The adjacent effect between Gd(III) and Cu(II) in layered double hydroxide nanoparticles synergistically enhances T1-weighted magnetic resonance imaging contrast.

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Magnetic resonance imaging (MRI) is one key technology in modern diagnostic medicine. However, the development of high-relaxivity contrast agents with favorable properties for imaging applications remains a challenging task. In this work, dual Gd(III) and Cu(II) doped-layered double hydroxide (GdCu-LDH) nanoparticles show significantly higher longitudinal relaxivity compared with sole-metal-based LDH (Gd-LDH and Cu-LDH) nanoparticles. This relaxation enhancement in GdCu-LDH is also much greater than the simple addition of the relaxivity rate of the two paramagnetic ions in Gd-LDH and Cu-LDH, presumably attributed to synergistic T1 shortening between adjacent Gd(III) and Cu(II) in the LDH host layers (adjacent effect). Moreover, our GdCu-LDH nanoparticles exhibit a pH-ultrasensitive property in MRI performance and show much clearer MR imaging for tumor tissues in mice than Gd-LDH and Cu-LDH at the equivalent doses. Thus, these novel Gd/Cu-co-doped LDH nanoparticles provide higher potential for accurate cancer diagnosis in clinic application. To the best of our knowledge, this is the first report that two paramagnetic metal ions in one nanoparticle synergistically improve the T1-MRI contrast.