Fe3O4–ZIF-8 assemblies as pH and glutathione responsive T2–T1 switching magnetic resonance imaging contrast agent for sensitive tumor imaging in vivo

A small Fe3O4 nanoparticles-based T1 contrast agent was assembled into a pH- and glutathione-responsive T2–T1 switching contrast agent, Fe3O4–ZIF-8. In vivo T1-weighted images of mice showed that Fe3O4–ZIF-8 displayed darkening contrast enhancement for liver sites, while darkening to brightening contrast enhancement at tumor sites, giving large inverse contrast for distinguishing the normal and tumor tissues.