Camouflage soft microrobots that undergo controlled shape and optical changes in response to a range of stimuli are of interest for microscale soft robotic and biomedical devices.The materials such microbots...

Iron oxide nanoparticles (IONPs) have been developed as contrast agents for T 1- or T 2-weighted magnetic resonance imaging (MRI) on account of their excellent physicochemical and biological properties. However, general strategies to improve longitudinal relaxivity (r 1) often decrease transverse relaxivity (r 2), thus synchronously strengthening the T 1 and T 2 enhancement effect of IONPs remains a challenge. Here, we report interface regulation and size tailoring of a group of FePt@Fe3O4 core–shell nanoparticles (NPs), which possess high r 1 and r 2 relaxivities. The increase of r 1 and r 2 is due to the enhancement of the saturation magnetization (M s), which is a result of the strengthened exchange coupling across the core–shell interface. In vivo subcutaneous tumor study and brain glioma imaging revealed that FePt@Fe3O4 NPs can serve as a favorable T 1–T 2 dual-modal contrast agent. We envision that the core–shell NPs, through interface engineering, have great potential in preclinical and clinical MRI applications.

How to resolve contradictions between the nanoscale size and high saturation magnetization (M s) remains one of the scientific challenges in nanoscale magnetism as the theoretical optimal M s of nanocrystals is compromised by the surface spin disorder. Here, we proposed a novel nanotechnology solution, heterointerface constructions of exchange-coupling core–shell nanocrystals, to rearrange the surface spin for the enhancement of M s of nanomagnetic materials. As a demonstration of this principle, single-interface coupling FePt@Fe3‑δO4 core/shell nanocrystals and multi-interface coupling FePt@Fe3‑δO4@MFe2O4 (M = Mn or Co) core/shell/shell nanocrystals were synthesized. The simulated and experimental results demonstrated that constructing coupling heterointerfaces orientates the overall magnetic moment, ultimately enhancing the M s of nanomagnetic materials. Moreover, this work first demonstrated that the origin of coupling heterointerfaces arose from mismatched lattices rather than chemical composition mismatch at the core–shell interfaces, thus providing both a solution to unite different mechanisms and an explanation to explain the exchange coupling at heterointerfaces.