Synthesis of ⁶⁸Ga Core-doped Iron Oxide Nanoparticles for Dual Positron Emission Tomography /(T₁)Magnetic Resonance Imaging

Here, we describe a microwave synthesis to obtain iron oxide nanoparticles core-doped with ⁶⁸Ga. Microwave technology enables fast and reproducible synthetic procedures. In this case, starting from FeCl₃ and citrate trisodium salt, iron oxide nanoparticles coated with citric acid are obtained in 10 min in the microwave. These nanoparticles present a small core size of 4.2 ± 1.1 nm and a hydrodynamic size of 7.5 ± 2.1 nm. Moreover, they have a high longitudinal relaxivity (r₁) value of 11.9 mM^-1·s^-1 and a modest transversal relaxivity value (r₂) of 22.9 mM^-1·s^-1, which results in a low r₂/r₁ ratio of 1.9. These values enable positive contrast generation in magnetic resonance imaging (MRI) instead of negative contrast, commonly used with iron oxide nanoparticles. In addition, if a ⁶⁸GaCl₃ elution from a ⁶⁸Ge/⁶⁸Ga generator is added to the starting materials, a nano-radiotracer doped with ⁶⁸Ga is obtained. The product is obtained with a high radiolabeling yield (> 90%), regardless of the initial activity used. Furthermore, a single purification step renders the nano-radiomaterial ready to be used in vivo.