The current study evaluates the role of reactive oxygen species (ROS) in bioeffects of magnetite nanoparticles (MNPs), such as bare (Fe₃O₄), humic acids (Fe₃O₄-HA), and 3-aminopropyltriethoxysilane (Fe₃O₄-APTES) modified MNPs. Mössbauer spectroscopy was used to identify the local surrounding for Fe atom/ions and the depth of modification for MNPs. It was found that the Fe₃O₄-HA MNPs contain the smallest, whereas the Fe₃O₄-APTES MNPs contain the largest amount of Fe²⁺ ions. Bioluminescent cellular and enzymatic assays were applied to monitor the toxicity and anti-(pro-)oxidant activity of MNPs. The contents of ROS were determined by a chemiluminescence luminol assay evaluating the correlations with toxicity/anti-(pro-)oxidant coefficients. Toxic effects of modified MNPs were found at higher concentrations (>10⁻² g/L); they were related to ROS storage in bacterial suspensions. MNPs stimulated ROS production by the bacteria in a wide concentration range (10⁻¹⁵–1 g/L). Under the conditions of model oxidative stress and higher concentrations of MNPs (>10⁻⁴ g/L), the bacterial bioassay revealed prooxidant activity of all three MNP types, with corresponding decay of ROS content. Bioluminescence enzymatic assay did not show any sensitivity to MNPs, with negligible change in ROS content. The results clearly indicate that cell-membrane processes are responsible for the bioeffects and bacterial ROS generation, confirming the ferroptosis phenomenon based on iron-initiated cell-membrane lipid peroxidation.

The production of stable and homogeneous batches during nanoparticle fabrication is challenging. Surface charging, as a stability determinant, was estimated for 3-aminopropyltriethoxysilane (APTES) coated pre-formed magnetite nanoparticles (MNPs). An important consideration for preparing stable and homogenous MNPs colloidal systems is the dispersion stage of pre-formed samples, which makes it feasible to increase the MNP reactive binding sites, to enhance functionality. The results gave evidence that the samples that had undergone stirring had a higher loading capacity towards polyanions, in terms of filler content, compared to the sonicated ones. These later results were likely due to the harsh effects of sonication (extremely high temperature and pressure in the cavities formed at the interfaces), which induced the destruction of the MNPs.

This study presents an analysis of a set of iron oxides nanoparticles (NPs) (γ-Fe₂O₃, α-FeOOH, δ-FeOOH, 5Fe₂O₃·9H₂O, and Fe₃O₄) as potential candidates for ferroptosis therapy in terms of a phase state, magnetic characteristics, and the release of Fe^2+/Fe³⁺ as ROS mediators. Due to the values of saturation magnetization for Fe₃O₄ (31.6 emu/g) and γ-Fe₂O₃ (33.8 emu/g), as well as the surface area of these particles (130 and 123 m²/g), it is possible to consider them as promising magnetically controlled carriers that can function with various ligands. The evaluation of the release of Fe²⁺/Fe³⁺ ions as catalysts for the Fenton reaction showed that the concentration of the released ions increases within first 3 h after suspension and decreases within 24 h, which probably indicates desorption and adsorption of ions from/onto the surface of nanoparticles regardless their nature. The concentration of ions released by all nanoparticles, except α-FeOOH-Fe²⁺, reached 9.1 mg/L for Fe³⁺ to 1.7 mg/L for Fe²⁺, which makes them preferable for controlling the catalysis of the Fenton reaction. In contrast, a high concentration of iron ions to 90 mg/L for Fe³⁺ and 316 mg/L for Fe²⁺ released from compound α-FeOOH-Fe²⁺ allows us to utilize this oxide as an aid therapy agent. Results obtained on iron oxide nanoparticles will provide data for the most prospective candidates that are used in ferroptosis-inducing systems.

At present, the widespread use of iron oxide nanoparticles, including for commercial purposes, requires strict preservation of their phase composition during their application. The choice of nanoparticle modifier and modification conditions is decisive due to their high sensitivity to oxygen in the case of using real conditions (O₂, pH change, etc.). In this work, we studied the change in the phase composition of magnetite nanoparticles after modification with 3-aminopropyltriethoxysilane (APTES) and oxidation with nitric acid in order to estimate the protective potential of the silica shell. After modification by APTES and oxidation with nitric acid, the nonstoichiometric nature of the magnetite nanoparticles according to XRD data increased, which indicates an increase in transition forms compared to the initial sample (magnetite content decreased to 27% and 24%, respectively). In contrast, Mössbauer spectroscopy data detected a decrease in the nonstoichiometric index due to APTES modification conditions, but strong oxidation after exposure to nitric acid. It also showed that by analyzing the data of the diffraction analysis and Mössbauer spectroscopy for the same sample, one can obtain information not only about the ionic composition of “magnetite”, but also about the distribution of iron ions of different charges over the crystalline and amorphous parts of the preparation.

Bimetallic FeCo and FeNi nanoparticles attract much attention due to their promising magnetic properties and a wide range of practical applications as recording and storage media, catalytic systems in fuel cells, supercapacitors, lithium batteries, etc. In this paper, we propose an original approach to the preparation of FeCo- and FeNi/N-doped carbon nanocomposites by means of a coupled process of frontal polymerization and thermolysis of molecular co-crystallized acrylamide complexes. The phase composition, structure, and microstructure of the resulting nanocomposites are studied using XRD, IR spectroscopy, elemental and thermal analysis, and electron microscopy data. The main magnetic characteristics of the synthesized nanocomposites, including the field dependences and the ZFC-FC curves peculiarities, are studied. It is shown that the obtained FeCo/N-C nanocomposites exhibit exchange bias behavior at low temperatures. In turn, FeNi/N-C nanocomposites are ferromagnetically ordered.

FeCo and FeNi nanoalloy particles encapsulated in a nitrogen-doped carbonized shell (FeCo/C-N and FeNi/C-N) were synthesized by thermolysis at 400 °C of polyacrylamide complexes after frontal polymerization of co-crystallizate of Fe and Co or Ni nitrates and acrylamide. During the thermolysis of polyacrylamide complexes in a self-generated atmosphere, Co(II) or Ni(II) and Fe(III) cations are reduced to form FeCo and FeNi nanoalloy particles, while polyacrylamide simultaneously forms a nitrogen-doped carbon shell layer. This unique architecture provides high chemical and thermal stability of the resulting nanocomposites. The average crystallite size of FeCo and FeNi nanoparticles is 10 and 12 nm, respectively. The nanocomposites were studied by X-ray diffraction, atomic force microscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The nanocomposites have been tested as antifriction and antiwear additives in lubricating oils. The optimal concentrations of nanoparticles were determined, at which the antifriction and antiwear properties of the lubricant manifest themselves in the best possible way.