Molecular-based contrast agents for magnetic resonance imaging (MRI) are often characterized by insufficient relaxivity, thus requiring the systemic injection of high doses to induce sufficient contrast enhancement at the target site. In this work, gadolinium oxide (Gd2O3) nanoplates are produced via a thermal decomposition method. The nanoplates have a core diameter varying from 2 to 22 nm, a thickness of 1 to 2 nm and are coated with either an oleic acid bilayer or an octylamine modified poly(acrylic acid) (PAA-OA) polymer layer. For the smaller nanoplates, longitudinal relaxivities (r1) of 7.96 and 47.2 (mM s)(-1) were measured at 1.41 T for the oleic acid bilayer and PAA-OA coating, respectively. These values moderately reduce as the size of the Gd2O3 nanoplates increases, and are always larger for the PAA-OA coating. Cytotoxicity studies on human dermal fibroblast cells documented no significant toxicity, with 100% cell viability preserved up to 250 μM for the PAA-OA coated Gd2O3 nanoplates. Given the 10 times increase in longitudinal relaxivity over the commercially available Gd-based molecular agents and the favorable toxicity profile, the 2 nm PAA-OA coated Gd2O3 nanoplates could represent a new class of highly effective T1 MRI contrast agents.

Millions of people a year receive magnetic resonance imaging (MRI) contrast agents for the diagnosis of conditions as diverse as fatty liver disease and cancer. Gadolinium chelates, which provide preferred T1 contrast, are the current standard but face an uncertain future due to increasing concerns about their nephrogenic toxicity as well as poor performance in high‐field MRI scanners. Gadolinium‐containing nanocrystals are interesting alternatives as they bypass the kidneys and can offer the possibility of both intracellular accumulation and active targeting. Nanocrystal contrast performance is notably limited, however, as their organic coatings block water from close interactions with surface Gadoliniums. Here, these steric barriers to water exchange are minimized through shape engineering of plate‐like nanocrystals that possess accessible Gadoliniums at their edges. Sulfonated surface polymers promote second‐sphere relaxation processes that contribute remarkable contrast even at the highest fields (r1 = 32.6 × 10−3 m Gd−1 s−1 at 9.4 T). These noncytotoxic materials release no detectable free Gadolinium even under mild acidic conditions. They preferentially accumulate in the liver of mice with a circulation half‐life 50% longer than commercial agents. These features allow these T1 MRI contrast agents to be applied for the first time to the ex vivo detection of nonalcoholic fatty liver disease in mice.

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