We applied in-situ electrochemical scanning tunneling microscopy (in-situ EC-STM) to observe phospholipid layers over thiol-modified gold substrates as a model biological cell membrane. Our model cell membrane was 1,2-dihexanoyl-sn-glycero-3-phosphocholine, introduced on a monolayer of 1-octanethiol modified Au(111), in a neutral 0.05 M NH4ClO4 buffer solution. The lipid molecules formed a fluidic layer at the open-circuit potential. By cycling the electrode potential, the lipid layer reversibly changed over between the fluidic phase and a striped/grainy structure. This structural change might involve partial decomposition and oligomerization of phospholipids. This method will contribute for molecular biology by revealing the nanometer-scale structure of cell membrane.
