Urchin-like GdPO4 and GdPO4:Eu3+ hollow spheres – hydrothermal synthesis, luminescence and drug-delivery properties

Abstract

In this work, we report a facile solution-phase synthesis of highly uniform and well-dispersed urchin-like GdPO₄ hollow spheres (around 250 nm) by utilizing the colloidal spheres of Gd(OH)CO₃ as a sacrificial template and NH₄H₂PO₄ as a phosphorus source. Monodisperse urchin-like GdPO₄ hollow spheres with controlled size were synthesized through the Kirkendall effect via the hydrothermal process. Nitrogen adsorption–desorption measurements suggest the presence of mesopores (av. 18.8 nm) in these hollow spheres. In addition, Eu³⁺-doped GdPO₄ hollow spheres exhibit strong orange-red emission, corresponding to the characteristic transitions of ⁵D₀ → ⁷F_{1, 2, 3, 4} of Eu³⁺, with ⁵D₀ → ⁷F₁ transition as the most prominent group. Attempts were made to utilize the luminescent GdPO₄:Eu³⁺ hollow spheres as drug carriers. The biocompatibility test on L929 fibroblast cells using MTT assay reveals low cytotoxicity of the system. An Ibuprofen-loaded GdPO₄:Eu³⁺ sample still shows orange–red luminescence of Eu³⁺ under UV irradiation, and the emission intensity of Eu³⁺ in the drug-carrier system varies with the released amount of ibuprofen, so that the drug together with its release situation can be easily tracked and monitored by the change in luminescence intensity.