Ethidium homodimer 1, red fluorescent nucleic acid stain, 1 mg (3562-1mg)

Ethidium Homodimer 1 (EthD-1) is a high-affinity, red fluorescent nucleic acid dye impermeant to live cells and widely used to identify dead cells in biological research. EthD-1 is a dimeric analog of ethidium bromide, consisting of two ethidium moieties linked by a rigid bridge. Due to its large size and charged (dicationic) structure, EthD-1 cannot enter living cells with healthy membranes. In cells with compromised membrane integrity (dead or late-stage apoptotic cells), EthD-1 passively enters the cytoplasm and nucleus, where it intercalates into double-stranded nucleic acids (DNA and RNA) and exhibits a massive fluorescence enhancement (>40-fold) upon binding. The EthD-1 red emission is easily distinguishable from green fluorescent probes (e.g., GFP, FITC, Calcein, LUCS® 9, LUCS® 13), blue Hoechst stains, and far-red dyes (LDS 751, LUCS® 5), enabling easy multiplexing. EthD-1 is a standard dead-cell indicator in the viability and cytotoxicity assays, most commonly paired with green fluorescent live-cell stain like Calcein AM, LUCS® 9, or LUCS® 13. It is also used as a counterstain in fluorescence microscopy. Note that, while highly specific for dead cells in short-term assays, prolonged exposure can lead to its uptake by live cells, as it is mildly cytotoxic and can eventually permeabilize membranes.