Morphological studies of oligodeoxyribonucleotides probes covalently immobilized at polystyrene modified surfaces

The immobilization of short ss-DNA (18- and 36-mer) and their hybridization were studied at gold and glassy carbon substrates modified with low molecular weight (approximately 12, 18 and 24 kg/mol) polystyrene thin films. Amino-modified DNA was attached to the surface by reaction with succinimide ester groups bound to the polystyrenes. A ferrocene modified DNA target was used to confirm the probe-target hybridization. Atomic force microscopy studies showed significant morphological changes after probe immobilization and hybridization compared to the featureless structure of the polystyrene film. Single-stranded DNA samples had a globular morphology with an average density of 3.8 and 2.2 (x 10(11)) globules/cm2 for the 18- and 36-mer, respectively. The formation of a porous structure with a 2.0 and 1.0 (x10(11)) average pore density corresponding to the 18- and 36-mer was observed after hybridization. A surface composition analysis was done by X-ray photoelectron spectroscopy to confirm and support the images interpretation. Ferrocene oxidation (+323 mV/18-mer, +367 mV/36-mer, versus Ag/AgCl) proved the presence of ds-DNA at the modified surfaces.