Multilayered Upconversion Nanocomposites With Dual Photosensitizing Functions For Enhanced Photodynamic Therapy

Photodynamic therapy?PDT?is known as a promising anticancer strategy owing to its high selectivity and minimally invasive treatment as compared with radiotherapy and chemotherapy.Upon light radiation,photosensitizers are triggered to induce cytotoxic reactive oxygen species?ROS?,subsequently leading to direct destruction of tumor cells.The majority of conventional photosensitizers are excited by ultraviolet?UV?or visible light,which have limited penetration depth in tissues.It is known that near-infrared?NIR?light has deep tissue penetration compared to visible and UV light,so PDT could be effective for treatment of deep-buried tumors by using NIR excitation light.Upconversion nanoparticles?UCNPs?have the ability to convert NIR light to UV/visible light and activate photosensitizers to produce toxic ROS for killing cancer cells.However,further development of NIR responsive PDT has been largely constrained by several problems including the selection of appropriate photosensitizers and the efficient use of upconversion luminescence.In recent years,a large variety of organic molecules,such as Chlorin e6?Ce6?,rose bengal?RB?,and hypocrellin A?HA?,were used as photosensitizers and combined with upconversioin nanoparticles for bioimaging and PDT.However these photosenstizers typically have narrow absorption bands and small extinction coefficients,resulting in low energy transfer and PDT efficiencies.Conjugated polymers have been attracted considerable interest because of their unique advantages in biological applications,such as large extinction coefficients and tunable optical properties.Because of their high quantum efficiency,conjugated polymers can act as photosensitizers to generate singlet oxygen for cancer cells killing.In this study,we construct a multilayered upconversion nanoplatform with polymer and a photoinitiator as photosensitizers to efficiently use the UV and visible upconversion emissions in NIR-responsive PDT.The main research contents are as follows:1.The highly crystalline?-NaYF₄:Yb/Tm UCNPs with narrow size distributions was synthesized using a high temperature thermolysis method.To prepare hydrophilic NPs,surface-coated oleic acid molecules were removed by acid treatment to afford ligand-free nanoparticles for further experiments.After removing the surface-coated oleic acid molecules,the UCNPs were coated with a conjugated polymer for singlet oxygen generation by visible upconversion emission and apo-Transferrin-titanocene?Tf@Tc?for free radical generation by UV upconversion emission for cancer cells killing.This design takes advantage of the multi-peak upconversion luminescence to generate two types of ROS for enhanced PDT.The crystal structure,size,zeta potential,spectra,and fluorescence decay curves of nanocomposites were characterized.The obtained UCNPs were highly crystalline and hexagonal with narrow size distributions and good monodispersity.From the analysis of the spectra,the effective energy transfer from the UCNPs to the photosensitizers was confirmed,which offers a possibility to induce remarkable PDT efficiency.2.We evaluated the PDT efficiency and the biotoxicity of the prepared nanocomposites.In vitro cellular assays show the synergistic therapeutic effect of the conjugated polymer and Tc as photosensitizers.In vivo animal studies show that tumor growth is significantly inhibited in the mice receiving the theranostic platform and NIR irradiation?decreased to 35%at day 14?.Meanwhile,Hematoxylin and Eosin?H&E?stained tissue sections did not show noticeable damage,inflammatory lesions or necrosis in all the major organs of the mice from all groups 14 days after PDT treatment,confirming that the nanocomposites had good biocompatibility.This safe and effective multilayered upconversion nanoplatform can find potential applications in NIR-mediated anti-tumor therapy.