Short-lived fluorescence component of DPH reports on lipid--water interface of biological membranes.

Fluorescence measurements of 1,6-diphenyl-1,3,5-hexatriene (DPH) in large unilamellar phospholipid vesicles were performed to characterize the influence of the membrane physical properties on the short-lived lifetime component of the fluorescence decay. We have found that the short-lived component of DPH significantly shortens when the membrane undergoes a temperature-induced phase transition as it is known for the long-lived component of DPH. We induced membrane phase transitions also by alcohols, which are reported to be distributed different way in the membrane--ethanol close to the membrane-water interface and benzyl alcohol in the membrane core. A different effect of the respective alcohol on the short and long decay component was observed. Both the time-resolved fluorescence spectra of DPH taken during lipid vesicle staining and the lifetime dependences caused by changes of temperature and/or induced by the alcohols show that the short-lived fluorescence originates from the population of dye molecules distributed at the membrane-water interface.