Magnetic-luminescent YbPO4:Er,Dy microspheres designed for tumor theranostics with synergistic effect of photodynamic therapy and chemotherapy

In this paper, magnetic and fluorescent bifunctional YbPO4:Er,Dy microspheres were synthesized via a simple solvothermal method. The prepared microspheres exposed to 980 nm near-infrared (NIR) laser light emitted bright upconversion fluorescence (450-570 nm) after calcination at high temperatures (>800°C). Results of magnetic resonance studies demonstrated that the YbPO4:Er,Dy microspheres are more suitable to be used as a transverse relaxation time (negative) contrast magnetic resonance imaging agent. The microspheres successfully entered the human hepatocellular carcinoma cells and presented low toxicity. A well-selected photodynamic therapy (PDT) drug, merocyanine 540 (MC540) with an ultraviolet-visible spectroscopy absorption maximum of 540 nm, was loaded onto the microspheres to obtain YbPO4:Er,Dy-MC540. Since the upconversion fluorescence emitting from the microspheres could be absorbed by MC540 with a small absorption/emission disparity, YbPO4:Er,Dy-MC540 could kill the hepatocellular carcinoma cells via PDT mechanism effectively. In other words, being upconverting particles, the prepared microspheres acted as light transducers in the NIR light-triggered PDT process. A chemotherapy drug, doxorubicin, was further loaded onto YbPO4:Er,Dy-MC540 to achieve enhanced antitumor effect based on synergistic therapeutic efficacy of PDT and chemotherapy. It is expected that the prepared YbPO4:Er,Dy microspheres have applications in tumor theranostics including magnetic-fluorescent bimodal imaging and NIR light-triggered PDT.