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The assembly of DNA machines represents a central effort in DNA nanotechnology. We report on the first DNA rotor system composed of a two-ring catenane. The DNA rotor ring rotates in dictated directions along a wheel, and it occupies three distinct sites. Hg(2+)/cysteine or pH (H(+)/OH(-)) act as fuels or antifuels in positioning the rotor ring. Analysis of the kinetics reveals directional clockwise or anticlockwise population of the target-sites (>85%), and the rotor's direction is controlled by the shortest path on the wheel.

DNA nanotechnology is a rapidly developing research area in nanoscience. It includes the development of DNA machines, tailoring of DNA nanostructures, application of DNA nanostructures for computing, and more. Different DNA machines were reported in the past and DNA-guided assembly of nanoparticles represents an active research effort in DNA nanotechnology. Several DNA-dictated nanoparticle structures were reported, including a tetrahedron, a triangle or linear nanoengineered nanoparticle structures; however, the programmed, dynamic reversible switching of nanoparticle structures and, particularly, the dictated switchable functions emerging from the nanostructures, are missing elements in DNA nanotechnology. Here we introduce DNA catenane systems (interlocked DNA rings) as molecular DNA machines for the programmed, reversible and switchable arrangement of different-sized gold nanoparticles. We further demonstrate that the machine-powered gold nanoparticle structures reveal unique emerging switchable spectroscopic features, such as plasmonic coupling or surface-enhanced fluorescence.

A DNA construct consisting of a nucleic acid template, (1), on which a nucleic acid-modified glucose oxidase (GOx), (3), was hybridized by cooperative bridging of the T-Hg(2+)-T units, and a nucleic acid-functionalized ferrocene, (5), was directly hybridized on a Au electrode. The resulting nanostructure revealed bioelectrocatalytic activities, where the ferrocene units mediated electron transfer between the redox center of the enzyme and the electrode. The bioelectrocatalytic functions of the system are regulated by the concentration of Hg(2+) ions, which controls the content of the enzyme associated with the DNA template by means of the T-Hg(2+)-T bridging units. This phenomenon allowed the amperometric detection of Hg(2+) ions at a detection limit 1 x 10(-10) M with impressive selectivity.

A DNA tweezer consisting of C-rich arms is kept in the "closed" form by hybridization of the arms with a nucleic acid cross-linker. At acidic pH (pH = 5.2), the arms are stabilized through the formation of the i-motif, C-quadruplex structures, releasing the cross-linking nucleic acid and transforming the tweezer to its "opened" state. At neutral pH (pH = 7.2), the C-quadruplex structures are dissociated, resulting in the capturing of the cross-linking nucleic acid and the closure of the tweezer. By the reversible treatment of the tweezer at pH = 5.2 and at pH = 7.2, the tweezer system is cycled between the open and closed states, respectively, followed by a FRET process between a fluorophore-quencher pair that labels the tweezer. Also the concurrent activation of two DNA tweezers by pH stimuli is described. The pH-induced opening of one tweezer (tweezer A) by the formation of C-quadruplex (pH = 5.2) and the release of the cross-linking nucleic acid result in the closure of a second tweezer (tweezer B) by the hybridization of the released strand with the arms of tweezer B. The dissociation of the C-quadruplex structures (pH = 7.2) results in the favored translocation of the cross-linking nucleic acid from tweezer B to A. By the cycling of the pH of the system between pH = 5.2 and pH = 7.2, the concurrent opening and closure of the two tweezers are accomplished. The two tweezers system performs a SET-RESET logic gate operation, where the pH stimuli act as inputs.