Tunable Performance of Manganese Oxide Nanostructures as MRI Contrast Agents

The development of responsive magnetic resonance imaging contrast agents opens the door to a highly sensitive and specific diagnosis of altered physiological conditions. In this field, manganese dioxide (MnO₂ ) is starting to be a leading contributor due to its susceptibility to conditions relevant to human diseased states, such as cancer. So far, the preclinical application of MnO₂ has mainly been in the form of nanosheets, with enhancements of magnetic resonance imaging signals up to 50-fold upon activation. Herein, we thoroughly investigate, through a simple reaction, a series of Mn_x O_y samples and correlate their phase composition and structure/morphology to the performance as classic/responsive MRI contrast agents in response to redox changes. Signal enhancements as high as 140-fold were obtained from MnO₂ nano-urchins, and their capability as responsive magnetic resonance imaging contrast agents was demonstrated in vitro.