DNA immobilization onto electrochemically functionalized Si(1 0 0) surfaces

N-type Si(1 0 0) surfaces were modified by reduction of 4-nitrobenzenediazonium through cyclic voltammetry. Contact mode AFM was employed to produce holes in the deposited layers and cross-sectional profiles were obtained to determine their thicknesses. Layer thickness was found to increase with the number of cyclic potential scans in both aqueous and non-aqueous media. In acetonitrile, the single scan thickness was determined to be approximately 15 nm, whereas for three scans the layer thickness was found to be approximately 35 nm. These thicknesses were also measured and confirmed by ellipsometry. Both thicknesses are indicative of multilayer formation on the silicon surface. Layers formed in acetonitrile were more uniform and of better quality (without holes), compared to those prepared in water. This type of functionalized surface, after further cyclic voltammetric reduction of the nitro groups and treatment with glutaraldehyde, was then used to immobilize single strand DNA-C6H12NH2 probe sequences for hybridization with complementary DNA sequences. Fluorescein-labeled probe and target oligonucleotide sequences were used to validate the immobilization of the probe layer and hybridization with the complementary sequence. No binding was observed when using a non-complementary sequence as probe.