Synthesis of hollow and mesoporous structured NaYF4:Yb,Er upconversion luminescent nanoparticles for targeted drug delivery

In this paper, we demonstrated a one-step template-free strategy to fabricate a hollow mesoporous structured NaYF4:Yb,Er nanoparticles with excellent upconversion luminescence. Folic acid (FA), a commonly used cancer-targeting agent, was conjugated on the surface of the nanoparticles based on the presence of free amine groups, which were labeled as NaYF4:Yb,Er-FA HMUCNPs. The properties were extensively studied, which indicated the obtained samples showed a typical hollow mesoporous structure and excellent upconversion luminescence that were useful for cell imaging and drug delivery. The L929 cells viability, hemolysis assay and coagulation test demonstrated good biocompatibility of the samples. The anti-cancer drug doxorubicin hydrochloride (DOX) storage/release properties were demonstrated to be pH-responsive, in which, the drug release might be beneficial at the reduced pH for targeted release and controlled therapy. Moreover, it was found that DOX-loaded NaYF4:Yb,Er-FA HMUCNPs exhibited greater cytotoxicity to KB cells than free DOX due to the specific cell uptake by KB cells via folate receptor-mediate endocytosis. Therefore, the multifunctional nanoparticles combining upconversion luminescent property and hollow mesoporous structure have potential for simultaneous targeted anti-cancer drug delivery and cell imaging.