Abstract

4-nitrobenzenediazonium modified silicon substrates were used in the detection of immobilized 20-mer homo-oligonucleotides through electrical impedance measurement. The silicon (100) and (111) substrates were functionalized with the diazonium through cyclic voltammetry and the nitro group was subsequently reduced to an amino group by cyclic voltammetry. The functionalized substrates were activated with glutaraldehyde and the oligo-20mer with an amino-linker was immobilized onto the surface. Electrical impedance shows a negative shift in the flat-band potential upon immobilization of the oligo probe layer following glutaraldehyde treatment. Upon hybridization with the complementary oligo-20mer sequence, a positive shift in the flat-band potential was observed. A comparison between the immobilized oligo(dT) 20 and that of the oligo(dA) 20 demonstrated that the use of the oligo(dT) 20 as a probe layer is better than that of the oligo(dA) 20 . The results also show that the Si(100) oriented substrates performed better than the Si(111) substrates under the same conditions. Qualitative verification of the various modification steps up to glutaraldehyde treatment has been performed by X-ray photoelectron spectroscopy (XPS) and through Fourier transform infrared spectroscopy (FT-IR). Shifts in the flat-band potentials are observed following the various modification steps and these results show that the immobilization of the oligo(dT) 20 probe layer on the Si(100) substrates using a diazonium moiety is rapid and reproducible.