i-Motif based pH induced electrochemical switches

Two C-rich DNA strands are employed to fabricate the intermolecular i-switch: strand 1 with thiol at the 5'-terminus immobilized on the gold electrode through the thiol-Au interaction, and ferrocene (Fc)-labeled strand 2 that hybridizes with strand 1 to form an i-switch nanostructure. In neutral or basic aqueous solution, the i-switch is present in the form of an extended duplex that makes Fc far away from the electrode; a weak faradaic current is obtained, so-called OFF state. While in the slight acidic condition, an obvious signal is detected from Fc which approaches the electrode due to the formation of the i-motif, so-called ON state. The faradaic current has a linear relationship with the pH value in the range of 5.8-8.0. (c) 2012 Elsevier B.V. All rights reserved.