Self-assembled monolayers of thiol-end-labeled DNA at mercury electrodes.

We show for the first time that thiol-end-labeled oligodeoxynucleotides form self-assembled monolayer (SAM) at Hg electrodes. Changes in voltammetric signals due to cytosine and Hg-S bond reduction indicated changes in positioning of the HS-(TTC)(7) molecules at the electrode with increasing HS-(TTC)7 concentration from lying flat with respect to SAMs, forming upright-standing molecules. This SAM behaved as an insulator not allowing electron transfer between [Ru(NH3)6]3+ and the electrode. Different adsorption modes of thiolated and thiol-free DNAs were observed.