Photodynamic inactivation (PDI) has emerged as an effective and selective strategy for microbial inactivation, where close contact between microorganisms and the photosensitizer (PS) is essential to ensure its efficacy. Achieving proper dispersion of the PS in aqueous media is crucial for its performance. In this work, magnetic nanoparticles (MNPs) were designed as platforms to transport PSs in aqueous environments.

Iron oxide (Fe₃O₄) MNPs were synthesized using the conventional co-precipitation method. FeCl₂·4H₂O and FeCl₃·6H₂O were dissolved in water and reacted under mild conditions. The resulting MNPs were then coated with metasilicate, incorporating Na₂SiO₃·5H₂O, to provide colloidal stability. The obtained MNPs-SiO₂ was washed by magnetic decantation and functionalized with aminopropyltriethoxysilane (APTES) in a toluene/THF (1:1) mixture. This spacer introduced aliphatic amine groups capable of reacting through nucleophilic aromatic substitution (S_NAr) with the PSs. Finally, the MNPs-SiO₂-NH₂ was suspended in DMF to react with 5,10,15,20-tetrakis(pentafluorophenyl)chlorin (TPCF₂₀) and its Zn(II) complex (ZnTPCF₂₀). This covalent coupling allowed for the preparation of MNPs-TPCF₂₀ and MNPs-ZnTPCF₂₀, which remained stable in aqueous solutions. Moreover, the magnetic nature of the MNPs-PS facilitated their removal from the medium using external magnetic fields. Spectroscopic characterizations confirmed the retention of the photophysical properties of the attached chlorins. The materials showed the ability to generate reactive oxygen species (ROS) and photodynamic efficacy against both Gram-positive and Gram-negative microorganisms. These results highlight the potential of chlorin-functionalized magnetic nanoparticles as effective antimicrobial agents for applications in aqueous environments.