Dipicrylamine (DPA) is a nonfluorescent anionic membrane dye. With its absorbance in the blue region of the visible spectrum, DPA can be used as a FRET quencher for a variety of fluorescent donor dyes. When applied to cells, DPA localizes at the interface of cytoplasmic membrane and aqueous phase in a manner sensitive to membrane potential change. A recent application of DPA is to measure cell membrane potential change by combining with the fluorescent donor dye DiOC16 (cat# 60038). The DiO/DPA system has been reported to produce a fluorescence signal change of >56% in HEK-293 cells and >25% in neuronal cultures and brain slices per 100 mV membrane potential change. Please also see the DiO/DPA membrane potential detection kit (cat# 30037).