Enhancement of the photokilling effect of aluminum phthalocyanine in photodynamic therapy by conjugating with nitrogen-doped TiO2 nanoparticles.

As a second-generation photodynamic therapy (PDT) photosensitizer, aluminum phthalocyanine chloride tetrasulfonate (Pc) has gained great attention due to its high absorption at the red light region. Yet, its application in PDT is strongly limited by its low cellular uptake efficiency. In this report, nitrogen-doped TiO2 nanoparticles (N-TiO2) conjugated with Pc are synthesized by a two-step surface modification method. The N-TiO2-Pc products are characterized by Zeta potential, transmission electron microscopy and UV-vis absorption spectroscopy. The cellular uptake, intracellular distribution, cytotoxicity and the photokilling effect of the nanoparticles are studied on different cancer cell lines. Compared with Pc, the absorption spectrum of N-TiO2-Pc expands from red to UV region, resulting in a higher production of reactive oxygen species under visible light irradiation. In addition, the cellular uptake of Pc is largely improved by its carrier N-TiO2. The photokilling efficiency of N-TiO2-Pc is over ten times higher than that of Pc. The results suggest that N-TiO2-Pc is an excellent candidate as a photosensitizer in PDT.