The enzyme-like activity of metal oxide nanoparticles is governed by a number of factors, including their size, shape, surface chemistry and substrate affinity. For CeO₂ nanoparticles, one of the most prominent inorganic nanozymes that have diverse enzymatic activities, the size effect remains poorly understood. The low-temperature hydrothermal treatment of ceric ammonium nitrate aqueous solutions made it possible to obtain CeO₂ aqueous sols with different particle sizes (2.5, 2.8, 3.9 and 5.1 nm). The peroxidase-like activity of ceria nanoparticles was assessed using the chemiluminescent method in different biologically relevant buffer solutions with an identical pH value (phosphate buffer and Tris-HCl buffer, pH of 7.4). In the phosphate buffer, doubling CeO₂ nanoparticles’ size resulted in a two-fold increase in their peroxidase-like activity. The opposite effect was observed for the enzymatic activity of CeO₂ nanoparticles in the phosphate-free Tris-HCl buffer. The possible reasons for the differences in CeO₂ enzyme-like activity are discussed.

Microbial-induced calcite precipitation (MICP) is an innovative technology in civil engineering. However, the high cost of components and the fragility of the treated soil limit its wide use. One of the possible solutions is organic waste incorporation at different stages of the technology. In the present study, we consider the use of spent brewer’s yeast (BSY) to produce bacterial inoculates and wastepaper, flax shives and sawdust as reinforcing additives into the soil. We showed that the replacement of expensive components of LB medium by BSY extract increased biomass growth characteristics of Bacillus subtilis K51, B. cereus 4b and Micrococcus luteus 6 strains by 1.4, 1.5 and 1.8 times, respectively, while for B. subtilis 168, they were comparable to LB medium. The urease activities of all strains were not reduced compared to the control. Among the three kinds of cellulose-containing waste, wastepaper incorporation into MICP-treated soil samples led to an increase in compressive strength by 2.1 times and precipitated calcite percentage by almost 1.5 times compared to a sample without additives. Thus, we showed the potential for soil stabilization through MICP using organic waste.

A method is proposed for the preparation of stable sols of nanocrystalline cerium dioxide in nonpolar solvents, based on surface modification of CeO₂ nanoparticles obtained by thermal hydrolysis of concentrated aqueous solutions of ammonium cerium(IV) nitrate with residues of 2-ethylhexanoic and octanoic acids. The synthesis was carried out at temperatures below 100 °C and did not require the use of expensive and toxic reagents. An assessment of the radical-scavenging properties of the obtained sols using the superoxide anion-radical neutralization model revealed that they demonstrate notable antioxidant activity. The results obtained indicate the potential of the nanoscale cerium dioxide sols in nonpolar solvents to be used for creating nanobiomaterials possessing antioxidant properties.

Cerium dioxide sols stabilised with L-malic acid were shown to exhibit significant antioxidant activity towards alkyl peroxyl radicals in the range of ligand:CeO₂ molar ratios of 0.2–1 (0.2:1, 0.4:1, 0.5:1, 0.6:1, 0.8:1 and 1:1). The antioxidant activity of cerium dioxide nanoparticles greatly depended on L-malic acid content and increased by 8 times when the ligand:CeO₂ molar ratio increased from 0.2:1 to 0.4:1. An estimate of the ligand:CeO₂ molar ratio required to ensure complete surface coverage of CeO₂ nanoparticles with malate anions resulted in a value of 0.2. Aggregation degree of CeO₂ nanoparticles depends on the ligand:CeO₂ molar ratio. In the range of ligand:CeO₂ molar ratios 0.2–0.4, the size of aggregates decreased by an order of magnitude. The antioxidant capacity of 1 mM malate-stabilised cerium dioxide (0.2:1) relative to sodium ascorbate was 0.012 ± 0.001 mM. The antioxidant activity of cerium dioxide stabilised with L-malic acid at a ligand:CeO₂ molar ratio of 0.2:1 was 80 times less than the antioxidant activity of sodium ascorbate. Cerium dioxide nanoparticles stabilised with L-malic acid did not demonstrate a cytotoxic effect against human mesenchymal stem cells, in a wide range of concentrations (10⁻³–10⁻⁵ M), and their proliferation was stimulated after 72 h of cultivation. The results obtained show new possibilities for the design of biocompatible ceria-based nanomaterials with tunable pro- and antioxidant properties; these materials can further be assessed in view of their potential for treating oxidative stress-related disorders.

Background: The use of nanoradiosensitizers is a promising strategy for the precision enhancement of tumor tissue damage during radiotherapy. Methods: Here, we propose a novel biocompatible theranostic agent based on gadolinium fluoride doped with cerium and terbium (Gd_0.7Ce_0.2Tb_0.1F₃ NPs), which showed pronounced radiocatalytic activity when exposed to photon or proton beam irradiation, as well as remarkable MRI contrast ability. A scheme for the production of biocompatible colloidally stable Gd_0.7Ce_0.2Tb_0.1F₃ NPs was developed. Comprehensive physicochemical characterization of these NPs was carried out, including TEM, SEM, XRD, DLS, and EDX analyses, as well as UV–vis spectroscopy and MRI relaxation assays. Results: Cytotoxicity analysis of Gd_0.7Ce_0.2Tb_0.1F₃ NPs in vitro and in vivo revealed a high level of biocompatibility. It was shown that Gd_0.7Ce_0.2Tb_0.1F₃ NPs effectively accumulate in MCF-7 tumor cells. A study of their radiosensitizing activity demonstrated that the combined effect of Gd_0.7Ce_0.2Tb_0.1F₃ NPs and X-ray irradiation leads to a dose-dependent decrease in mitochondrial membrane potential, a sharp increase in the level of intracellular ROS, and the subsequent development of radiation-induced apoptosis. Conclusions: This outstanding radiosensitizing effect is explained by the radiocatalytic generation of reactive oxygen species by the nanoparticles, which goes beyond direct physical dose enhancement. It emphasizes the importance of evaluating the molecular mechanisms underlying the sensitizing effectiveness of potential nanoradiosensitizers before choosing conditions for their testing in in vivo models.