Iron Bisphosphonate Metal-Organic Framework Nanoparticles as an Magnetic Resonance Imaging Probe for Spatial...

Accurate spatial detection of Helicobacter pylori (H. pylori) can potentially allow for the diagnosis and prevention of early stage gastric cancer. However, the hostile gastric environment and protective mucus layer surrounding H. pylori significantly hinder precise imaging. Here, an iron bisphosphonate metal organic framework nanoparticle (Fe-BP NPs) was synthesized for magnetic resonance imaging-based spatial detection of H. pylori. The Fe-BP NPs feature excellent stability under acidic conditions, a size of 120 nm, and a negatively charged surface, enabling rapid penetration through the mucus layer. It was discovered that in the NH₃-rich microenvironment generated by H. pylori, the Fe-BP NPs were sensitively and specifically transformed to ∼4 nm Fe(OH)₃ nanoparticles accompanied by an in situ switch of MR imaging mode from T₂-weighted to T₁-weighted. This transformation allows precise and vivid visualization of the H. pylori infection site. A further mechanistic study revealed that the NH₃-induced conversion of Fe-coordinated water molecules (Fe-H₂O) into Fe-OH^- species drives this transformation. When Fe-H₂O are exposed to NH₃, they readily form Fe-OH^- species, thus accounting for the decomposition of the Fe-BP to Fe(OH)₃. This work highlights the potential of MOFs to facilitate the highly sensitive and specific spatial detection of H. pylori, providing a robust tool for advancing disease diagnosis and monitoring.