Calcium phosphate nanoparticles as efficient carriers for photodynamic therapy against cells and bacteria

Calcium phosphate nanoparticles were surface-functionalized with different polymers, and photosensitizers were incorporated into this layer. The charge was adjusted by choosing the appropriate polymer. Methylene blue and 5,10,15,20-tetrakis(3-hydroxyphenyl)porphyrin (mTHPP) were used as photosensitizers. The particles showed a good performance with HIG-82 synoviocytes. For J774A.1 macrophages, they were toxic also in the dark, probably due to a lethal uptake of calcium. For HT29 epithelial cells, a moderate activity was observed. A good photoxicity was observed against the bacterial strain Staphylococcus aureus (Gram-positive), both with positively and negatively charged nanoparticles loaded with mTHPP. Against Pseudomonas aeruginosa (Gram-negative), good photoxicity was observed only with positively charged nanoparticles loaded with mTHPP. At higher concentrations, methylene blue-loaded nanoparticles were active against S. aureus. Thus, it is possible to prepare a water-dispersable system of dye-loaded calcium phosphate nanoparticles, but the efficiency depends on a number of parameters, e.g. particle charge, kind of polymer, and cell culture medium (e.g. the presence of proteins).