Like CFDA SE, CellTrace™ Oregon Green® 488 (carboxy-DFFDA SE) should be a useful tool for following proliferating cells. This Oregon Green® 488 probe passively diffuses into cells, where it is colorless and nonfluorescent until its acetate groups are removed by intracellular esterases to yield a highly fluorescent, amine-reactive dye. Upon reaction with intracellular amines, the probe forms Oregon Green® 488 conjugates that are well-retained by cells. Unlike fluorescein conjugates, Oregon Green® 488 conjugates exhibit bright, photostable green fluorescence that is independent of pH at typical cellular pH values (pH-6-8).