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

In this work, we report a facile solution-phase synthesis of highly uniform and well-dispersed urchinlike 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 D-5(0) -> F-7(1, 2, 3, 4) of Eu3+, with D-5(0) -> F-7(1) 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.