Adsorption and surface dynamics of short DNA and LNA oligonucleotides on single-crystal Au(1 1 1) electrode surfaces

We have studied the surface dynamics of a double-strand decanucleotide (HS-10ATL) with 10 adenine-thymine base pairs linked to a Au(1 1 1)-electrode surface via a hexamethylene thiol linker. The study is based on a combination of voltammetry, interfacial capacitance data, electrochemical in situ scanning tunnelling microscopy, and X-ray photoelectron spectroscopy. The thymine bases of the oligonucleotide are connected to furanoses locked in a C3′-endo configuration called LNA (locked nucleic acid). Hybridization in solution is effected prior to linking to the Au(1 1 1)-surface. The melting point of the linker-free locked decanucleotide, 10ATL is >63 °C. However, voltammetric reductive desorption of the adsorbed thiol-modified double-strand decanucleotide, HS-10ATL, gives almost the same charge as single-strand HS-10A, 29 ± 3 and 27 ± 5 μC cm−2, respectively. In situ STM after HS-10ATL-immobilization also gives images showing highly ordered domains, virtually indistinguishable from those of immobilized HS-10A. X-ray photoelectron spectroscopy gives an N/P ration of 5.0 for HS-10ATL in line with the expected value for single-strand HS-10A (5.0).All three sets of data suggest that HS-10ATL hybridized in solution is significantly dissociated on binding to the Au(1 1 1)-electrode surface. This points to an adsorption mechanism in which a stable high density of Au-S bonds is achieved but at the expense of significant unzipping of the more voluminous duplex form.