Water‐Dispersible Metal Oxide Nanoparticles Synthesized Via Hydrogen‐Bond‐Mediated Aqueous Solution: Gd ₂ O ₃ for High‐Performance T1 Magnetic Resonance Imaging Contrast Agent

Superior aqueous dispersibility mitigates nanoparticle toxicity in biological systems while preventing agglomeration. Herein, a hydrogen-bond-mediated aqueous synthesis strategy is proposed, utilizing β-cyclodextrin (β-CD) and sodium citrate (SC) to directly fabricate metal oxide nanoparticles in a single step. This approach not only suppresses particle aggregation but also preserves the molecular integrity of surface modifiers under high-temperature reaction conditions. Taking the preparation of gadolinium oxide as an example. Through modifier molecules on Gd₂O₃ surfaces, the hydrophilicity is markedly enhanced, enabling stable dispersion in aqueous media, which is a critical prerequisite for biomedical applications. This green synthesis method, regulated by hydrogen-bonding interactions, overcomes safety concerns associated with organic solvents in traditional solvothermal techniques and gadolinium ion leakage in co-precipitation methods, while eliminating complex post-modification steps. The longitudinal relaxation rate (r1) of Gd₂O₃UPs-220, prepared by this method, achieves 8.43 mm^-1s^-1 at a magnetic field strength of 7.0 T, demonstrating excellent magnetic resonance imaging (MRI) enhancement performance. This synthetic strategy provides an approach for preparing water-dispersible metal oxides.