We report a facile synthesis of cube-shaped Co x Fe3–x O4 nanocrystals (NCs), which could be finely tuned in terms of NC size (from 15 to 27 nm) and cobalt stoichiometry (from 0.1 to 0.7). These particles exhibited high specific absorption rate (SAR) values, relevant for magnetic hyperthermia, and high relaxivity values, significant for magnetic resonance imaging applications. The peculiarity of these NCs is that already at low frequencies (such as 105 kHz, a working frequency used on human patients), they display SAR values that are three-times as large as those of iron oxide nanocubes of comparable sizes (and which were already considered outstanding). The highest SAR value recorded on the NCs reported here (915 ± 10 W/g(Co+Fe) at 105 kHz and 32 kAm–1) refers to particles with cubic shape, 20 ± 2 nm edge size, and Co stoichiometry between 0.6 and 0.7. The highest r 2 value (958 mM–1 s–1) was instead recorded on nanocubes with Co stoichiometry around 0.5/0.6 and size of 20 ± 2 nm. Remarkably, only at this specific size and Co stoichiometry were the NCs not perfect cubes but had a slightly concave shape, which together with their core–shell structure and magnetic parameters might account for the higher r 2 values recorded. NCs reported here, with optimized SAR and r 2 values, are promising tools for theranostic applications.

Nanoparticle‐based magnetic hyperthermia is a well‐known thermal therapy platform studied to treat solid tumors, but its use for monotherapy is limited due to incomplete tumor eradication at hyperthermia temperature (45 °C). It is often combined with chemotherapy for obtaining a more effective therapeutic outcome. Cubic‐shaped cobalt ferrite nanoparticles (Co–Fe NCs) serve as magnetic hyperthermia agents and as a cytotoxic agent due to the known cobalt ion toxicity, allowing the achievement of both heat and cytotoxic effects from a single platform. In addition to this advantage, Co–Fe NCs have the unique ability to form growing chains under an alternating magnetic field (AMF). This unique chain formation, along with the mild hyperthermia and intrinsic cobalt toxicity, leads to complete tumor regression and improved overall survival in an in vivo murine xenograft model, all under clinically approved AMF conditions. Numerical calculations identify magnetic anisotropy as the main Co–Fe NCs’ feature to generate such chain formations. This novel combination therapy can improve the effects of magnetic hyperthermia, inaugurating investigation of mechanical behaviors of nanoparticles under AMF, as a new avenue for cancer therapy.

The design of magnetic nanostructures whose magnetic heating efficiency remains unaffected at the tumor site is a fundamental requirement to further advance magnetic hyperthermia in clinic. This work demonstrates that the confinement of magnetic nanoparticles (NPs) into a submicrometric cavity is a key strategy to enable a certain degree of nanoparticle motion and minimize aggregation effects, consequently preserving the magnetic heat loss of iron oxide nanocubes (IONCs) under different conditions, including intracellular environments. We fabricated magnetic Layer-by-Layer (LbL) self-assembled polyelectrolyte submicrometric capsules using three different approaches, and we studied their heating efficiency as obtained in aqueous dispersions and once internalized by tumor cells. First, IONCs were added to the hollow cavities of LbL submicrocapsules, allowing the IONCs to move to a certain extent in the capsule cavities.Second, IONCs were co-encapsulated into solid calcium carbonate cores coated with LbL polymer shells.Third, IONCs were incorporated within the polymer layers of the LbL capsule walls. In aqueous solution, the higher specific absorption rate (SAR) values were related to the ones of free IONCs, while lower SAR values were recorded for capsule/core assemblies. However, after uptake by cancer cell lines (SKOV-3 cells), the SAR values of the free IONCs were significantly lower than those observed for capsule/core assemblies, especially after prolonged incubation periods (24 and 48 hours). These results show that IONCs packed into submicrocavities preserve the magnetic losses, as SAR values remained almost invariable. Conversely, free IONCs without the protective capsule shell agglomerated and their magnetic losses are strongly reduced. Indeed, IONC loaded capsules and free IONCs reside inside endosomal and lysosomal compartments after cellular uptake, show magnetic losses strongly reduced due to the immobilization and aggregation in centrosymmetrical structures in the intracellular vesicles. The confinement of IONCs into submicrometric cavities is a key strategy to provide a sustained and predictable heating dose inside biological matrices.

Lead-based halide perovskite nanocrystals are highly luminescent materials, but their sensitivity to humid environments and their biotoxicity are still important challenges to solve. Here, we develop a stepwise approach to encapsulate representative CsPbBr 3 nanocrystals into water-soluble polymer capsules. We show that our protocol can be extended to nanocrystals coated with different ligands, enabling an outstanding high photoluminescence quantum yield of ∼60% that is preserved over two years in capsules dispersed in water. We demonstrate that this on-bench strategy can be implemented on an automated platform with slight modifications, granting access to a faster and more reproducible fabrication process. Also, we reveal that the capsules can be exploited as photoluminescent probes for cell imaging at a dose as low as 0.3 μg Pb /mL that is well below the toxicity threshold for Pb and Cs ions. Our approach contributes to expanding significantly the fields of applications of these luminescent materials including biology and biomedicine.