Poloxamer 407 is a nonionic surfactant that is 100% active and relatively non-toxic to cells at low concentrations, and frequently used with dye AM esters such as Indo-1 AM, Fura-2 AM, Calcein AM, Fluo-3 AM, Fluo-4 AM, Quest Fluo-8? AM and Quest Rhod-4? AM, etc. to improve their water solubility.