Single gene differentiation by DNA-modified carbon electrodes using an AC impedimetric approach.

A simple and novel electrochemical biosensor is described for differentiating between differing gene sequences on the basis of DNA hybridization events. Polyethylenimine-modified screen-printed carbon electrodes were used to immobilize single-stranded PCR fragments from plasmid DNA from the gene for pyruvate kinase. AC impedimetric measurements were first performed on these systems in buffer and then upon exposure to single-stranded DNA. When the electrode and solution DNA were complementary, a large drop in impedance was measured. Complementary DNA could be clearly detected at concentrations down to 1 fg/mL. Higher concentrations gave faster hybridization with saturation occurring at levels above 1 ng/mL. Responses were much lower upon exposure to noncomplementary DNA, even at higher concentrations, with the sensor showing a high degree of selectivity. This sensor format offers great promise for many DNA hybridization applications and lends itself to mass fabrication.