A twisting electronic nanoswitch made of DNA.

Single-stranded DNAs and RNAs that are rich in the nucleobase guanine form four-stranded G-quadruplexes, which are held together by hydrogen-bonded guanine quartets. In aqueous solution, both DNA duplexes and G-quadruplexes are modest conductors of electrical charge. A tight, topologically constrained DNA construct called twDNA is now reported, in which a core of four guanine-rich single strands structurally and electronically links together four DNA double helices. The addition and removal of K(+) or Sr(2+) cations promote alternative conformers of twDNA, which have strikingly distinct electronic properties. Unlike DNA mechano-electronic switches that require large conformational changes, twDNA requires only modest twisting/untwisting structural attenuations to achieve electronic switching.