Controllable synthesis of up-conversion nanoparticles UCNPs@MIL-PEG for pH-responsive drug delivery and potential up-conversion luminescence/magnetic resonance dual-mode imaging

Abstract Rare-earth doped up-conversion nanoparticles (UCNPs) with high uniformity and dispersibility were synthesized by a facile solvothermal method. The conditions of synthesis for NaYF4:Yb/Tm were explored, and the NaYF4:Yb/Tm particles with the optimal size (about 300 nm) were obtained. Blue emission was observed with the excitation 980 nm near infrared (NIR) laser, indicating that the UCNPs can be potentially used for up-conversion luminescence (UCL) imaging. On basis of the optimal UCNPs, further coated by poly (ethylene glycol) (PEG) functionalized metal-organic frameworks (MOFs), a multifunctional platform UCNPs@MIL-PEG for cancer diagnosis and treatment was established. The core-shell structure was confirmed by TEM images. Doxorubicin (DOX) was selected as drug model and the drug loading of UCNPs@MIL-PEG was found to be 60%. Cytotoxicity indicated that UCNPs@MIL-PEG were highly biocompatible. The DOX release in different pH value revealed an excellent pH-triggered drug release. In addition, the UCNPs@MIL-PEG nanoparticles can be tracked by magnetic resonance imaging (MRI). A clear dose-dependent contrast enhancement in T2-weighted MR images indicated the potential act as T2 MRI contrast agents. The UCNPs@MIL-PEG nanoparticles are expected to be simultaneously used for UCL/MR dual-mode imaging and pH-responsive drug release.