ViaFluor™ 405-SE Cell Proliferation Dye is a fluorescent tracer that diffuses passively into cells and covalently labels intracellular proteins, resulting in long term cell labeling. It is non-fluorescent but fluoresces bright blue once it is hydrolyzed by intracellular esterases. The dye then reacts with intracellular amines forming fluorescent conjugates that are retained in the cell. The excess unreacted dye diffuses passively back to the extracellular medium and can be washed away. Immediately after staining, a single, bright fluorescent population will be detected by flow cytometry. With each cell division, daughter cells inherit roughly half of the fluorescent label, allowing the number of cell divisions that occur after labeling to be detected by the appearance of successively dimmer fluorescent peaks on a flow cytometry histogram compared to cells analyzed immediately after staining. Stained cells can be fixed with formaldehyde or gluteraldehyde based fixatives. ViaFluor 405-SE Cell Proliferation Dye is excitable by the 405 nm violet laser with a fluorescence emission maximum emits at 452 nm. The dye can be analyzed in the violet channel by flow cytometry, freeing other channels for multi-color fluorescence assays. Each kit contains 10 lyophilized dye vials, anhydrous DMSO for preparing stock solutions, and a labeling protocol. One kit can be used to label at least 2×108 cells; the final number of assays that can be performed per kit depends on the dye concentration used (see product protocol under downloads). Biotium also offers green fluorescent ViaFluor™CFSE and red fluorescent ViaFluor™568-SE Cell Proliferation Kits.