Noncontact Atomic Force Microscopy - Yale School of Engineering ...

Comparative Studies on Water Structures on Hydrophilic and
Hydrophobic Surfaces by FM-AFM
Kazuhiro Suzuki 1 , Noriaki Oyabu 1,2 , Kei Kobayashi 3 , Kazumi Matsushige 1 ,
and Hirofumi Yamada 1 .
1 Department of Electronic Science and Engineering, Kyoto University, Kyoto, Japan
2 Japan Science and Technology Agency /Adv. Meas. and Analysis, Japan
3 Innovative Collaboration Center, Kyoto University, Kyoto, Japan
P.II-12
Water structures play essential roles in various biochemical functions such as selfassembly
of proteins and molecular recognition between ligands and receptors. Recently
we succeeded in three-dimensional molecular-scale visualization of water structures on
hydrophilic surfaces including a mica surface and a purple membranes using frequency
modulation atomic force microscopy (FM-AFM) [1].
In this study water structures on a hydrophobic highly oriented pyrolytic graphite
(HOPG) surface were investigated using FM-AFM. The results were compared with
those obtained on the hydrophilic mica surfaces. Figure 1 shows frequency shift-distance
curves measured on the HOPG surface (a) and on the mica surface (b). The oscillatory
behavior, originating from the water structure on each surface, can be observed in each
curve. However, there is a clear difference in the number of the water layers between the
two curves, which reflects the difference in the hydrophilicities of the two surfaces. In
addition, a possible effect of the hydration structure on the AFM tip surface was
investigated by using a chemically modified tip with a self-assembled monolayer film.
Figure 1: Frequency shift-distance curves measured on a hydrophobic HOPG surface (a) and on
a hydrophilic mica surface (b). Arrows indicate the peaks produced by the water layers.
[1] K. Kimura et al, The 11 th International Conference on Non-Contact Atomic Force Microscopy,
Madrid 2008, Oral Presentation Th-1200.
140