Electrochemical control of a DNA Holliday Junction nanoswitch by Mg2+ ions.

The molecular conformation of a synthetic branched, 4-way DNA Holliday junction (HJ) was electrochemically switched between the open and closed (stacked) conformers. Switching was achieved by electrochemically induced quantitative release of Mg2+ ions from the oxidised poly(N-methylpyrrole) film (PPy), which contained polyacrylate as an immobile counter anion and Mg2+ ions as charge compensating mobile cations. This increase in the Mg2+ concentration screened the electrostatic repulsion between the widely separated arms in the open HJ configuration, inducing switching to the closed conformation. Upon electrochemical reduction of PPy, entrapment of Mg2+ ions back into the PPy film induced the reverse HJ switching from the closed to open state. The conformational transition was monitored using fluorescence resonance energy transfer (FRET) between donor and acceptor dyes each located at the terminus of one of the arms. The demonstrated electrochemical control of the conformation of the used probe-target HJ complex, previously reported as a highly sequence specific nanodevice for detecting of unlabelled target [Buck, A.H., Campbell, C.J., Dickinson, P., Mountford, C.P., Stoquert, H.C., Terry, J.G., Evans, S.A.G., Keane, L., Su, T.J., Mount, A.R., Walton, A.J., Beattie, J.S., Crain, J., Ghazal, P., 2007. Anal. Chem., 79, 4724–4728], allows the development of electronically addressable DNA nanodevices and label-free gene detection assays.