Porous gold nanocluster-decorated manganese monoxide nanocomposites for microenvironment-activatable MR/photoacoustic/CT tumor imaging.

Stimuli-responsive nanoprobes that integrate multi-modal imaging capacities are highly desirable for precise tumor visualization. Herein, novel porous gold nanocluster-decorated manganese monoxide nanocomposites (MnO@Au NCs) were synthesized via a facile approach. The porous gold nanocluster layer was germinated on the surface of the as-prepared MnO@DMSA NPs through simple reduction of chloroauric acid in the presence of hydroxylamine hydrochloride. The MnO@Au NCs could be effectively internalized by tumor cells and slowly release Mn2+ ions within the acidic tumor microenvironment, improving the visualization of the tumor morphology. Benefitting from the porous architecture, the enhanced accessibility of Mn centers to proximal water molecules greatly augmented T1-weighted MRI contrast capacity. Compared with the conventional Mn-based contrast agents, the porous Au nanoclusters on MnO@Au NCs could delay the release of Mn2+ ions and thus effectively prolong the diagnostic time window. The broad near-infrared absorption of MnO@Au NCs features a high photoacoustic imaging depth than that of conventional gold nanospheres. Moreover, the Au nanoclusters exhibited desirable X-ray computed tomography contrast and rapid clearance from the living body. The as-prepared MnO@Au NCs hold great potential for accurate tumor imaging.