AVS 53rd International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP31
Scanning Tunneling Microscopic Observation of Phospholipid Adlayer on Gold as a Model Cell Membrane

Tuesday, November 14, 2006, 6:00 pm, Room 3rd Floor Lobby

Session: Surface Science Poster Session
Presenter: T. Yamada, RIKEN, Japan
Authors: T. Yamada, RIKEN, Japan
S. Matsunaga, The University of Tokyo, Japan
R. Yokomori, The University of Tokyo, Japan
D. Ino, RIKEN, Japan
M. Kawai, The University of Tokyo, Japan
Correspondent: Click to Email
Microscopic view of cell membranes in the molecular scale has been desired concerning the domain structures, or "rafts", formed by various phospholipids, which are related to important biochemical functions caused by inclusion of proteins. Physical-chemistry-based model study is needed to estimate the interaction between lipid molecules and to obtain information about domains formed with different kinds of phospholipids. We attempted to obtain STM images of phospholipid adlayer spread on modified gold substrates. First a Au(111) substrate modified by octanethiol was immersed in a neutral ammonium perchlorate buffer solution (50 mM, pH7.0), and the thiol adlayer was examined by STM within the solution. The thiol-covered surface was characterized by pores with diameters less than 10 nm, of which bottoms were also covered with thiol. Individual molecules within the adlattice were also discerned. Then the buffer solution was added with 1,2-dihexanoyl-sn-glycero-3-phosphocholine below the critical micellar concentration at 0.0 V vs. RHE of the Au electrode potential. Sequential STM images of a fluidic lipid adlayer spreading along the surface were obtained. The thickness of adlayer was observed to be a few angstroms. The motion of lipid monolayer was detected as deformation of holes on the monolayer. By changing the electrode potential to -0.2 V vs. RHE, the adlayer was gradually altered into solidified patches of striped patterns with a periodicity of 4 nm. By returning the potential to 0.0 V vs. RHE, the fluidic monolayer was restored. This change is considered related to polymerization of phospholipids. More times of potential cycling induced fragmentation of the solid striped patches. It was recognized that the functions of phospholipids are addressable on the viewpoint of nanometer-scale chemistry. The applicability of STM to lipid adlayer is promising. Some cross-checking spectroscopic evidences will be also presented.