Multimodal bioimaging using a rare earth doped Gd₂O ₂S:Yb/Er phosphor with upconversion luminescence and magnetic resonance properties

While infrared upconversion imaging using halide nanoparticles is very common, the search for very efficient halide free upconverting phosphors is still lacking. In this article we report Gd₂O₂S:Yb/Er, YbHo, YbTm systems as very efficient alternative phosphors that show upconversion efficiency comparable to or even higher than those of existing halide phosphors. While the majority of rare earth dopants provide the necessary features for optical imaging, the paramagnetic Gd ion also contributes to the magnetic imaging, thereby resulting in a system with bimodal imaging features. Results from imaging of the nanoparticles together with aggregates of cultured cells have suggested that imaging of the particles in living animals may be possible. In vitro tests revealed no significant toxicity because no cell death was observed when the nanoparticles were in the presence of growing cells in culture. Measurement of the magnetization of the phosphor shows that the particles are strongly magnetic, thus making them suitable as an MRI agent.