Nanotechnology continuously explores new fields, and nanomedicine presents an entirely new research area with unlimited possibilities. For the last 20 years, gadolinium complexes have been used clinically as contrast enhancing agents for Magnetic Resonance Imaging (MRI). Simultaneously, Quantum Dots (QDs), with its excellent photostability and high quantum yield, are developed to replace organic fluorophores for medical diagnosis. The aim of this study is to develop nanoprobes that possess both the magnetic properties suitable for a contrast agent, and luminescent properties.

We have designed a novel nanomaterial of gadolinium oxide nanoparticles doped with europium (Eu:Gd₂O₃) or terbium (Tb:Gd₂O₃). Using nanoparticles, the local signal intensity in MRI can be increased compared to Gd complexes with only one Gd ion per complex. When introducing luminescent europium or terbium ions into the gadolinium oxide nanocrystal, fluorescent properties are added, creating a bifunctional nanocrystal. In addition to the favorable size for biomedical applications, nanoparticle contrast agents can bring advantages such as longer rotational correlation time to obtain increased relaxivity, and surface-coating possibilities for attaching targeting molecules. This will enable tailored design of a new generation of contrast agents. We present highly crystalline, 5 nm large nanoparticles, showing typical Eu³⁺ or Tb³⁺ fluorescence with a long luminescent lifetime. The strength of both europium and terbium ions is the suitable properties for excitation in an ordinary confocal microscope, which makes them promising as components when designing nanoprobes for cell studies. Relaxation measurements show relaxivity ratios in the same range as the pure Gd₂O₃ nanoparticles. The nanoparticles present a promising bifunctional core material, acting as a platform when developing advanced nanoprobes for future applications in biomedical imaging.