Iron Bisphosphonate Metal–Organic Framework Nanoparticles as an Magnetic Resonance Imaging Probe for Spatial Detection of <i>Helicobacter pylori</i>

Accurate spatial detection of <i>Helicobacter pylori</i> (<i>H. pylori</i>) can potentially allow for the diagnosis and prevention of early stage gastric cancer. However, the hostile gastric environment and protective mucus layer surrounding <i>H. pylori</i> 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 <i>H. pylori</i>. 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 <i>H. pylori</i>, 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 <i>T</i>₂-weighted to <i>T</i>₁-weighted. This transformation allows precise and vivid visualization of the <i>H. pylori</i> 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 <i>H. pylori</i>, providing a robust tool for advancing disease diagnosis and monitoring.