Antioxidants are either man-made or natural substances that neutralize free radicals and prevent or delay some types of cell damage caused by oxidative stress, even at low concentrations. They can be classified as endogenous (glutathione and uric acid) and exogenous. Exogenous antioxidants include natural antioxidants, synthetic antioxidants like butylated hydroxytoluene (BHT), BHT analogs, butylated hydroxy-anisole (BHA) and Gallic Acid (GA) esters, nanoscale inorganic materials, and the most controversial and most recently discovered nano-encapsulated antioxidant molecules. Several foods, including fruits and vegetables, possess antioxidant potential, like vitamins (A, C, E, B3), carotenoids (lutein, β-carotene), and polyphenols (3,6-dihydroxyflavone), which exhibit free radical-scavenging activity. They are considered potent therapeutic agents for several ailments. However, some natural antioxidants possess poor water solubility, storage instability, and limited bioavailability due to their poor absorption and their degradation upon delivery. Synthetic antioxidants can cause reductive stress, which limits their applications. To overcome these problems, inorganic nanoparticles have been thoroughly studied for their antioxidant properties, and recently, nano-antioxidants have shown the ability to ameliorate oxidative stress with higher sensitivity, cellular antioxidant activity, lowest cytotoxicity, and targeted delivery. Nano-antioxidants are nanoparticles that are capable of capturing chain-carrying radicals and decreasing the number of initiation processes to alleviate the rate of autoxidation. Despite having their own antioxidant potentials, nanomaterials can be used as passive delivery systems for smaller antioxidants. Various combinations, including covalent interaction or the encapsulation of antioxidants with a variety of nanomaterials such as inorganic nanomaterials, metal nanomaterials, natural polymer-based nanomaterials, liposomes, or protein-polysaccharide-based conjugated nanomaterials, have been developed and are under examination for diverse applications. Nanomaterials are optimal for medicine and drug delivery systems because of their smaller size and extensibility. However, a complete understanding of the mechanism of action, origin, and physical and chemical nature of nano-antioxidant composites is required to understand their biological and catalytic activity.

Keywords: antioxidants; nanoantioxidants; oxidative stress; free radicals.