Zoledronic acid-loaded HAp-SiO₂-CaMoO₄:Eu³⁺ with luminescent properties as a novel drug delivery system

CaMoO₄:Eu³⁺-functionalized hydroxyapatite-silica (HAp-SiO₂-CaMoO₄:Eu³⁺) core-shell nanocomposites were synthesized for the first time and evaluated as a multifunctional drug delivery and imaging platform. HAp-SiO₂ nanocomposites were prepared via a hydrothermal route and subsequently functionalized with a luminescent CaMoO₄:Eu³⁺ shell using the Pechini sol-gel method. Structural analyses confirmed the successful coexistence of HAp, SiO₂, and CaMoO₄:Eu³⁺ phases, while electron microscopy revealed spherical core-shell morphologies. Dynamic light scattering measurements showed average hydrodynamic particle sizes of approximately 1085 nm for HAp-SiO₂ and 1427 nm for HAp-SiO₂-CaMoO₄:Eu³⁺ nanocomposites, indicating particle clustering in aqueous media, which is consistent with the low surface charge of the particles. The Eu³⁺-doped shell exhibited a strong red emission centered at 615 nm, demonstrating suitability for luminescence-based imaging. Zoledronic acid (ZA) was efficiently loaded onto the nanocomposites under supercritical CO₂ conditions, providing high loading efficiency and sustained release behavior. In vitro release studies in phosphate-buffered saline (pH 7.4, 37 °C) followed the Korsmeyer-Peppas kinetic model (n = 0.83), indicating a non-Fickian diffusion mechanism. Cytotoxicity assays on Saos-2 osteosarcoma cells demonstrated that ZA-loaded nanocomposites exhibited enhanced antiproliferative activity, with an IC₅₀ value of 56.33 μM after 48 h. These results highlight the potential of HAp-SiO₂-CaMoO₄:Eu³⁺ nanocomposites as an integrated theranostic system for targeted bone cancer therapy. Overall, the results demonstrate that the proposed nanocomposite design successfully translates the intended theranostic concept into experimentally validated structural, optical, and biological performance.