Tumor micro-environment sensitive 19F-magnetic resonance imaging in vivo

¹⁹F MRI has been paid great attention because of its higher signal-to-noise ratio and larger chemical shift than ¹H MRI. However, the low ¹⁹F content and sensitivity of environment limit its development in clinic. Herein, considering the large surface area and abundant metal active sites of metal organic framework (MOF) nanoparticles, we fabricated Zr-based MOF nanoparticles (UiO-66-F NPs) with an organic ligand of tetrafluoro-terephthalic acid (F₄PTA) as a pH-sensitive ¹⁹F MRI contrast agent, which remained stable in a neutral condition, but could release free F₄PTA in an acidic condition to enhance ¹⁹F MRI signal. As a proof of concept, UiO-66-F NPs-based contrast agent could turn on the ¹⁹F MRI signal in an acidic tumor micro-environment. The results provide an alternative strategy for the design of tumor micro-environment responsive ¹⁹F MRI contrast agents.