5′-Thiol oligonucleotides are normally used in covalent attachment to a gold particle or film and in immobilization through p-maleimidophenyl isocyanate to a solid surface (Nicewarner Peña et al., JACS, 2002, 25, 7314, Peterson et al., Nucleic Acids Res., 2001, 24, 5163, Adessi et al., Nucleic Acids Res., 2000, 20, e87). The length of the tether holding the thiol moiety can be varied to space the oligonucleotide away from the surface to overcome steric interference.