Core–Shell Structured NaYF4:Yb,Er Nanoparticles with Excellent Upconversion Luminescent for Targeted Drug Delivery

A core–shell-structured composite by combining mesoporous silica with upconversion luminescence (UCL) property had considerable application potentials in the fields of drug delivery, disease diagnosis, and therapy. In this paper, a monodisperse, core–shell-structured NaYF 4 :Yb,Er@ n SiO 2 @ m SiO 2 nanoparticle (UCNP@MSNs-FA) with excellent UCL property was successfully fabricated by a facile two-step sol–gel strategy and by modifying the surface with folic acid (FA) to strengthen its tumor-targeting performance. The properties of the composite were studied extensively, which indicated that UCNP@MSNs-FA possessed good dispersion, typical core–shell-structured with high specific surface area (132.775 m 2 /g), and excellent UCL property that improve cell imaging and drug delivery. The viability of L929 cells and hemolysis assay demonstrated the good biocompatibility of the composite. By using doxorubicin hydrochloride (DOX) as a model drug, the drug loading content and encapsulation efficiency of UCNP@MSNs-FA could reach as high as 11.2% and 37.3%, respectively, which proved the effectiveness to load anticancer drugs. In addition, the DOX-UCNP@MSNs-FA system exhibited sustained drug release and strong pH-dependent performance, in which the drug release would be accelerated at the slightly acidic microenvironment in the tumor. Moreover, experimental results indicated that DOX-UCNP@MSNs-FA exhibited specific cytotoxicity to KB cells but weakened toxicity to FR-negative cells. Therefore, the as-prepared UCNP@MSNs-FA could be used potential for simultaneous targeted anti-cancer drug delivery and cell imaging and enhance the therapeutic efficacy against FR-positive tumor cells.