Next, the interaction between 0.5 ug/mL dsDNA was performed at the surface of SWCNT-PGEs in different interaction times. The TPT and guanine signals were evaluated by means of decrease %. The highest decrease % was obtained foe TPT and guanine signals after 15 min interaction time. After three repetitive measurements, the average signals of TPT and guanine were repectively measured as 2.2 +- 0.1 uA and 3.7 +- 0.2 uA after interaction of 0.5 ug/mL TPT and 50 ug/mL dsDNA for 15 min at the surface of SWCNT-PGEs. This result may be attributed that SWCNTs provided a large surface area, which caused by the requirement of longer duration for adsorption of DNA and drug molecules.