Characterization and Controlled Properties of DNA Immobilized on Gold Surfaces

We investigated the immobilization of single-stranded DNA (ssDNA) on gold using two complementary surface spectroscopies: Fourier transform infrared (FTIR) and x-ray photoelectron spectroscopy (XPS). Immobilization of ssDNA depends on its sequence and on the buffer composition. Buffers with higher salt concentration and divalent cations result in higher saturation densities of immobilized DNA. The relative adsorption affinities of homo-oligonucleotides for gold are strongly nucleobase-dependent: A > C >= G > T. The high affinity of oligo (dA) for gold causes dA . dT hybrids to denature and d (T-m-A(n)) block oligonucleotides to absorb on gold via the d (A) blocks. As a result, the d (T) blocks extend away from the surface in a brush-like conformation and the grafting density of d (T.-A,) is controlled by the length of the d (A) blocks. Applying this effect, a desirable brush-like conformation can be achieved at grafting densities < 10(13) DNA/cm(2) that are considered optimal for DNA hybridization.