Description: 1,6-Diphenyl-1,3,5-hexatriene (DPH, excitation/emission=350 nm/420 nm) is almost non-fluorescent in water, but it exhibits a strong increase in fluorescence after intercalation into membranes and can be used as a probe for viscosity, polarity and lipid order. DPH has been used for the high-content imaging of neutral lipid droplets1 as well as a reporter of inner spore membrane fluidity in bacterial spores2.