Reflection anisotropy spectroscopy (RAS) has been used to show that at saturation coverage adenine adsorbs on the Au(110)/electrolyte interface in a base-stacking configuration with the plane of the bases orientated vertically on the surface and with the long axis of the molecules parallel to the [110] direction. Changes in the RAS observed from adsorbed adenine as a result of changes in the potential applied to the Au(110) electrode could arise from slight changes in the orientation of the molecules in the vertical plane.

It is demonstrated that the (1 × 1) structure and the (1 × 2) and (1 × 3) surface reconstructions that occur at Au(110)/electrolyte interfaces have unique optical fingerprints. The optical fingerprints are potential, pH and anion dependent and have potential for use in monitoring dynamic changes at this interface. We also observe a specific reflection anisotropy spectroscopy signature that may arise from anions adsorbed on the (1 × 1) structure of Au(110).

It is shown that the adsorption of cytosine at the Au(110)/liquid interface at a potential of 0.0 V "freezes" the Au(110) surface in the (1x1) structure and that the molecule does not change its orientation on the surface as the potential is varied. In contrast the adsorption of adenine does not freeze the Au(110) surface even though both molecules adopt a base stacking structure with individual molecules oriented in a plane vertical to the Au(110) surface with their long axes along [110] rows. It is suggested that cytosine bonds to three Au atoms through the NH(2) group, the N(3) and O(8) sites, and that this arrangement stabilizes the Au(110) surface and prevents its reconstruction to the more open (1x2) and (1x3) structures as the applied voltage is varied. The weaker bonding of the adenine molecule with the gold surface is unable to prevent the voltage induced reconstruction of the Au(110) surface.

It is demonstrated using Reflection anisotropy spectroscopy (RAS) that at sub-saturation coverage adenine adsorbs on the Au(110)/electrolyte interface in a base-stacking configuration with the plane of the bases orientated vertically on the surface and with the long axis of the molecules parallel to the [110] direction. This orientation is the same as that determined for saturation coverage. We also show that RAS can be used to determine the adenine coverage of the Au(110) surface.

Reflection Anisotropy Spectroscopy (RAS) is used to confirm that both single stranded (ss) and double stranded (ds) DNA formed ordered structures when adsorbed at Au(110)/phosphate buffer interface. The variation of the spectral intensity shows a cos 2θ dependence on the angle θ, which lies between the electric vector of the incident polarised light and the optical axes of the surface plane of the Au(110) establishing that the optical axes of both molecules are aligned with those of the Au(110) surface. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)