Reactive oxygen species (ROS) are molecules containing hydroxyl radicals or peroxides with unpaired electrons. In healthy aerobic cells, ROS are produced naturally as a byproduct of oxidative phosphorylation, oxidoreductase enzymes, or metal catalyzed oxidation at a controlled rate. However, ROS can be induced under some stress conditions especially exposure to environmental oxidants and certain drugs that leads to oxidative stress. Exceed ROS can cause damages in the building blocks of cells including DNA, proteins, and lipids, and eventually results in cell death. Cell-permeant 2', 7'-dichlorodihydrofluorescein diacetate (H₂DCFDA) is a widely used ROS indicator. The reduced non-fluorescent fluorescein H₂DCFDA can be oxidized and converted into fluorescent 2’, 7’-dichlorofluorescein (DCF) by intracellular ROS. In this protocol, we applied H₂DCFDA to label the intracellular ROS and detected the DCF intensity by flow cytometry.

Mitochondrial membrane potential (Δψm) is an important parameter of mitochondrial function and an indicator of cell health. Depletion of Δψm suggests the loss of mitochondrial membrane integrity reflecting the initiation of the proapoptotic signal. Recently, lipophilic cationic fluorescent dyes have been developed to detect Δψm by accumulating in the mitochondrial matrix until the Nernstian equilibrium distribution of lipophilic cations is reached. In this protocol, we applied a cell-permeant, green-fluorescent, lipophilic dye 3,3'-dihexyloxacarbocyanine Iodide (DiOC6(3)) which accumulates in mitochondria due to their large negative membrane potential, it can be applied to monitor the mitochondrial membrane potential using flow cytometric detection.