Quantitative Surface Characterization of DNA Immobilized on Gold
D Y. Petrovykh, H Y. Kimura-Suda, L J. Whitman, Michael J. Tarlov
We describe the complementary use of x-ray photoelectron spectroscopy (XPS) and fourier transform infrared (FTIR) spectroscopy to quantitatively characterize the immobilization of thiolated poly(dT025 single-stranded DNA on gold. When electron attenuation effects are accurately accounted for in the XPS analysis, the relative coverage values obtained by the two methods are in excellent agreement, and the absolute coverage can be calculated based on the XPS data. The evolution of chemically-specific spectral signatures during immobilization indicates that at lower coverages much of the DNA lies flat on the surface, with a substantial fraction of thymine bases chemisorbed. At higher immobilized densities, the poly(dT)25 film consists of randomly-coiled ssDNA molecules each anchored via the thiol group and at possibly one or two other bases. We observe strong effects of different buffer salts on the immobilization efficiency and find surprising immobilization kinetics in a standard phosphate buffer. Buffers with divalent salts dramatically increase the efficiency of immobilization and result in very high surface densities (>5x10(sup 13)/cm(sup 2), densities that may only be possible if the divalent counterions induce strong attractive intermolecular interactions. In contrast with previous reports of alkanethiol adsorption kinetics on gold, ssDNA immobilization does not occur with Langmuir kinetics, a result attributable to reaarangement within the film that follows the initial adsorption.
alkanethiol, DNA, DNA microarrays, self-assembly
, Kimura-Suda, H.
, Whitman, L.
and Tarlov, M.
Quantitative Surface Characterization of DNA Immobilized on Gold, Langmuir
(Accessed December 7, 2023)