Dual imaging probes for magnetic resonance imaging and fluorescence microscopy based on perovskite manganite nanoparticles

The present study reveals the potential of magnetic nanoparticles based on the La(0.75)Sr(0.25)MnO(3) perovskite manganite for magnetic resonance imaging (MRI). Moreover, it describes the development of the dual imaging probe where the magnetic cores are combined with a fluorescent moiety while the improved colloidal stability is achieved by a two-ply silica shell. At first, the magnetic cores of La(0.75)Sr(0.25)MnO(3) are coated with a hybrid silica layer, comprising a covalently attached fluorescein moiety that is subsequently covered by a pure silica layer providing the enhanced stability. The detailed characterization of the intermediate and the final product reveals the importance of the complex two-ply shell. Viability tests show that the complete particles are suitable for biological studies. Internalization of the particles and their presence in intracellular vesicles are observed by fluorescence microscopy in different cell types. Further experiments prove no fatal interference with the vitality and insulin releasing ability of labeled pancreatic islets. Relaxometric measurements confirm high spin-spin relaxivities at magnetic fields of B(0) = 0.5-3 T, while visualisation of in vitro labeled pancreatic islets by MRI is successfully tested.