ZnO:Er,Yb,Gd Particles Designed for Magnetic-Fluorescent Imaging and Near-Infrared Light Triggered Photodynamic Therapy

Abstract

In this paper, fluorescent and magnetic bifunctional ZnO:Er,Yb,Gd particles were synthesized via a simple homogeneous precipitation method. The morphology, size, fluorescent properties, and magnetic properties of the particles can be readily modified by doping with Er³⁺, Yb³⁺, and Gd³⁺. The results revealed that the ZnO:Er,Yb,Gd particles have both down-conversion and up-conversion fluorescence after calcination at high temperatures (>700 °C). The products successfully labled the human hepatocellular carcinoma (HepG2) cells and presented low toxicity even at a high concentration of 2 mg/mL. Being upconverting nanoparticles (UCNPs), the prepared ZnO:Er,Yb,Gd particles exposed to 980 nm near-infrared (NIR) laser light emitted up-conversion fluorescence which could be absorbed by a photodynamic therapy (PDT) drug, methylene blue (MB), and then killed the HepG2 cells via PDT mechanism. In vitro therapeutic investigation evidenced the prominent PDT effects of MB-loaded ZnO:Er,Yb,Gd UCNPs upon NIR light irradiation. In magnetic resonance imaging (MRI) studies, ZnO:Er,Yb,Gd particles revealed a tunable longitudinal relaxivity rate (<i>r</i>₁) from 23.03 mM^–1s^–1 to 36.84 mM^–1 s^–1, which is much larger than the conventional Gd-DTPA and currently reported Gd-base nanoparticles, suggesting it would be a good candidate as an MRI agent. It is expected that these particles have applications in magnetic-fluorescent bimodal imaging and NIR light triggered photodynamic therapy