Sum-frequency generation spectroscopy of DNA monolayers

The anchoring of thiolated single-stranded DNA (HS-ssDNA) monolayers onto platinum substrates was investigated by sum-frequency generation spectroscopy. Different buffer solutions were used for the preparation of the adlayers. Vibrational fingerprints in the 2700-3100 cm(-1) spectral range showed the intercalation of Tris/EDTA (TE) buffer molecules within the HS-ssDNA self-assembled monolayer. Buffer contribution to SFG can be quenched either by using SFG inactive molecules like KH(2)PO(4)/K(2)HPO(4)/NaCl (PBS) or by repeated rinsing of the DNA layer with pure water. Comparing the SFG spectra of HS-ssDNA and mercaptohexanol (MCH), which had been self-assembled onto the same substrate, enabled us to infer ordering of the anchor arms and strong disordering of the DNA strands of HS-ssDNA monolayers self-assembled on platinum.