Nanostructure of supported phospholipid monolayers and bilayers by scanning probe microscopy

Near-field scanning optical and atomic force microscopy were used to image structural details of supported lipid monolayers and bilayers. Compressed DPPC monolayers exhibited dense web-like structures whereas DPPE monolayers were more uniform with elongated inclusion domains of fluorescent probes. When a second lipid monolayer was self-assembled on a supported monolayer [Kalb et al., Biochim. Biophys. Acta 1103 (1992) 307], the structure of the resulting supported bilayer strongly depended on the coupling monolayer. On coupling monolayers of DPPC, the bilayers exhibited domains with finger-like extensions. Much more uniform bilayers were obtained when the coupling layer was DPPE. Towards the goal of developing a biosensor for the detection of viruses in biological fluids, bilayers were constructed with 10 mol% of the ganglioside G_D1a in the outer monolayer. Specific binding of influenza viruses to G_D1a receptors was monitored by total internal reflection fluorescence and atomic force microscopy.