Pre-ouzo effect derived fergusonite gadolinium ortho-niobate mesoporous nanospheroids for multimodal bioimaging and photodynamic therapy

Rare-earth niobate compounds are excellent nonlinear optical materials. Unlike other niobate materials, gadolinium ortho-niobate (GdNbO₄) is reported to be inert in the visible region. The synthesis of pure-phase GdNbO₄ with a definite morphology suitable for biomedical applications is still a great challenge. In this study, a novel strategy is introduced to successfully facilitate the bioavailability of GdNbO₄:Eu³⁺ luminescent material by harnessing the pre-ouzo effect during the synthesis of mesoporous GdNbO₄:Eu³⁺ nanospheroids. Because of the materialization of GdNbO₄ nanodomains, the mesoporous GdNbO₄ nanospheroids exhibit paramagnetic behaviour and allows the strong broadband excitation between 300 and 500 nm, which permits NbO₆ emissions to be obtained in the visible region, whereas Eu³⁺ activated mesoporous GdNbO₄ nanospheroids produce an intense red emission under UV, near-UV and visible excitations. These mesoporous nanospheroids also demonstrate excellent cellular internalization for HCT116 and SW680 colon cancer cells and work in conjunction with optical and magnetic resonance imaging for the accurate diagnosis and prognosis of anatomical and physiological functions. The conjugation of chlorin e6 with mesoporous GdNbO₄:Eu³⁺ nanospheroids leads to efficient photodynamic therapy (PDT) in cancer treatment. Ultimately, our approach represents an advance in the use of mesoporous GdNbO₄:Eu³⁺ nanospheroids as multifunctional nanoprobes for multimodal imaging and PDT.