AVS 51st International Symposium
    Biomaterial Interfaces Wednesday Sessions
       Session BI2-WeM

Paper BI2-WeM3
Characterization of Surface Order and Structure of Thiolated Single-stranded DNA Oligomers on Gold by XPS and NEXAFS

Wednesday, November 17, 2004, 9:00 am, Room 213C

Session: Oligo Nucleotide - Surface Interactions
Presenter: L.J. Gamble, University of Washington
Authors: L.J. Gamble, University of Washington
C.-Y. Lee, University of Washington
N.T. Samuel, University of Washington
H.E. Canavan, University of Washington
D.G. Castner, University of Washington
Correspondent: Click to Email
The hybridization efficiency of DNA microarrays and biosensors is determined in part by variables such as the density and orientation of the single stranded DNA oligomers used to build the devices. In this study, we have used x-ray photoelectron spectroscopy (XPS) and near-edge x-ray absorption fine structure spectroscopy (NEXAFS) to characterize the surface order and structure of thiol-terminated ssDNA on gold. While NEXAFS provides an investigation of the order and orientation of the DNA oligomers at a surface, XPS provides a quantitative measure of the amount of DNA at a surface. We find that when thiolated DNA oligonucleotides (T)@sub 16@, (A)@sub 16@, and (A)@sub 8@(C)@sub 8@ are adsorbed to gold surfaces, their surface orientations vary differently with increased adsorption time. Time dependent studies of thiolated (T)@sub 16@ and (A)@sub 16@ oligomers by NEXAFS showed opposite polarization dependence between the two sequences possibly due to differences in their interactions with the gold surface. XPS results also indicate variations in the phosphorus to gold ratios among the three thiolated DNA oligomers over time. Furthermore, we explain these contrasting observations by examining the interaction of unmodified DNA strands that are non-specifically adsorbed to gold. Although polyT does not interact with the gold surface, polyA binds to gold possibly through the amine groups of the bases.