Narrow Results

In order to develop a new DNA sequencing method by using chemical force microscopy (CFM), we have investigated the interaction of the hydrogen bonding between surfaces of nucleobase self-assembled monolayers (SAMs) and AFM-tips modified with the nucleobases. The two different adhesion forces, the jump-in force and pull-off force, between the AFM-tip modified with cytosine-SAM and the surfaces of four kinds of nucleobase SAMs were measured in water (20°C) by CFM. The adsorption of poly (C) onto a nucleobase-SAM on a gold electrode of quartz crystal microbalance (QCM) was measured as resonance frequency changes. The relative relation among four bases showed similar tendency in the adhesion force measured by the cytosine AFM-tip and in the adsorption amount of poly (C) on the QCM electrode as well as in the theoretically calculated interaction energies between two nucleobases.

The structural transformations of self-assembled dodecanethiol monolayers on the Au(111) surface have been studied using variable temperature scanning tunnelling microscopy (STM) in vacuum. Dark lines were observed to form at 350 K, followed by the completion of a rather regular zebra-stripe pattern at 360 K. The stripes have three distinct orientations, reflecting the three-fold symmetry of the substrate. There is continuous material transfer between the stripes at 360–390 K, leading to a constant change of shape of the individual stripes. The average width of the strips stays rather constant at ~ 5 nm. At 390 K, the zebra-stripe structure becomes unstable due to the desorption of thiol molecules.