Artificial pheomelanin nanoparticles and their photo-sensitization properties.

Pheomelanin-type nanoparticles (PMNPs) were synthesized through a simple oxidative polymerization of 3,4-dihydroxyphenylalanine (DOPA) in the presence of cysteine by KMnO4. The synthesized PMNPs had a diameter of approximately 100nm, exhibited high dispersion stability in neutral water and various culture media and possessed similar morphology to naturally occurring pheomelanins. The efficiency of photoinduced generation of hydroxyl radicals from PMNPs was determined and related in vitro cell experiments that were carried out, with data being compared to those from eumelanin-type nanoparticles (EMNPs) and natural sepia melanin nanoparticles. Endocytosed PMNPs showed the highest phototoxicity (~50% viability) to UV-irradiated HeLa cells, confirming the direct relationship between phototoxic efficiency and the generation of hydroxyl radicals through the complex processes of the O2 sensitization.