Inorganic photosensitizer coupled Gd-based upconversion luminescent nanocomposites for in vivo magnetic resonance imaging and near-infrared-responsive photodynamic therapy in cancers

Inorganic photosensitizer coupled Gd-based upconversion luminescent (UCL) nanocomposites have potential application for both magnetic resonance imaging (MRI) and photodynamic therapy (PDT) of cancers using the light stability and biocompatibility of TiO 2 inorganic photosensitizer. However, TiO 2 inorganic photosensitizer could only be excited by ultraviolet (UV) light, which was harmful and weakly penetrable in tissues. In this work, folic acid (FA)-targeted NaGdF 4 :Yb/Tm@SiO 2 @TiO 2 nanocomposites (FA-Gd-Si-Ti NPs) were constructed and synthesized for both in vivo MRI and near infrared (NIR)-responsive inorganic PDT, in which TiO 2 component could be excited by NIR light due to the UCL performance of NaGdF 4 :Yb/Tm component converting NIR to UV light. The results showed the as-prepared FA-Gd-Si-Ti NPs had good biocompatibility in vitro and in vivo. Moreover, MR study indicated that FA-Gd-Si-Ti NPs were good T 1 -weighted MRI contrast agents with high longitudinal relaxivity (r 1 ) of 4.53 m m −1  s −1 , also in vivo MRI of nude mice showed “bright” signal in MCF-7 tumor. Under the irradiation of 980 nm laser at the power density of 0.6 W/cm 2 for 20 min, the viability of HeLa and MCF-7 cells incubated with FA-Gd-Si-Ti NPs could decrease from about 90 % to 35 % and 31%, respectively. Furthermore, in vivo PDT of MCF-7 tumor-bearing nude mice model showed that the inhibition ratio of tumors injected with FA-Gd-Si-Ti NPs reached up to 88.6% after 2-week treatment, compared with that of nude mice in control group. Based on the deep penetration of NIR light and the good biocompatibility of TiO 2 inorganic photosensitizer, the as-prepared FA-Gd-Si-Ti NPs could have potential applications in both MRI and NIR-responsive PDT of cancers in deep tissues.