Biotin-functionalized chitosan-based polyelectrolyte complex for encapsulation and photodynamic modulation of zinc(II) phthalocyanine.

This work reports the design and characterization of a polyelectrolyte complex (PEC) tailored for the encapsulation of zinc phthalocyanine (ZnPc) in its disaggregated form, aiming at photodynamic applications. The PEC was formed through the interaction between biotin-functionalized N,N,N-trimethyl chitosan (Bio-TMC) and a partially alkylated poly(imidazole-co-acrylate) (PAIm-12), both of which had been previously synthesized and structurally confirmed. The resulting ZnPc-PEC nanostructures exhibited an average hydrodynamic diameter of ∼100 nm and a positive surface charge (+29.2 mV), indicating enhanced colloidal stability compared to PAIm-12 aggregates (∼344 nm, +10.3 mV). FTIR analysis revealed axial coordination between the Zn center of ZnPc and the carboxylate groups of PAIm-12, an interaction that significantly influenced the photophysical response of the photosensitizer. Spectroscopic measurements confirmed that ZnPc remained predominantly disaggregated at 5 μmol L-1, retaining its characteristic absorption and emission features. Nonetheless, the PEC environment induced marked changes in the excited-state properties, including a reduced Stokes shift and a threefold decrease in fluorescence quantum yield, while fluorescence lifetime remained unaffected. The photochemical profile was also modulated, with ROS generation shifting from singlet oxygen in ethanol to a higher contribution of radical species, such as hydroxyl radicals, in the PEC matrix, as verified by selective quenching assays. Finally, ZnPc-PEC demonstrated effective photodynamic activity against B16F10 melanoma cells. Overall, these findings highlight how the PEC environment not only enhances the solubility of ZnPc but also governs its photophysical and photochemical pathways, providing a versatile supramolecular platform for photodynamic therapy and other biomedical applications that require controlled ROS generation.