Preparation and iodine labeling properties of nanophotosensitizer NaYF<sub>4</sub>:Yb,Tm@NaGdF<sub>4</sub>:Yb@SiO<sub>2</sub>@TiO<sub>2</sub>-Au

Abstract

Photodynamic therapy (PDT) is a promising therapeutic method for cancer due to many advantages including non-invasion, highly localized tissue region, low toxicity, and insignificant side effects. However, the poor tissue penetration of visible light for activating the traditional photosensitizer confines the utilization of PDT in the treatment of tumors embedded in thick biotissues. Upconversion nanoparticles (UCNPs) can be used to fabricate near-infrared light-triggered nanophotosensitizers by loading organic dyes or coating with inorganic semiconductor nanocrystals such as TiO2 and ZnO for deep-tissue PDT. In addition, some UCNPs-based nanophotosensitizers exhibit remarkable imaging properties for tumor detection. Improvement in reactive oxygen species (ROS) production and imaging sensitivity is the prerequisite for the application of UCNPs-based nanophotosensitizers in cancer diagnosis and therapy. Here, a near-infrared light-driven nanophotosensitizer UST-Au was prepared by assembling Au nanoparticles (AuNPs) on the surface of polyethyleneimine-modified NaYF4:Yb,Tm@NaGdF4:Yb@SiO2@TiO2 nanocomposites (UST), and then labeled with radioactive iodine ions (131I−) by virtue of Au-I− affinity interaction. The effects of AuNPs dosage on the morphology, diameter, zeta potential, optical properties, ROS generating ability and iodine labeling performance of the product were studied. And the feasibility of 131I−-labeled UST-Au as a single photon emission computed tomography (SPECT) imaging probe was analyzed. The results showed that tunable amounts of AuNPs were immobilized on the surface of polyethyleneimine-coated UST and the obtained UST-Au produced more ROS than UST as exposed to 980 nm near-infrared light. As AuNPs was added to be 3 wt% of the mass of UST, the obtained nanophotosensitizer had a mean hydrodynamic diameter (258 nm), relatively high zeta potential (+22.4 mV), good colloidal stability and the optimal ROS generation ability. Unexceptionally, iodine ions were expeditiously labeled on UST-Au suspended in aqueous solution, and the amount of the bound iodine ions enhanced with the increase of the mass percent of Au in UST-Au. The radiolabeling yield of UST-Au-131I− was more than 95%. Furthermore, the iodine labeling reaction had negligibly negative effect on the colloidal stability and ROS production of the nanophotosensitizer. In general, all these unique properties of the nanophotosensitizer facilitate the potential application in SPECT imaging-guided photodynamic therapy against tumor.