Figure 1.

(a)Clamp-switch E-DNA sensor is composed of a DNA probe modified at its 3′-end with a methylene blue redox tag and at its 5′-end with a thiohexyl moiety for attachment on a gold electrode. The probe is designed with a first recognition element, a 15-base polypyrimidine portion (green portion) that can recognize a complementary target sequence via Watson–Crick base pairing. The second recognition element, a polypyrimidine sequence (red portion) can then fold back to form a triplex structure through Hoogsteen base pairing.^4,13 This brings the redox label into close proximity with the electrode surface, increasing electron transfer efficiency and resulting in an increase in the observed current (b).