3,3'-Diethyloxadicarbocyanine iodide (DiOC2(3)) is a lipophilic carbocyanine dye widely used as a fluorescent probe for monitoring plasma membrane potential and mitochondrial membrane potential in living cells. It exhibits green fluorescence when bound to membranes and is particularly valuable in fluorescence microscopy, flow cytometry, and high-content screening assays to study cellular physiology, ion channel activity, apoptosis, and mitochondrial function. The dye's partition into organelles depends on membrane potential, allowing dynamic visualization of cellular structures and processes. It is also employed for general cell labeling and tracing axonal pathways in neuronal studies.