Reactive Oxygen Species (ROS) are chemically-reactive free radicals derived from molecular oxygen. Living cells constantly generate low levels of ROS and free radicals which work as both intra- and intercellular messengers. High levels of ROS, however, damages the biological components of the cells, including proteins, lipids, and DNA. Additionally, oxidative stress reactions can interfere with many essential biological processes such as phagocytosis (immunity and inflammation), cell respiration (mitochondria), metal metabolism, lipid synthesis, lysosomes, xenobiotic biotransformation of organic compounds and cellular signaling. Accumulation of ROS is also associated with aging, apoptosis or necrosis, and is implicated in pathological conditions such as vascular diseases, diabetes, renal ischemia, arteriosclerosis, pulmonary disorders, inflammatory diseases, and cancer.

ZellX^® Cellular ROS Assay Kit uses the H2DCFDA (2′,7′-Dichlorodihydrofluorescein diacetate), a fluorogenic dye to measure the activity of hydroxyl, peroxyl and other reactive oxygen species (ROS) in living cells. Firstly, H2DCFDA diffuses inside the cells and subsequently intracellular esterase cleaves the acetyl groups on H2DCFDA to yield the non-fluorescent compound H₂DCF, which is rapidly oxidized by ROS to the highly fluorescent 2’,7’-Dichlorodihydrofluorescein (DCF). The fluorescence intensity is proportional to the ROS levels within the cell cytosol.