Poly(ethylene glycol)-b-Poly(ε-caprolactone) Nanoparticles with Porphyrins: Structure, Size, and Photooxidation Properties.

The transport of a photosensitizer to target biological structures followed by the release of singlet oxygen is a critical step in photodynamic therapy. We compared the (photo)physical properties of polystyrene nanoparticles (TPP@PS) of different sizes and self-assembled poly(ethylene glycol)-b-poly(ε-caprolactone) core/shell nanoparticles (TPP@PEG-PCL) with different lengths of copolymer blocks, both suitable for the transport of the tetraphenylporphyrin photosensitizer (TPP). The singlet oxygen was formed inside both nanoparticles after irradiation with visible light. Its kinetics was controlled by the size of TPP@PS; its lifetime (τΔ) increased with increasing nanoparticle size (from 6.5 to 16 μs) due to hindered diffusion into the external aqueous environment, where it was quickly deactivated. Accordingly, the prolongation of the singlet oxygen-sensitized delayed fluorescence kinetics was found for TPP@PS of high size. The TPP@PEG-PCL self-assemblies allowed for enhanced oxygen diffusion, the estimated low values of τΔ ~ 3.7 μs were independent of the size of building blocks. The delayed fluorescence in oxygen-free conditions originating from triplet-triplet annihilation indicated a high mobility of TPP in the PCL core in comparison with fixed molecules in the PS matrix. Photooxidation of uric acid revealed the highest efficacy for TPP@PS of small sizes, whereas the largest TPP@PS exhibited the lowest activity, and the efficacy of TPP@PEG-PCL remained independent of the sizes of the building blocks.