YVO4:Eu3+ functionalized porous silica submicrospheres as delivery carriers of doxorubicin

Porous silica microspheres were fabricated by a facile surface-protected etching strategy. Polyvinylpyrrolidone (PVP) was used as a protecting polymer absorbed on the surface of silica microspheres and NaOH was employed as an etching agent. Owing to the protective action of PVP and inhomogeneous etching, mesopores were created in the silica microspheres. Then, based on the Pechini-type sol-gel and impregnating process, YVO4:Eu3+ nanocrystals were integrated into the channels to form highly luminescent YVO4:Eu3+@SiO2 composite microspheres. The biocompatibility tests on L929 fibroblast cells using MTT assay reveal low cytotoxicity of the system. Owing to the large interior space and electrostatic interaction, the porous microspheres show a relatively high loading capacity (438 mg DOX/YVO4:Eu3+@SiO2 g) and encapsulation efficiency (87.6%) for the anti-cancer drug doxorubicin hydrochloride (DOX). The drug release behavior and cytotoxic effect against human cervical carcinoma cells (HeLa cells) of the DOX-loaded YVO4:Eu3+@SiO2 carriers were investigated in vitro. It was found that the carriers present a highly pH-dependent drug release behavior due to electrostatic interaction between the silica surface and DOX molecules. The drug release rate became greater at low pH owing to the increased electrostatic repulsion. The DOX-loaded carriers demonstrate a similar or even greater anti-cancer activity with respect to the free DOX against HeLa cells. Furthermore, the PL intensity of the microspheres shows correlation with the cumulative release of DOX. These results suggest that the composite can potentially act as a multifunctional drug carrier system with luminescent tagging and pH-controlled release properties.