Reactive oxygen species (ROS) include the super oxygen free radical, hydrogen peroxide and its downstream product (peroxide and hydroxide) etc. ROS is involved in cell growth, proliferation, differentiation of development, aging and apoptosis as well as many physiological and disease process. The DCFH-DA (2, 7-dichlorofuorescin diacetate) is the most commonly used and most sensitive intracellular reactive oxygen detection probe. DCFH-DA has no fluorescence, it is hydrolyzed into DCFH (dichlorofluorescin) by ester hydrolysis enzyme after entering cells. DCFH can be oxidized to strong green fluorescence material DCF (dichlorofluorescein) that cannot pass through cell membrane when ROS exists. The excitation wavelength and the maximum emission wavelength of DCF is 502nm and 530nm respectively. The fluorescence intensity is proportional to the level of reactive oxygen species in cells.