Investigation of ordered ds-DNA monolayers on gold electrodes

Double-stranded DNA(poly(dA)(30).poly(dT)(30)) -modified gold electrodes, prepared by air-drying/adsorption method, have been investigated by various techniques, including cyclic voltammetry (CV), quartz crystal microbalance (QCM), electrochemical scanning tunneling microscopy (EC-STM), and surface-enhanced Raman scattering spectroscopy (SERS). CV and QCM results show that an average surface coverage of (7.5 +/- 0.2) x 10(-12) mol cm(-2) was obtained for poly(dA)(30).poly(dT)(30)-modified gold electrodes, close to the value for a saturated monolayer of ds-DNA lying flat on surfaces. EC-STM was used to evidence directly that ds-DNA forms a highly ordered and compact monolayer film on the gold substrate, whereas single-stranded DNA(poly(dT)(30)) adopts a coiled configuration and, therefore, cannot form an ordered structure on the gold substrate. Moreover, it was demonstrated, for the first time, by SERS experiments that partial denaturation of duplexes occurs arising from the different interfacial orientations of A and T bases on the gold electrode surface. The adsorptive nature of the surface-bound ds-DNA was also elucidated, which results in the obtained DNA-modified gold surfaces stable in a wide range of potentials.