Bioaffinity sensor using synthetic oligonucleotide-modified Au electrode

A 20-mer oligonucleotide whose 5'-end phosphate was modified with omega-thiohexyl group was applied in order to modify a Au electrode with its duplex form. Cyclic voltammograms of ferrocyanide/ferricyanide redox couple with the DNA-immobilized electrode gave the peak currents due to the reversible electrode reaction, which were significantly enhanced on adding acridine orange(AO). The cathodic peak current showed almost a Linear relationship with AO concentration in the range of 10(-7) - 7x10(-7) M, and then saturated beyond the concentration of 10(-6) M. From the concentration-dependent profiles, an apparent binding constant of (9.1 +/- 5.4) x 10(5) M-1 was obtained for the AO-DNA system. The obtained data agreed fairly well with the reported value (1.2 +/- 0.3)x10(6) M-1.