Design and construction of an epifluorescence microscopic surface balance for the study of lipid monolayer phase transitions

Abstract

An instrumental design and construction details for the study of lipid monomolecular layers at the air-water interface using optical recording of fluorescent probes in the monolayer are discussed. The balance consists of a Teflon trough with a movable barrier mounted on a vibration-reducing platform. It is equipped with an epifluorescence microscopic attachment, and a Wilhelmy dipping plate connected to a force transducer that measures surface tension in the monolayer. Computer-controlled barrier movement can be utilized to give monolayer compression and expansion cycles at speeds up to 4 Å2/molecule/s. The epifluorescence microscope is coupled to a charge coupled device in tandem with a microchannel plate which permits observations at low light levels. This allows for use of small concentrations of probe molecules, thus reducing perturbation of monolayer properties by the probe. Images are recorded on videotape, digitized, and processed using operator-interactive software. Preliminary studies of phase behavior have been made for monolayers of dipalmitoyl phosphatidylcholine and a mixture of lipids.