Anchoring Ligand-Effect on Bright Contrast-Enhancing Property of Hollow Mn₃O₄ Nanoparticle in T₁‑Weighted Magnetic Resonance Imaging

Here, we describe and conceptualize the influence of surface engineering for hollow manganese oxide nanoparticles (HMONs)-based contrast agents for magnetic resonance imaging (MRI). A systematic study has been conducted for enhancing the relaxivities of HMONs by functionalizing their surface with various capping ligands having different anchoring groups (carboxylate, alcohol, thiol, and amine). Among all studied ligands, carboxylate-anchored ligands exhibit significant increase in magnetization value upon surface capping of HMON. Contrary to the previous hypotheses based on the surface-Mn²⁺ ions accessibility to water molecules, we proposed surface capping induced magnetization in HMON is responsible for the enhanced relaxivity (r₁) value. Further, in vivo imaging efficacy of oleate-capped HMON (OA-HMON) has been demonstrated in mouse brain. This study provides an insightful understanding of contrast enhancement and modulation by surface ligands on manganese oxide-based T₁-contrast agents.