Incorporation of gallium-68 into the crystal structure of Prussian blue to form K⁶⁸Ga_{: X}Fe_{1- x}[Fe(CN)₆] nanoparticles: Toward a novel bimodal PET/MRI imaging agent

Similarity between the Ga⁺ ion and the Fe³⁺ ion allows for partial replacement of Fe³⁺ ions with Ga³⁺ ions in the Fe(iii) crystallographic positions in Prussian blue (PB) to form various solid solutions KGa_xFe_1-x[Fe(CN)₆] (0 < x < 1). Such solid solutions possess very high thermodynamic stability as expected from the parent PB structure. Consequently, a simple one-step ⁶⁸Ga-labeling method was developed for preparing a single-phase nanoparticulate bimodal PET/MRI imaging agent based on the PB structural platform. Unlike the typical ⁶⁸Ga-labelling reaction based on metal complexation, this novel chelator-free ⁶⁸Ga-labeling reaction was shown to be kinetically fast under the acidic conditions. The Ga³⁺ ion does not hydrolyze, and affords the ⁶⁸Ga-labelled PB nanoparticles, which are easy to purify and have extremely high stability against radionuclidic leaching in aqueous solution.