Hyperpolarized Xe NMR signal advancement by metal-organic framework entrapment in aqueous solution

Significance Hyperpolarized 129Xe NMR/MRI is a useful method for diagnosis of diseases of the respiratory system. However, the sensitive detection of specific compounds in blood remains a challenge because of the weak 129Xe signal in aqueous solution. We developed a way, Hyper-SAME, to promote the 129Xe signal in aqueous solution. The 129Xe signal intensity is four times beyond that of free 129Xe in water and 200 times better than the benchmark molecular cage, cryptophane-A, in its saturated aqueous solution. Additionally, the hyperpolarized 129Xe signal can be amplified further by combining Hyper-SAME with hyperpolarized 129Xe chemical exchange saturation transfer. We report hyperpolarized Xe signal advancement by metal-organic framework (MOF) entrapment (Hyper-SAME) in aqueous solution. The 129Xe NMR signal is drastically promoted by entrapping the Xe into the pores of MOFs. The chemical shift of entrapped 129Xe is clearly distinguishable from that of free 129Xe in water, due to the surface and pore environment of MOFs. The influences from the crystal size of MOFs and their concentration in water are studied. A zinc imidazole MOF, zeolitic imidazole framework-8 (ZIF-8), with particle size of 110 nm at a concentration of 100 mg/mL, was used to give an NMR signal with intensity four times that of free 129Xe in water. Additionally, Hyper-SAME is compatible with hyperpolarized 129Xe chemical exchange saturation transfer. The 129Xe NMR signal can be amplified further by combining the two techniques. More importantly, Hyper-SAME provides a way to make detection of hyperpolarized 129Xe in aqueous solution convenient and broadens the application area of MOFs.