Magnetic resonance imaging (MRI) is one of the most powerful non‐invasive imaging modalities used in clinics due to its great spatial resolution and excellent soft‐tissue contrast, though still less sensitive than other techniques such as the nuclear imaging modalities. This lack of sensitivity can be improved with the use of contrast agents based on nanomaterials. In recent years, researchers have focused on the development of magnetic nanoparticles, given their role as enhancers of the contrast signal based on the magnetic resonance. Manganese ferrite nanoparticles stand out, given their high magnetic susceptibility and magnetic soft nature. Herein, 10 nm MnFe₂O₄ nanoparticles, functionalized with the natural antioxidant vitamin E (VitE‐MFO) are encapsulated into simple, biodegradable and non‐toxic nanoemulsions (NEs), by a reproducible one‐step method obtaining stable 150 nm‐sized magnetic nanoemulsions (VitE‐MFO‐NEs). After encapsulation, the superparamagnetic properties of VitE‐MFO are maintained and MR imaging studies reveal an extremely high transverse relaxivity for VitE‐MFO‐NEs (652.9 × 10⁻³ m⁻¹ s⁻¹), twofold higher than VitE‐MFO value. Moreover, VitE‐MFO‐NEs show great in vivo biocompatibility and good signal in in vivo and ex vivo MRI, which indicates their great potential for biomedical imaging enhancing the negative MR contrast and significantly improving the sensitivity of MRI.

Cancer causes millions of deaths each year and thus urgently requires the development of new therapeutic strategies. Nanotechnology-based anticancer therapies are a promising approach, with several formulations already approved and in clinical use. The evaluation of these therapies requires efficient in vivo models to study their behavior and interaction with cancer cells, and to optimize their properties to ensure maximum efficacy and safety. In this way, zebrafish is an important candidate due to its high homology with the human genoma, its large offspring, and the ease in developing specific cancer models. The role of zebrafish as a model for anticancer therapy studies has been highly evidenced, allowing researchers not only to perform drug screenings but also to evaluate novel therapies such as immunotherapies and nanotherapies. Beyond that, zebrafish can be used as an “avatar” model for performing patient-derived xenografts for personalized medicine. These characteristics place zebrafish in an attractive position as a role model for evaluating novel therapies for cancer treatment, such as nanomedicine.