Surface morphology and payload synergistically caused an enhancement of the longitudinal relaxivity of a Mn3O4/PtOx nanocomposite for magnetic resonance tumor imaging

Abstract

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/PtO_x 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 PtO_x 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/PtO_x NCs and the payload of ultrafine PtO_x 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/PtO_x 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.