Facile one-pot synthesis of hollow mesoporous fluorescent Gd2O3:Eu/calcium phosphate nanospheres for simultaneous dual-modal imaging and pH-responsive drug delivery

The hollow nanospheres (NSs) composed of lanthanides have become a hot topic owing to their uncommon magnetic and optical properties arising from the 4f electrons. However, only a few novel methods have been developed for effectively integrating small calcium phosphate (CaP) nanoparticles and rare earth oxide drug carriers into an individual hollow mesoporous nanosphere. Herein, we report a facile, reproducible, room-temperature solution method to prepare multifunctional fluorescent hollow mesoporous Gd 2 O 3 :Eu/CaP (designated as HM-Gd 2 O 3 :Eu/CaP) NSs by using polyacrylic acid calcium (PAA-Ca) as a template. The excellent luminescent property and obvious T 1 -enhancement effect as well as the HM structure endow the HM-Gd 2 O 3 :Eu/CaP NSs with the capacity of simultaneous dual-modal fluorescence, magnetic resonance (MR) imaging and drug delivery. The nanocontainer-functionality of the HM-Gd 2 O 3 :Eu/CaP NSs is further validated upon filling with the anti-cancerogenic agent doxorubicin (drug-loading capacity is 749 μg mg −1 ). In addition, the HM-Gd 2 O 3 :Eu/CaP NSs display excellent pH-responsive and sustained drug release property. In vitro cell cytotoxicity tests verify the HM-Gd 2 O 3 :Eu/CaP NSs have good biocompatibility when the concentration ≤25 mg mL −1 . Taken together, the results suggested that the HM-Gd 2 O 3 :Eu/CaP NSs can be applied as fluorescence and MR dual-modal imaging contrast agents and drug delivery vehicles.