Surface morphology and payload synergistically caused an enhancement of the longitudinal relaxivity of a Mn3O4/PtOx nanocomposite for magnetic resonance tumor imaging†
The construction of surface structures of manganese oxide nanoparticles (MONs) in order to promote their longitudinal relaxivity r1 to surpass those of commercially available Gd(III) complexes is still a significant challenge. Herein, we successfully obtained Mn3O4/PtOx nanocomposites (NCs) with an r1 of 20.48 mM−1 s−1, four times higher than that of commercially available Gd-DTPA (5.11 mM−1 s−1). The r2/r1 ratio of these NCs is 1.46 lower than that of Gd-DTPA (2.38). This is the first time that such excellent T1 contrast performance has been achieved using MONs via synergistically utilizing the surface morphology and surface payload. These NCs are composed of porous Mn3O4 “skeleton” nanostructures decorated with tiny PtOx nanoparticles (NPs) that are realized using laser ablation and irradiation in liquid and ion etching steps. Experimental results showed that the enlarged specific area of the porous Mn3O4/PtOx NCs and the payload of ultrafine PtOx NPs synergistically facilitated the T1 contrast capabilities. The former favors sufficient proton–electron interactions and the latter reduces the global molecular tumbling motion. These NCs also exhibit an evident computed tomography (CT) attenuation value of 24.13 HU L g−1, which is much better than that achieved using the commercial product iopromide (15.9 HU L g−1). The outstanding magnetic resonance (MR) imaging and CT imaging performances of the Mn3O4/PtOx NCs were proved through in vivo experiments. Histological examinations and blood circulation assays confirmed the good biosafety of the NCs. These novel findings showcase a brand-new strategy for fabricating excellent MON T1 contrast agents (CAs) on the basis of the surface structure and they pave the way for their practical clinical applications in dual-modal imaging.