Aqueous-stable Mn( <scp>ii</scp> )-MOF nanoparticles with high <i>r</i> ₁ relaxivity and biocompatibility: a novel <i>T</i> ₁ MRI contrast agent

The demand for safe, effective, and multifunctional magnetic resonance imaging (MRI) contrast agents (CAs) continues to drive the search for gadolinium-free alternatives. Here, we report the development of BVR-19-Mn, a novel, hydrolytically stable metal-organic framework (MOF) constructed from manganese (Mn(II)) and the amino acid L-cystine <i>via</i> a green, aqueous, room-temperature synthesis. BVR-19-Mn exhibits a high <i>r</i>₁ relaxivity of 4.98 mM^-1 s^-1 in water at 3 T and 25 °C, outperforming clinically approved gadolinium-based CAs such as Dotarem® under identical conditions. The enhanced relaxivity arises from a dense framework of Mn(II) centers, efficient water accessibility to internal pores, and favorable rotational dynamics inherent to its crystal structure. Importantly, BVR-19-Mn also demonstrates catalase-like activity, rapidly decomposing hydrogen peroxide into molecular oxygen, offering a mechanism to relieve tumor hypoxia. <i>In vitro</i> cytotoxicity and <i>in vivo</i> developmental zebrafish studies confirm biocompatibility across clinically relevant concentration ranges, with low toxicity observed at high dosing concentrations. Collectively, our findings position BVR-19-Mn as a high-performance MRI CA, introducing a sustainable, multifunctional platform for precision biomedical imaging.