Methylene blue functionalized ZnO nanoparticles: A promising approach for photodynamic therapy in the treatment of leishmaniasis

Zinc oxide (ZnO) has wide application in engineering, but its use in medical sciences has aroused growing interest. In this context, ZnO nanoparticles were investigated as vehicles for the delivery of methylene blue (MB), a photosensitizer (PS) used in photodynamic therapy (PDT) against <i>Leishmania braziliensis</i>. ZnO-NPs were produced by a coprecipitation method and characterized by several techniques, including scanning electron microscopy (SEM), UV-VIS spectroscopy, Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The results showed that the ZnO-NPs presented uniform spheroidal morphology with open porosity, allowing an efficient methylene blue (MB) encapsulation without significant structural changes, ensuring stability and the absence of aggregation. The PS was adsorbed on the porous surface of the ZnO nanoparticles, characterized by scanning electron microscopy (SEM) and steady-state analysis techniques. Spectroscopic analysis confirmed the maintenance of the photosensitizing properties of MB. The biological activity was evaluated in vitro using the trypan blue exclusion method in macrophages infected with <i>Leishmania braziliensis</i>. After loading with the photosensitizer, they maintained their photophysical properties, ensuring the proper location of the dye within the cells. In vitro assays demonstrated the internalization of ZnO/MB-NPs by infected macrophages and a significant reduction in parasite viability after light activation. Thus, the results showed that the developed system exhibits a promising photodynamic activity with relevant therapeutic potential in treating macrophages infected by <i>Leishmania braziliensis</i>.