Imaging nanometer scale optical heterogeneities in phospholipid monolayers deposited on metal island films

Near-field scanning optical microscopy was applied to study the distribution of fluorescently labeled phospholipid monolayers deposited on the surface of gold island films by the Langmuir-Blodgett technique. Nanometer scale (approximately 50 nm) optical heterogeneities were observed in near-field fluorescence images of the monolayer deposited at 10 mN/m surface pressure. At higher surface pressure (30 mN/m) the heterogeneities became less pronounced. Overlaying of the near-field transmission and fluorescence images from the same area of the sample shows local transmission of gold island film is at a minimum where the fluorescence of the lipid monolayer is at a maximum. It was concluded that coverage of the metal island film by the Langmuir-Blodgett phospholipid monolayer is incomplete, and lipid molecules are preferentially localized in crevices of the film.