In situ modifications of porphyrin-conjugated magnetic nanoparticles for photodynamic inactivation of pathogens

The spread of infectious diseases is a consequence of environmental contamination due to the presence of pathogenic agents in aqueous media. Therefore, it is of a vital importance the development of an economical and eco-friendly method to eradicate these microorganisms. The use of photodynamic inactivation (PDI) with photosensitizers conjugated to magnetic nanoparticles (MNPs) has emerged as a successful approach for the rapid elimination of microorganisms. For this purpose, MNPs of Fe₃O ₄ coated with silica and terminal amine groups were synthetized. After that, 5,10,15,20tetrakis(pentafluorophenyl)porphyrin (TPPF₂₀) was covalently immobilized on the MNPs by nucleophilic aromatic substitution reaction. Then, the remaining pentafluorophenyl groups of attached to MNPs were substituted by polyethylenimine (PEI) or spermine (SP). Absorption and fluorescence emission spectra of these conjugates showed the typical bands of tetrapyrrolic macrocycles in water. On the other hand, photodynamic activity investigations indicated that these MNPs generated singlet molecular oxygen and superoxide anion radical in solution. In addition, PDI studies were carried out with Staphylococcus aureus and Escherichia coli. These MNPs were able to eradicate microorganisms (>6 log decrease) after 30 min of irradiation with white light. Therefore, the basic amine groups can be used to generate positive charges at physiological pH, which improve the interaction with the bacteria. Furthermore, this procedure facilitates the recycling and reuse of these MNPs after treatments using a magnetic field. These
results indicate that conjugates of TPPF₂₀ to MNPs are interesting photodynamic materials to eliminate pathogens.