Bifunctional Pyrrolidin-2-one Terminated Manganese Oxide Nanoparticles for Combined Magnetic Resonance and Fluorescence Imaging

Multimodal probes are an asset for simplified, improved medical imaging. In particular, fluorescence and magnetic resonance imaging (MM) are sought-after combined capabilities. Here, we show that pyrrolidin-2-one-capped manganese oxide nanoparticles (MnOPyrr NPs) combine MM with fluorescence microscopy to function as efficient bifunctional bio-nanoprobes. We employ a one-pot synthesis for ca. 10 nm MnO NPs, wherein manganese(II) 2,4-pentadionate is thermally decomposed using pyrrolidin-2-one as a solvent and capping ligand. The MnOPyrr NPs are soluble in water without any further postsynthetic modifications. The r(1) relaxivity and r(2)/r(1) ratio indicate that these NPs are potential T-1 MRI contrast agents at clinical (3 T) and ultrahigh (9.4 T) magnetic fields. Serendipitously, the as-prepared NPs are photoluminescent. The unexpected luminescence is ascribed to the modification of the pyrrolidin-2-one during the thermal treatment. MnOPyrr NPs are successfully used to enable fluorescence microscopy of HeLa cells, demonstrating bifunctional imaging capabilities. A low cytotoxic response in two distinct cell types (HeLa, HepG2) supports the suitability of MnOPyrr NPs for biological imaging applications.