|AVS 57th International Symposium & Exhibition|
|In Situ Microscopy and Spectroscopy Topical Conference||Wednesday Sessions|
|Session:||In Situ Microscopy/Spectroscopy – Biological Interfaces|
|Presenter:||T. Yamada, RIKEN, Japan|
|Authors:||T. Yamada, RIKEN, Japan
S. Matsunaga, The University of Tokyo, Japan
T. Kobayashi, RIKEN, Japan
M. Kawai, The University of Tokyo, Japan
|Correspondent:||Click to Email|
Scanning tunneling microscopy (STM) and other surface-scientific techniques can be utilized to explore the microscopic dynamics of biological molecules in the context that the techniques are applicable for solid surfaces immersed in aqueous solutions. We devised STM and vibrational spectroscopies to make usable for molecular monolayers at solid-liquid interface. We attempted to observe phospholipid layers formed on octanethiol-terminated gold (111) single-crystalline substrates placed in aqueous buffer solutions (in situ STM). By in situ STM we could observe dihexanoyl-sn-glycero-3-phosphocholine (DHPC), a relatively short kind of lipid, forming a fluidic monolayer. A crystalline phase of this monolayer was observed by applying an electrode potential compatible with the membrane potentials of real cells. Furthermore, mixed lipid layers have been examined by STM . We found some nanometer-scale raft structures (phase-separated domains), which are functionally characteristic for real cell membranes. We also studied phospholipid particles suspended in buffer solutions. Suspensions were prepared from a phosphcholine (PC) and an ethanolamine (PE), consisting of nanometer-scale phospholipid particles with narrow size distribution. In situ STM revealed particles with a diameter ~ 10 nm (named “minimal lipid particles (MLP)”), forming a monolayer along the Au(111). It is known that some categories of antibiotics selectively attack lipids contained in germ cell membranes and disintegrate the whole cells. We chose “duramycin”, a 19-residued peptide antibiotic, which specifically binds PE. When the total concentration of phospholipid was controlled between 100 μM and 500 μM, a layer of MLP was discerned. During STM scanning, 7 μM of duramycin solution was added into the suspension, and the PC+PE MLP became fragile and seemed to be scratched by the tip, ending up with a widespread multilayer. This sort of highly leveraged effect of duramycin is characteristic in the action of antibiotics . These works demonstrated the advantage of STM in monitoring the live nanometer-scale reactions of biological entities, which have not been recognized experimentally so far. We expect more application of STM in physiological investigation in cell biology.
 S. Matsunaga et al., Electrochem. Commn. 9 (2007) 645.
 S. Matsunaga et al., Langmuir 25 (2009) 8200.