Maria Puerto Morales

Iron oxide-based magnetic nanoparticles (MNPs) play a major role as contrast agents for magnetic resonance imaging (MRI). The introduction of Zn 2 + and Mn 2 + ions within their crystal lattice alters the magnetic anisotropy and the spin dynamical properties of the systems, which in turn influence the nuclear relaxation mechanisms that drive contrast enhancement in MRI. This work explored two sets of doped-magnetite MNPs (chemical formula Zn x Mn y Fe 3 − x − y O 4 ) with core diameters of d ∼ 4 or 15 nm produced by the fast and reproducible microwave-assisted synthesis method, and using different solvents like water or polyols. The d ∼ 4 nm MNPs were doped with Zn 2 + , from x = 0 to 0.9; for Zn 2 + = 0.5 , Mn 2 + was introduced at y = 0.2 , 0.4 . The d ∼ 15 nm MNPs were doped with Zn 2 + from x = 0 to 0.4, with Mn 2 + added at y = 0.1 for Zn 2 + = 0.3 and at 0.3 for Zn 2 + = 0.4 . Both sets were dispersed in water with carboxymethyl-dextran or polyacrylic acid coatings to ensure their colloidal stability, even under high magnetic fields. We highlighted the influence of the size and of the Zn 2 + / Mn 2 + doping on the static and dynamical magnetic properties, also through the H 1 -NMR-dispersion profile analysis over a wide frequency range and the application of the superparamagnetic relaxation heuristic model. Larger particles exhibited higher nuclear relaxometric efficiency and anisotropy compared to the smaller ones, consistently outperforming the commercial contrast agents. On the other hand, the magnetic response and the nuclear relaxivities are enhanced by a Zn 2 + content of x = 0.1 ions for approximately 4 nm MNPs and of x = 0.4 for approximately 15 nm MNPs, while a slight enhancing effect was obtained by Mn 2 + introduction. It is thus shown how a proper size and doping combination provide an attractive way to modify the static and dynamical magnetic properties of MNPs by acting on different spin-spin correlation times dominating in specific frequency intervals, thus enabling the fine-tuning of image contrast properties suitable for magnetic resonance imaging.

Magnetic particle hyperthermia relies on the efficient conversion of magnetic field energy into heat, yet the microscopic mechanisms governing this process within individual particles remain poorly understood. Here, we combine AC magnetometry experiments with dynamic micromagnetic simulations to connect microstructural features, magnetization dynamics, and macroscopic heat dissipation. We resolve heat generation at the intraparticle level, uncovering heterogeneous nanoscale heat-generation bursts with nanometer and nanosecond resolution. At a given particle size, grain size acts as an experimentally tunable parameter, balancing anisotropy disorder and pinning strength, thereby controlling both the magnitude and spatiotemporal distribution of heat release. Experiments show that flux-closure-dominated nanoflower architectures composed by larger grains generate more heat than their smaller-grain counterparts, whose deeper intraparticle pinning landscape redistributes heat generation over extended time windows. Together, our results provide a mechanistic framework linking nanoparticle microstructure to magnetic heating and establish design principles for optimizing nanoflowers as magnetic hyperthermia transducers.

Inflammation plays a pivotal role in a plethora of pathological processes, including spinal cord injury (SCI). However, effective anti‐inflammatory therapies for complex central nervous system pathologies remain an unmet clinical need. Herein, we present polymer‐coated iron oxide nanoparticles (IONPs) as an unprecedented platform combining bioactive coatings, an IL‐4 payload, and superparamagnetic properties validated on relevant in vitro and in vivo models. We demonstrate significant neuroactive and anti‐inflammatory actions driven by IONPs‐IL4 in comparison to soluble IL‐4. Interestingly, both hyaluronic acid‐coated and chitosan‐coated IONPs functionalized with IL‐4 (C12/HA‐IL4 and C12/CHI‐IL4, respectively) preserve maturation features and enhance firing frequency in primary neurons, while decreasing pro‐inflammatory markers in macrophages. In microglia cells, they decrease TNF‐α and increase Arg‐1 and CD206. Importantly, non‐functionalized IONPs also display a beneficial impact on neurons and macrophages. These nanoparticles can be successfully embedded into 3D porous reduced graphene oxide (rGO) scaffolds, retaining effective anti‐inflammatory properties in vitro. When examined in a chronic rat SCI model, rGO carrying C12/HA‐IL4 adequately integrates into the lesion, reduces vimentin at the interfaces, and facilitates total body weight recovery. These promising data encourage further investigation into the therapeutic potential of these nanosystems for SCI, thus paving the way for advanced SCI nanotherapeutics.

Microplastic remediation strategies often overlook the management and valorization of the recovered waste, limiting their overall sustainability. Herein, we propose a closed-loop water remediation strategy in which polyethylene terephthalate microplastics (MicroPET) are not only removed from water but also converted into new magnetic nanomaterials for subsequent remediation cycles. MicroPET was initially harvested using magnetic iron oxide nanoflowers (NFs) and subsequently depolymerized by neutral hydrolysis, achieving an unscaled gravimetric PET mass conversion of 97%. Upon process scale-up and downstream purification, an isolated monomer yield of 28.7% was obtained for both purified terephthalic acid (TPA) and ethylene glycol (EG), as confirmed by ¹H-NMR, FTIR, Raman, and osmometric analyses. The recovered supernatant from the unscaled hydrolysis was directly reused as the reaction medium for the microwave-assisted synthesis of maghemite magnetic iron oxide nanoparticles (MIONPs), producing bimodal single-core nanoparticles composed of 5 ± 1 and 29 ± 6 nm crystallites. Despite the absence of the multicore nanoflower architecture and the associated reduction in magnetic performance, the synthesized nanoparticles still demonstrated a remarkable MicroPET harvesting capacity of 1000 mg g⁻¹ under optimized conditions (compared with 10,000 mg g⁻¹ achieved by the original NFs). Furthermore, both the pristine nanoparticles and the MicroPET-loaded hybrid materials efficiently catalyzed methylene blue degradation through a heterogeneous Fenton-like process, with alternating magnetic field activation increasing the decolorization efficiency by ≈20% compared with room-temperature conditions. These results demonstrate that PET-derived EG can be directly reintegrated into the synthesis of functional magnetic nanomaterials, establishing a circular strategy that combines pollutant removal, plastic waste valorization, and catalytic water remediation.

Developing synthetic routes that are both scalable and structurally controlled is critical for translating functional nanomaterials into real-world technologies. Here, we demonstrate the microwave-assisted polyol synthesis of iron oxide nanoflowers (NFs), reducing reaction times from 16 (autoclave) to only 120 min while maintaining >90% reproducibility. Crystallographic alignment of the primary cores is achieved through a carefully optimized heating profile: slow ramp (0.2 °C s^–1) to 220 °C with a 20 min dwell, followed by microwave thermal sintering at 250 °C for 60 min to further enhance mesocrystal order. Magnetic anisotropy is tuned in situ by both sintering and cobalt incorporation, yielding improved magnetic performance and enhanced catalytic activity. electron paramagnetic resonance spectroscopy confirms reactive oxygen species generation with hydroperoxyl radicals (^•OOH) as the dominant species, while synchrotron X-ray absorption spectroscopy reveals changes in electronic state and local order that, together with the presence of specific redox-active sites, collectively enhance catalytic activity. The most ordered samples (NF5, NF7) display the highest ROS yields and benchmark magnetic hyperthermia performance, with specific absorption rate values up to 710 W g_NPs^–1 (NF5) and 542 W g_NPs^–1 (NF7) at 200 kHz/24 kA m^–1. Microwave-synthesized nanoflowers thus emerge as sustainable, reproducible, and multifunctional platforms coupling ROS generation with efficient magnetic heating.

Core@shell nanocatalysts that integrate magnetic and catalytic functionalities provide a versatile platform for remotely controlled reactions. Here, we report Zn_0.2Fe_2.8O₄ nanoparticles coated with a Cu­(II)-based shell, in which the zinc ferrite core generates heat under alternating magnetic fields, i.e., magnetic hyperthermia, while the copper shell exhibits heterogeneous Fenton-like activity. The ∼20 nm core shows high saturation magnetization (76 (4) emu/g) and superparamagnetic behavior at room temperature. Surface coating with an amorphous Cu­(II)-based phase is confirmed by XPS, EDS mapping, and ICP analysis. While bare Zn-ferrite nanoparticles show negligible Fenton-like activity, the copper-coated nanoparticles catalyze ·OH radical generation, as demonstrated by EPR experiments. The catalytic activity of the core@shell system remains low at room temperature but is strongly enhanced in magnetic hyperthermia conditions. Dye degradation assays using 100 ppm methylene blue and 1 mg/mL catalyst under alternating magnetic fields reveal that the core@shell system achieves 99% dye degradation in 1 h, exceeding the performance obtained under conventional thermal heating at equivalent bulk temperature. This enhanced performance could be attributed to a localized heating mechanism, in which the magnetic core acts as an internal heat source under alternating magnetic fields, promoting the heterogeneous redox reaction at the shell phase. These results demonstrate that the core@shell nanocatalysts with negligible activity at room conditions can be remotely enhanced by an alternating magnetic field, providing a promising strategy for applications where controlled catalytic activity is required.

Copper nanoparticles offer a cost-effective and sustainable alternative to silver-based materials for conductive inks in printed and flexible electronics. However, their practical application is often hindered by the need for inert atmospheres and environmentally hazardous reducing agents, but most critically by their rapid postsynthesis oxidation. In this work, we report a green, scalable synthesis of oxidation-resistant metallic Cu nanoparticles via a microwave-assisted polyol method using sodium hypophosphite as a nontoxic reducing agent and lignin as a capping and stabilizing agent. Nanoparticle formation occurs during a final microwave irradiation step as short as 5 min, following a brief homogenization stage, resulting in moderately polydisperse particles with average diameters around 150 nm and without the need for an inert atmosphere. The lignin coating significantly enhances the stability of the particles, maintaining their metallic state for over 120 days in ethanol and 60 days in air. Structural and compositional analyses confirm the effectiveness of lignin in preventing surface oxidation, while electrical conductivity tests show promising values (up to 3.83 × 10⁶ S/m, corresponding to a resistivity of 26.1 μΩ·cm), outperforming commercial references. These results demonstrate the potential of lignin-stabilized copper nanoparticles as eco-friendly conductive fillers for next-generation green and flexible electronics.

Accurately determining the Specific Loss Power (SLP) remains a major challenge in magnetic hyperthermia and photothermal heating. The SLPCalculator is an open access, easy-to-use and reliable tool for the SLP determination.

Magnetic hyperthermia therapy (MHT) is a promising cancer treatment that has demonstrated efficacy in phase I and II clinical trials for glioblastoma and prostate cancer. MHT relies on heat generated by magnetic nanoparticles (MNPs) when exposed to alternating magnetic fields (AMFs). The heat output depends not only on the intrinsic properties of MNPs but also on extrinsic factors such as the extracellular and intracellular environments. Aggregation of MNPs under certain conditions can significantly reduce therapeutic efficiency. To overcome this limitation, we present a strategy to enhance MHT by modulating MNP‐cell interactions. We functionalized dimercaptosuccinic acid (DMSA)‐coated MNPs with the 92R antibody (DMSA–MNPs@92R), which selectively binds to the low‐internalization chemokine receptor CCR9, overexpressed in certain tumors. Exposure of CCR9 ⁺ MOLT‐4 cells to DMSA–MNPs@92R under AMFs resulted in enhanced tumor cell death. Our approach enables spatially controlled binding, maintaining MNPs in a less‐aggregated state and at an optimal distance from the cell membrane to maximize heat generation. Mechanistic analysis confirmed that cytotoxicity is driven by localized hyperthermia at the subcellular level rather than a macroscopic temperature increase. These findings underscore the potential of controlled MNPs‐cell interactions to improve in vitro MHT performance and open an interesting avenue for enhancing therapeutic efficacy.

Zero-valent iron (ZVI) nanocatalysts are promising materials for environmental remediation (e.g., wastewater treatment) via advanced oxidation processes (AOPs) due to their ability to generate reactive oxygen species (ROS). However, their high reactivity often leads to rapid surface oxidation and a limited stability. This study evaluates the effect of different surface coatings on the stability and ROS production of ZVI nanocatalysts. The coatings tested include organic molecules such as mannitol and polyvinylpyrrolidone (PVP), as well as combinations with thin layers of metal hydroxides (M­(OH)₂, where M = Ni or Mn). Hydroxyl radical (^•OH) generation was quantified using electron paramagnetic resonance (EPR) spectroscopy over a period of 0 to 7 days in acetate buffer (pH 5). Results show that incomplete PVP coverage leads to a 90% decrease in ROS production within 24 h, while full coverage preserves catalytic activity for at least 1 day. Among inorganic coatings, Mn­(OH)₂ maintained stable ROS generation for 7 days, whereas Ni­(OH)₂ showed significant degradation after 24 h. These findings highlight the importance of coating selection and surface passivation to enhance ZVI stability and extend its catalytic performance in AOP applications, providing design guidelines for nanocatalysts in Fenton-like processes for water purification and environmental remediation.