Phospholipid bilayers on a polyion-alkylthiol layer pair: microprobe imaging, electrochemical properties and peptide association

Atomic force microscopy (AFM) images of successive layers and peptide insertion in supported mobile phospholipid bilayers on polyion/alkylthiol layer pairs are reported. The morphology of each layer observed in a step-by-step adsorption process is correlated with electrochemical (cyclic voltammetry (CV)) and surface plasmon spectroscopy (SPR) results. The insulating properties of long-chain and short-chain alkylthiol layers are associated with a continuous layer and domain formation, respectively. The multilayer surface morphology is quantitatively characterized using roughness measurements for a large set of data involving root-mean-square roughness (RMS). Since the AFM observation with atomic and molecular resolution requires very flat and wide terraces to monitor the adsorption process, it is very important that initial surface morphology and roughness is known. Peptide association with the lipid membrane was studied by high resolution AFM in liquid, where pore formation was demonstrated for protegrin transmembrane insertion. The association of peptides with supported lipid bilayer of various compositions is discussed in terms of mobility and membrane permeability to charge transfer through the formation of pores.