MnO Nanoparticles Embedded in Functional Polymers as T₁ Contrast Agents for Magnetic Resonance Imaging

The design and development of contrast agents (CAs) for magnetic resonance imaging (MRI) in clinical analysis is expected to improve image spatial resolution and to increase detection sensitivity, especially regarding neurological disorders and cancer disease. In particular, advanced CAs for T1-weighted images are investigated to achieve sensitive detection of early stage primary tumors or brain metastases. In this study, we present a strategy toward diagnostic T1 contrast agents for MRI, based on polymer-modified MnO nanoparticles. Two different nanosystems were synthesized, consisting of 1) colloidal MnO nanocrystals wrapped by a multidentate amphiphilic polymer, and 2) MnO nanocrystals embedded into PLGA nanoparticles. These nanosystems were compared in terms of their MRI contrast power and biological safety. The latter combines the excellent biocompatibility of PLGA with the unique magnetic properties of MnO nanoparticles and allows sustained contrast enhancement over time. Longitudinal relaxivities of both MnO composite nanomaterials proved to be higher than those of commercial Gd-based contrast agents and Teslascan©, both in phosphate buffer saline and in plasma, also exhibiting low cytotoxicity. The high relaxation rates achieved with these contrast enhancers are promising toward future application in in vivo imaging.