Monolayer properties of monosialioganglioside in the mixed diacetylene lipid films on the air/water interface

By combining the cellular membrane receptor GM1 with diacetylenic lipids, blue monolayer films can be created that undergo a colorimetric transition to red upon exposure to cholera toxin. The monolayer behaviour of GM1 in diacetylenic films was studied using the Langmuir-Blodgett technique with the goal of building colorimetric biosensors. Macroscopic characteristics of the films were obtained through analysis of surface pressure-area isotherms of GM1 and derivatized diacetylenic lipids at the air/water interface. Film optical properties and colorimetric response were optimized through modification of the ratio of receptor GM1 to diacetylene lipids and detection of the target analyte cholera toxin. Isothermic compression studies show that the mixed monolayers exhibit favourable film compressibility and high transferability as compared to the monolayers consisting of pure GM1. The impact of ionic strength and sub-phase pH on molecular interactions of lipids and miscibility of the mixed films is discussed. Contrary to usual temperature dependence observed for saturated fatty lipids, GM1/diacetylenic monolayers display an inverse relationship between temperature and surface pressure. (C) 1997 Elsevier Science Ireland Ltd.