Content area
Full Text
Reactive oxygen species (ROS), resulting from the transfer of energy or electrons to oxygen, are highly reactive and potentially harmful to living organisms [1]. These ROS, such as singlet oxygen, superoxide, hydrogen peroxide, and hydroxyl radical, are essential intermediates in certain physiological processes (e.g., photosynthesis, respiration, and cell signaling), and their levels within cells are tightly controlled via enzymes (e.g., superoxide dismutase, glutathione peroxidase, and catalase) or antioxidants (e.g., ascorbic acid, cysteine, glutathione, bilirubin, carotenoids, and bilirubin). However, this redox homeostasis can be perturbed in many circumstances, and a burst of ROS, a condition termed oxidative stress, can induce deleterious effects to cells through oxidative damage of biomolecules (e.g., proteins, lipids, and nucleic acids) or disruption in cell signaling mechanisms [2].
Advances in nanotechnology, which deals with materials with dimensions of the order of 100 nm or less, have resulted in increasing commercial applications of engineered nanoparticles in consumer products, such as electronics, medicines, dietary supplements, food, clothing, cosmetics, and goods for children. The use of nanomaterials in diverse categories of consumer products suggests that broad populations of consumers will be increasingly exposed to nanomaterials [3,4]. A large number of studies have been conducted to evaluate the biological effects of nanoparticle exposure, and ROS-induced oxidative stress has been well recognized as one of the most important mechanisms when toxicity is observed [5].
Iron, which plays an active redox-catalytic role in many energy-transfer or electron-transfer processes due to its partially filled d orbitals and variable oxidation states, is inextricably linked to ROS chemistry. Engineered nanostructures of iron, including nano-iron metal and nano-iron oxides, have attracted commercial interest in areas of medicine (e.g., intravenous iron preparations, iron supplements, magnetic resonance imaging contrasting agents, drug and gene delivery, tissue engineering, and hyperthermia), food (e.g., iron fortificants), environment (e.g., remediation of soils and water by removal of organic pollutant and heavy metals), and agriculture (e.g., plant fertilizer and animal feed). Therefore, understanding ROS-related activities of nano-iron metal and nano-iron oxides could help address concerns over increasing incidences of biological exposure to these engineered nanostructures [6–11]. There are also widespread naturally-occurring iron nanostructures in diverse parts of terrestrial and aquatic ecosystems (e.g., soils, sediments, rivers, lakes, springs, and marine) mainly in the form...