Electrochemical Investigations of M-DNA Self-Assembled Monolayers on Gold Electrodes

Monolayers of double-stranded DNA on polycrystalline gold electrodes were prepared by chemisorbing SS-5‘-GTCACGATGGCCCAGTAGTT-3‘ (1) hybridized with its complementary strand 5‘-AACTACTGGGCCATCGTGAC-3‘ (2) onto gold through a disulfide linkage, giving a monolayer with hydroxylalkyl chains adjacent to the double-stranded DNA (ds-DNA). The system forms a stable and well-behaved ds-DNA monolayer on gold, which reduces the signal transduction between a solution electrophore and the gold surface. Upon addition of Zn2+ to the solution at pH 8.6, Zn2+ associates with the ds-DNA and form M-DNA. In contrast to ds-DNA, the signal transduction is significantly enhanced. The heterogeneous electron-transfer rate (k ET) between the ferricyanide electrophore and the surface was determined for bare gold, ds-DNA, and M-DNA monolayers. k ET for electron transfer from the solution electrophore to the gold surface through the M-DNA monolayer is 1.2 × 10-4 ± 0.2 × 10-4 cm s-1, which is smaller than for bare gold under the same conditions (k ET = 9.1 × 10-4 ± 0.2 × 10-4 cm s-1 ). For simple ds-DNA, k ET was too slow to be measured.