Encapsulation of Photosensitizers and Upconversion Nanocrystals in Lipid Micelles for Photodynamic Therapy

Photodynamic therapy (PDT) is a promising method for cancer therapy. However, it is constrained by limited penetration depth of visible light, hydrophobicity of photosensitizers, and lack of tumor targeting. In this work, the photosensitizer zinc phthalocyanine (ZnPc) and upconversion nanocrystals (UCNs) are encapsulated into OQPGA-PEG/RGD/TAT lipid micelles. The UCNs acting as a nanotransducer convert deep-penetrating near-infrared (NIR) light to visible light for activating the photosensitizer. OQPGA-PEG/RGD/TAT lipid micelles are used as a carrier for the photosensitizer, with improved biocompatibility and cancer-targeting ability. The results show that the photosensitizer ZnPc- and UCNs-loaded OQPGA-PEG/RGD/TAT lipid micelles are nanoparticles with an average size of 25 nm. The lipid micelle nanoparticles are stable in water with low leakage of photosensitizer. The absorption peak of the photosensitizer overlaps with the emission peak of UCNs, so the visible fluorescence emitted from the UCNs upon excitation by the NIR laser at 980 nm can activate the photosensitizer to produce singlet oxygen for PDT. The targeting RGD peptide and cell-penetrating TAT peptide on the surface help the nanoparticles getting into cancer cells. The OQPGA-PEG/RGD/TAT lipid micelles encapsulated with both the photosensitizer ZnPc and UCNs could be used for targeted PDT by using deep-penetrating NIR light as the light source.