Dihydrorhodamine 123 is widely used as a fluorescent probe in biological research to detect reactive oxygen species (ROS) within cells. Its non-fluorescent form is oxidized by ROS, particularly hydrogen peroxide, to produce a highly fluorescent compound, making it a valuable tool for studying oxidative stress. This property allows researchers to monitor ROS generation in live cells, tissues, or organisms, providing insights into cellular health, disease mechanisms, and the effects of antioxidants. It is also employed in assays to evaluate the efficacy of drugs or compounds that modulate oxidative stress levels. Additionally, its application extends to flow cytometry and fluorescence microscopy for visualizing and quantifying ROS in real-time.