Abstract

Two different methods were used to modify surfaces for covalent attachment of single stranded DNA probe sequences. In the first protocol, n-type Si (100) surfaces were modified by reduction of 4-nitrobenzendiazonium through cyclic voltammetry. Contact mode AFM was employed to produce holes in the deposited layer to determine layer thickness. Layer thickness was found to increase with the number of cyclic potential scans in both aqueous and acetonitrile media. In acetonitrile the layer thickness, after a single cyclic scan, was determined to be approximately 15 nm whereas, after three cyclic scans, the layer thickness was found to be approximately 35 nm. Layer thicknesses were also measured by ellipsometry and are in good agreement with the AFM results. In the second protocol, screen-printed carbon electrodes were functionalized using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide, under an applied potential of +2.2 V in aqueous acidic media. Both functionalized silicon and carbon surfaces were used to immobilize single stranded DNA-C 6 NH 2 sequences. Probe oligonucleotides were then attached to these surfaces and their hybridization with complementary strands was confirmed by fluorescence measurements. Electrochemical impedance measurements were used to detect hybridization of immobilized DNA. A significant shift in the flat band potential confirmed the hybridization event