Sequence-specific gene detection with a gold electrode modified with DNA probes and an electrochemically active dye.

A synthesized 20-mer DNA probe complementary to a part of an oncogene v-myc region having a mercaptohexyl group at the 5'-phosphate end was immobilized on a gold electrode by chemisorption. The immobilized DNA was detected voltammetrically using Hoechst 33258 with a DNA minor groove binder and an electrochemically active dye. The modified electrode was immersed into a 100 mumol/L Hoechst 33258 solution and washed with a phosphate buffer (pH 7.0). The anodic peak current (ipa) of Hoechst 33258 on the modified electrode was higher than that on a bare gold electrode (128 and 75 nA, respectively). It was considered that Hoechst 33258 was concentrated on the electrode surface due to its association with DNA. When the modified electrode was hybridized in a solution of a model targeted gene (10(-7) g/mL), single-stranded pVM623 containing the PstI fragment of a 1.5-kilobase pair of oncogene v-myc, the ipa was 192 nA. On the other hand, the ipa was 128 nA when the modified electrode was reacted in a solution of single-stranded pUC119 without a region complementary to v-myc in pVM623. The ipa was related to the concentration of the targeted DNA in the hybridization reaction. The use of Hoechst 33258 resulted in a sequence-specific detection of the targeted DNA quantitatively ranging from 10(-7) to 10(-13) g/mL in a buffer solution.