Oxidants are very active compounds that can cause damage to biological systems under specific environmental conditions. One effective way to counterbalance these adverse effects is the use of anti-oxidants. At low concentrations, an antioxidant is defined as a compound that can delay, control, or prevent an oxidative process. Antioxidants exist in plants, soil, and minerals; therefore, nature is a rich source of natural antioxidants, such as tocopherols and polyphenols. In nature, antioxidants perform in tandem with their bio-environment, which may tune their activity and protect them from degradation. In vitro use of antioxidants, i.e., out of their biomatrix, may encounter several drawbacks, such as auto-oxidation and polymerization. Artificial nanoantioxidants can be developed via surface modification of a nanoparticle with an antioxidant that can be either natural or synthetic, directly mimicking a natural antioxidant system. In this direction, state-of-the-art nanotechnology has been extensively incorporated to overcome inherent drawbacks encountered in vitro use of antioxidants, i.e., out of their biomatrix, and facilitate the production and use of antioxidants on a larger scale. Biomimetic nanoengineering has been adopted to optimize bio-medical antioxidant systems to improve stability, control release, enhance targeted administration, and overcome toxicity and biocompatibility issues. Focusing on biotechnological sciences, this review highlights the importance of nanoengineering in developing effective antioxidant structures and comparing the effectiveness of different nanoengineering methods. Additionally, this study gathers and clarifies the different antioxidant mechanisms reported in the literature and provides a clear picture of the existing evaluation methods, which can provide vital insights into bio-medical applications.

Biocidal activity and radical scavenging capacity (RSC), two seemingly opposing concepts, can coexist in engineered nanoceria (CeO₂) materials. In the present study, a series of CeO_2–x (x = 0–0.75) nanoparticles have been engineered utilizing the anoxic-flame spray pyrolysis (A-FSP) technology. A-FSP allows for tuning of the physicochemical and structural properties of CeO_2–x arising from lattice defects (Ce³⁺ and V_os) while maintaining minimal carbon incorporation. Our study aimed to understand the complex relationships between the biocidal and antioxidant activities of CeO_2–x, concepts whose origin was not sufficiently detangled in the bibliography. The biocide profiles of CeO_2–x nanoparticles toward the marine bacterium Aliivibrio fischeri were studied in tandem with their reactive oxygen species (ROS) scavenging capacity. A key finding of the present study is that the A-FSP process allows selective engineering of cluster-type Ce³⁺ and V_o defects, while typical, nonanoxic nanoceria structures (code-named ox-CeO₂) present mainly monomeric Ce³⁺ defects. The type of Ce³⁺ defects directly impacts the ROS scavenging efficiency. In addition, structural modifications that occur from the presence of cluster-type Ce³⁺ defects, such as larger particle sizes, are directly associated with lower biocidal activity. Thus, the findings of this study indicate that biocidal and ROS antioxidant activities are not mutually exclusive properties.