Grafting of Gd-DTPA onto MOF-808 to enhance MRI performance for guiding photothermal therapy.

Gd(III) chelates are important T1-weighted contrast agents used in clinical magnetic resonance imaging (MRI), but their low longitudinal relaxivity (r1) results in limited imaging efficiency. In this study, we utilize a geometric confinement strategy to restrict a Gd chelate (Gd-DTPA) within the channels of a porous metal-organic framework material (MOF-808) for increasing its r1 relaxivity. Moreover, the Gd-DTPA-grafted MOF-808 nanoparticles were further surface modified with polyaniline (PANI) to construct an MRI-guided photothermal therapy platform. The resulting Gd-DTPA-MOF-808@PANI shows a high r1 relaxivity of 30.1 mM-1 s-1 (0.5 T), which is 5.4 times higher than that of the commercial contrast agent Magnevist. In vivo experiments revealed that Gd-DTPA-MOF-808@PANI has good T1-weighted contrast performance and can effectively guide photothermal ablation of tumors upon 808 nm laser irradiation. This work may shed some light on the design and preparation of high relaxation rate Gd-based contrast agents for theranostic application via utilization of versatile MOF materials.