Magnetic resonance imaging (MRI) has revolutionized medical imaging diagnostics with the advantages of non-invasive nature, absence of ionizing radiation, unrestricted penetration depth, high-resolution imaging of soft tissues, organs and blood vessels, and multi-parameter and multi-sequence imaging. Contrast agents (CAs) are crucial for enhancing image quality, detecting molecular-level changes, and providing comprehensive diagnostic information in contrast enhanced MRI. However, the performance of clinical Gd-based CAs represents a limitation to the improvement of MRI sensitivity, specificity, and versatility, thereby impeding the achievement of satisfactory imaging outcomes. In recent years, the development of magnetic nanoparticle-based CAs has emerged as a promising avenue to enhance the capabilities of MRI. Here, we review the advances in magnetic nanoparticle-based MRI CAs, including blood pool CAs, biochemically-targeted CAs, stimulus-responsive CAs, and ultra-high field MRI CAs, as well as the use of CAs for cell labeling and tracking. Additionally, we offer insights into the future prospects and challenges associated with the integration of these nanoparticles into clinical practice.

Molybdenum disulfide (MoS₂), a typical transition-metal dichalcogenide, has attracted increasing attention in the field of nanomedicine because of its preeminent properties. In this study, magnetic resonance imaging (MRI)-guided chemo-photothermal therapy of human breast cancer xenograft in nude mice was demonstrated using a novel core/shell structure of Fe₃O₄@MoS₂ nanocubes (IOMS NCs) via the integration of MoS₂ (MS) film onto iron oxide (IO) nanocubes through a facile hydrothermal method. After the necessary PEGylation modification of the NCs for long-circulation purposes, such PEGylated NCs were further capped by 2-deoxy-D-glucose (2-DG), a non-metabolizable glucose analogue to increase the accumulation of the as-prepared NCs at the tumor site, as 2-DG molecules could be particularly attractive to resource-hungry cancer cells. Such 2-DG-modified PEGylated NCs (IOMS-PEG-2DG NCs) acted as drug-carriers for doxorubicin (DOX), which could be easily loaded within the NCs. The obtained IOMS-PEG(DOX)-2DG NCs exhibited a T₂ relaxivity coefficient of 48.86 (mM)^-1·s^-1 and excellent photothermal performance. 24 h after intravenous injection of IOMS-PEG(DOX)-2DG NCs, the tumor site was clearly detected by enhanced T₂-weighted MRI signal. Upon exposure to an NIR 808-nm laser for 5 min at a low power density of 0.5 W·cm^-2, a marked temperature increase was noticed within the tumor site, and the tumor growth was efficiently inhibited by the chemo-photothermal effect. Therefore, our study highlights an excellent theranostic platform with great potential for targeted MRI-guided precise chemo-photothermal therapy of breast cancer.