The average Rct value was found to be 36.5 +-21.8 ohm using unmodified PGEs . After CNT modification, there was 2-folds increase obtained at Rct due to the repulsive interaction between carboxylate SWCNT modified electrode surface and negatively charged ferricyanide ions. After immobilization of dsDNA, a6-fold increase was observed at the average Rct.