CellTracker CM-DiI is a DiI derivative that is somewhat more water-soluble than DiI, thus facilitating the preparation of staining solutions for cell suspensions and fixed cells. CellTracker CM-DiI contains a thiol-reactive chloromethyl moiety that allows the dye to covalently bind to cellular thiols. Thus, unlike other membrane stains, the label is well retained in some cells throughout fixation and permeabilization steps. CellTracker CM-DiI is also available as 1 mg packaged into 20 vials, each containing 50 µg (C-7000).