Encapsulation of a Hydrophobic Fluorenyl‐Porphyrin in Biocompatible Nanoparticles: Influence of Photosensitizer Loadings on Two‐Photon Phototherapeutic Potential

The synthesis of a new star‐shaped hydrophobic porphyrin photosensitizer ( PS ), decorated with four strong two‐photon absorbing antennae is reported. This compound, acting as a powerful fluorescent two‐photon PS in organic solvents, is encapsulated at various loadings into biocompatible poly(benzyl malate)‐based polymeric nanoparticles (NPs). The resulting formulations are characterized in terms of NPs size and dispersity. Herein, it is shown that stable monodisperse formulations can be obtained up to 25 wt% loadings (relative to polymer mass). Given that the highest loading are desirable in therapy, the influence of porphyrin loading on the one‐ and two‐photon photophysical properties of the NPs in water is subsequently investigated. While fluorescence is not significantly affected by increasing loadings, the singlet oxygen quantum yield decreases at higher loadings together with the two‐photon absorption (2 PA) cross‐section ( σ 2 ) values. However, the 2 PA capacity of PS at 25 wt% loading remained competitive, keeping the same order of magnitude than at lower loadings. Finally, to evaluate how loading affects two‐photon phototherapy and fluorescence imaging, the performances of the NPs are evaluated through in vitro studies on MCF‐7 breast cancer cells. Despite the strong confinement experienced in situ by the PS , the better results were obtained with the most highly loaded NPs (25 wt%) validating a posteriori the potential of these nanoobjects for theranostic applications.