USING SELF-ASSEMBLY TO CONTROL THE STRUCTURE OF DNA MONOLAYERS ON GOLD - A NEUTRON REFLECTIVITY STUDY

Neutron reflectivity was used to determine the concentration profiles of oligomeric DNA monolayers on gold in high salt concentrations (1 M NaCl). These monolayers are of interest as models for DNA probe system s used in diagnostic devices. go facilitate its attachment, the DNA wa s functionalized at the 5' end with a thiol group connected to the oli gonucleotide by a hexamethylene linker. Concentration profiles determi ned from neutron reflectivity indicate that adsorbed layers of single- stranded DNA (HS-ssDNA) on bare gold are compact, suggesting the prese nce of multiple contacts between each DNA strand and the surface. Afte r treatment with mercaptohexanol, a short alkanethiol with a terminal hydroxy group, the DNA ''stands up'' and extends farther into the solv ent phase. These changes are consistent with the DNA remaining attache d through its thiol end group while contacts between DNA backbones and the surface are prevented by the formation of a mercaptohexanol monol ayer. The end-tethered HS-ssDNA layer readily hybridized to its comple mentary sequence, resulting in DNA helices with a preferred orientatio n toward the substrate normal.