Photosensitizer coated upconversion nanoparticles for triggering reactive oxygen species under 980 nm near-infrared excitation

Abstract

Rare-earth-based upconversion nanotechnology has recently shown great promise for photodynamic therapy (PDT). NaGd(MoO₄)₂-based materials have a scheelite structure with good thermal and chemical stability, and excellent up-conversion luminescence properties after co-doping rare earth ions (Tm³⁺ and Yb³⁺), which can effectively excite the photosensitizer to generate reactive oxygen species (ROS). In this work, Tm³⁺ and Yb³⁺ co-doped NaGd(MoO₄)₂ upconversion nanoparticles (UCNPs) are prepared by the sol–gel method and further complexed with photosensitizer MC540 (UCNPs@MC540). The prepared UCNPs showed a tetragonal phase and revealed nanoparticles with an average size of 150 nm. Under 980 nm excitation, the UCNPs exhibited a dominant blue emission band (¹G₄ → ³H₆) of Tm³⁺, while the optimum doping concentration was identified at 1% Tm³⁺ and 20% Yb³⁺. In addition, the blue emissions of Tm³⁺ simultaneously activate the MC540 composited on the surface of the nanoparticles to produce a large amount of singlet oxygen (¹O₂), which is detected by DCFH-DA. Moreover, UCNPs@MC540 also shows strong emission at around 800 nm near-infrared. The results show that the UCNPs@MC540 materials have potential application prospects in PDT and biological imaging.