Green-emitting lanthanum niobate mesoporous nanospheroids for near-infrared light responsive cancer theranostics

Biomedical applications require nonlinear optical materials with high performance and specific morphology. Among these materials, rare-earth niobates are very promising candidates. However, synthesizing pure-phase rare-earth niobates with controlled shape is challenging. To overcome this obstacle, we present a feasible technique to prepare biocompatible LaNbO₄:Er³⁺/Yb³⁺ mesoporous nanospheroids with strong upconversion luminescence. We use a pre-Ouzo effect assisted hydrothermal process to obtain the monoclinic phase nanospheroids, which exhibit two-photon excitation induced green emission under 980 nm laser irradiation. We also investigate the energy transfer mechanism between Yb³⁺ and Er³⁺ in the LaNbO₄ matrix and also explored their pathways in energy level diagram. The cytocompatibility of the LaNbO₄:Er³⁺/Yb³⁺ mesoporous nanospheroids is verified by Cell Counting Kit-8 assay. Moreover, the cytoplasm and nucleoplasm of LaNbO₄:Er³⁺/Yb³⁺ mesoporous nanospheroids stained MDA-MB-231 breast cancer cells exhibit upconversion luminescence, indicating that the mesoporous nanospheroids can enter them effectively. Additionally, these nanospheroids have a good ability to deliver DOX to the cancer cells. These results suggest that the LaNbO₄:Er³⁺/Yb³⁺ mesoporous nanospheroids are promising candidates for luminescence imaging-based cancer diagnosis and therapy.