JC-9 is a mitochondrial dye that stains mitochondria in living cells in a membrane potential‑dependent manner. At low concentrations, JC‑9 exists as a monomer and emits green fluorescence similar to that of fluorescein. At higher concentrations, the dye forms J‑aggregates, which exhibit a broad excitation spectrum and an emission maximum at approximately 590 nm. These properties make JC‑9 a sensitive indicator of mitochondrial membrane potential. JC‑9 is especially useful in apoptosis studies, as in apoptotic cells the dye remains in the cytoplasm and fluoresces green.
