Current paper presents biological effects of magnetite nanoparticles (MNPs). Relations of MNP’ characteristics (zeta-potential and hydrodynamic diameters) with effects on bacteria and their enzymatic reactions were the main focus. Photobacterium phosphoreum and bacterial enzymatic reactions were chosen as bioassays. Three types of MNPs were under study: bare Fe₃O₄, Fe₃O₄ modified with 3-aminopropyltriethoxysilane (Fe₃O₄/APTES), and humic acids (Fe₃O₄/HA). Effects of the MNPs were studied at a low concentration range (< 2 mg/L) and attributed to availability and oxidative activity of Fe³⁺, high negative surface charge, and low hydrodynamic diameter of Fe₃O₄/HA, as well as higher Fe³⁺ content in suspensions of Fe₃O₄/HA. Low-concentration suspensions of bare Fe₃O₄ provided inhibitory effects in both bacterial and enzymatic bioassays, whereas the MNPs with modified surface (Fe₃O₄/APTES and Fe₃O₄/HA) did not affect the enzymatic activity. Under oxidative stress (i.e., in the solutions of model oxidizer, 1,4-benzoquinone), MNPs did not reveal antioxidant activity, moreover, Fe₃O₄/HA demonstrated additional inhibitory activity. The study contributes to the deeper understanding of a role of humic substances and silica in biogeochemical cycling of iron. Bioluminescence assays, cellular and enzymatic, can serve as convenient tools to evaluate bioavailability of Fe³⁺ in natural dispersions of iron-containing nanoparticles, e.g., magnetite, ferrihydrite, etc.

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.

Fullerene is a nanosized carbon structure with potential drug delivery applications. We studied the bioeffects of a water-soluble fullerene derivative, fullerenol, with 10-12 oxygen groups (F10-12); its structure was characterized by IR and XPS spectroscopy. A bioluminescent enzyme system was used to study toxic and antioxidant effects of F10-12 at the enzymatic level. Antioxidant characteristics of F10-12 were revealed in model solutions of organic and inorganic oxidizers. Low-concentration activation of bioluminescence was validated statistically in oxidizer solutions. Toxic and antioxidant characteristics of F10-12 were compared to those of homologous fullerenols with a higher number of oxygen groups:F24-28 and F40-42. No simple dependency was found between the toxic/antioxidant characteristics and the number of oxygen groups on the fullerene’s carbon cage. Lower toxicity and higher antioxidant activity of F24-28 were identified and presumptively attributed to its higher solubility. An active role of reactive oxygen species (ROS) in the bioeffects of F10-12 was demonstrated. Correlations between toxic/antioxidant characteristics of F10-12 and ROS content were evaluated. Toxic and antioxidant effects were related to the decrease in ROS content in the enzyme solutions. Our results reveal a complexity of ROS effects in the enzymatic assay system.

This study investigates the reactive oxygen species (ROS) generation and biological activity of novel silica-magnetite nanocomposites, TA-AA-Fe3O4 and TA-HA-Fe3O4, where TA is a silicon dioxide copolymer, AA is ascorbic acid, and HA is humic acids. A key challenge in nanotoxicology is the contradictory data from complex biological systems. To address this, we employed a standardized bioluminescent enzymatic assay (bacterial luciferase/oxidoreductase) as a simple, rapid biosensor system to evaluate the nanocomposites’ effects under controlled conditions. We compared ROS activity in both non-biological (enzyme-free aqueous solutions) and biological (enzymatic system) environments, with and without model oxidative stress induced by 1,4-benzoquinone. The enzymatic system exerted a pronounced neutralizing effect on ROS content, suppressing the significant ROS fluctuations and synergistic ROS generation (up to 300%) observed in non-biological media in the presence of the oxidizer. Additionally, the nanocomposites showed no effect on the bioluminescence intensity of the enzymatic system. This disparity between the higher reactivity in simple aqueous solutions and the neutral effect in the enzymatic system highlights the critical role of biological matrixes. The findings suggest that enzymatic environments can mitigate the radical processes driven by iron-based nanocomposites, which is crucial for predicting their biological activity and potential for applications like ferroptosis-based tumor therapy.