Nd³⁺sensitized dumbbell-like upconversion nanoparticles for photodynamic therapy application

Abstract

Better tissue penetration and lower overheating problems mean 808 nm near-infrared laser excited upconversion nanoparticles (UCNPs) have potential in bioapplications. Dumbbell-like structured NaYF₄:Yb/Er@NaNdF₄:Yb nanoparticles are fabricated in this work and applied in photodynamic therapy (PDT). The epitaxial growth along the c axis attributed to the large structure mismatch of NaNdF₄versus NaYF₄ has been demonstrated to play a key role in the growth of the dumbbell structure. Due to better space separation in this structure, energy back-transfer from Er³⁺ to Nd³⁺ is prohibited partially, and the optimized Nd³⁺ doping concentration is up to 90% for a high UC emission intensity. PDT effects of these dumbbell-like structured UCNPs upon 808 nm laser irradiation were examined and compared with isotropic NaYF₄:Yb/Er@NaYF₄:Nd_0.2 core-shell and NaYF₄:Yb/Er@NaYF₄:Nd_0.2@NaYF₄ core-shell-shell UCNPs. The results show that the dumbbell-like UCNPs are most effective in generating singlet oxygen (¹O₂) and killing cancer cells in PDT though their UC emission intensity is lower than that of the core-shell-shell UCNPs. This research presents a simple yet valid strategy to balance the UCL efficiency and FRET efficiency, which may lead to better PDT therapeutic effect for cancer therapy.