Manganese-Based Nanoscale Metal−Organic Frameworks for Magnetic Resonance Imaging

TLDR

Core–shell hybrid nanostructures offer an ideal platform for targeted delivery of imaging and therapeutic agents to diseased tissues. Manganese‑containing nanoscale metal–organic frameworks were synthesized by reverse‑phase microemulsion and microwave‑heated surfactant methods, characterized by SEM, TEM, TGA, PXRD, and ICP‑MS, and surface‑modified with a silica shell to covalently attach cyclic RGD peptide and fluorophore. The Mn‑NMOFs delivered large doses of Mn²⁺, achieving high in vitro and in vivo r₁ relaxivity and excellent MR contrast, while RGD functionalization enhanced cancer‑cell targeting for specific MR imaging in vitro and in vivo.

Abstract

Manganese-containing nanoscale metal−organic frameworks (NMOFs) with controllable morphologies were synthesized using reverse-phase microemulsion techniques at room temperature and a surfactant-assisted procedure at 120 °C with microwave heating. The nanoparticles were characterized using a variety of methods including SEM, TEM, TGA, PXRD, and ICP−MS. Although the nanoparticles gave a modest longitudinal relaxivity (r1) on a per Mn basis, they provided an efficient vehicle for the delivery of large doses of Mn2+ ions which exhibited very high in vitro and in vivo r1 values and afforded excellent MR contrast enhancement. The particle surface was also modified with a silica shell to allow covalent attachment of a cyclic RGD peptide and an organic fluorophore. The cell-targeting molecules on the Mn NMOFs enhanced their delivery to cancer cells to allow for target-specific MR imaging in vitro. The MR contrast enhancement was also demonstrated in vivo using a mouse model. Such core−shell hybrid nanostructures provide an ideal platform for targeted delivery of other imaging and therapeutic agents to diseased tissues.