Immobilization of DNA on nanostructured gold and silver substrates via alkanethiolate linkers: The influence of linker length

Various single-stranded DNA (ssDNA) chains were attached to nanostructured gold and silver surfaces highly active in surface-enhanced Raman scattering (SERS) spectroscopy. The DNA was attached to the metal surface using alkanethiol linkers with 6 or 3 carbon atoms in the chain, and then the metal surface was sealed with HS-(CH₂)_n-OH alkanethiols having the same number of carbon atoms in the chain as one of the linkers. The immobilized ssDNA was then hybridized with complementary ssDNA, which induced significant changes in the conformation of the chains of chemisorbed ω-substituted alkanethiols. For the first time, it has been investigated how the length of the alkanethiol chain through which the capture ssDNA is attached to the metal surface affects the DNA hybridization-induced changes in the measured SERS spectra. We found that the differences between the SERS spectra of the DNA layers recorded before and after hybridization were much larger when thiols with 6 carbon atoms in the chain were used as linking and sealing compounds than when compounds with 3 carbon atoms in the chains were used. This means that, in SERS DNA sensors based on the rearrangement of linking layers, using C6 linkers should make it easier than C3 linkers to observe the rearrangement based on SERS measurements. The properties of the monolayers formed from the compounds used to seal the metal surfaces with immobilized DNA chains (6-mercaptohexanol and 3-mercaptopropanol) were also analyzed. It was found that monolayers on silver generally form faster, but are less stable, than those formed on gold.