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Manganese‐based nanostructured contrast agents (CAs) entered the field of medical diagnosis through magnetic resonance imaging (MRI) some years ago. Although some of these Mn‐based CAs behave as classic T1 contrast enhancers in the same way as clinical Gd‐based molecules do, a new type of Mn nanomaterials have been developed to improve MRI sensitivity and potentially gather new functional information from tissues by using traditional T1 contrast enhanced MRI. These nanomaterials have been designed to respond to biological environments, mainly to pH and redox potential variations. In many cases, the differences in signal generation in these responsive Mn‐based nanostructures come from intrinsic changes in the magnetic properties of Mn cations depending on their oxidation state. In other cases, no changes in the nature of Mn take place, but rather the nanomaterial as a whole responds to the change in the environment through different mechanisms, including changes in integrity and hydration state. This review focusses on the chemistry and MR performance of these responsive Mn‐based nanomaterials. Turn on, tune in: Manganese‐based nanostructured contrast agents (CAs) entered the field of medical diagnosis through magnetic resonance imaging (MRI) some years ago. Recently, a new type of Mn nanomaterials have been developed, which are designed to respond to biological environments (mainly pH and redox potential variations), to improve MRI sensitivity and potentially gather new functional information from tissues by using traditional T1 contrast enhanced MRI. [ABSTRACT FROM AUTHOR]

Abstract: 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 MnxOy 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. [ABSTRACT FROM AUTHOR]