DNA and DNA-based polymers are of interest in molecular electronics because of their versatile and programmable structures. However, transport measurements have produced a range of seemingly contradictory results due to differences in the measured molecules and experimental set-ups, and transporting significant current through individual DNA-based molecules remains a considerable challenge. Here, we report reproducible charge transport in guanine-quadruplex (G4) DNA molecules adsorbed on a mica substrate. Currents ranging from tens of picoamperes to more than 100 pA were measured in the G4-DNA over distances ranging from tens of nanometres to more than 100 nm. Our experimental results, combined with theoretical modelling, suggest that transport occurs via a thermally activated long-range hopping between multi-tetrad segments of DNA. These results could re-ignite interest in DNA-based wires and devices, and in the use of such systems in the development of programmable circuits.

properties of CNTs, the storage modulus and the dielectric constant of the composite were simultaneously improved by 20 and 30 %, respectively, in composites with 1 wt.-% CNTs. This improvement led to an enhanced strain response at reduced electric field and an increase in composite elastic energy density. It is remarkable that for the composites with even 0.5 wt.-% CNTs, a strain of nearly 2 % can be induced under a field of 54 V lm ±1 with an elastic energy density of 0.028 J cm ±3 in comparison with the neat terpolymer, where the strain at the same field level is 1.1 % and the elastic energy density is only 0.008 J cm ±3 . ExperimentalCNT/P(VDF-TrFE-CFE) composite films were prepared as described in the text. The terpolymer has a weight-average molecular weight, M w , of 670 000 g mol ±1 and a number-average molecular weight, M n , of 238 000 g mol ±1 , determined by gel-permeation chromatography using narrow-molecular-weight polystyrene standards and tetrahydrofuran as the mobile phase. The composite morphology was inspected by a Hitachi S-3500N scanning electron microscope with a secondary emission detector. The sample for scanning electron microscope was broken in liquid nitrogen, and the cross-section was examined. The SEM image was acquired with 5.0 kV acceleration voltage and at 20k magnification. XRD was performed in the stepscan diffraction mode using a Scintag Cu Ka diffractometer with an X-ray wavelength of 1.54 . T m and DH m were measured with a TA Q 100 instrument at a heating rate of 10 C min ±1 with sample weights around 5 mg. The mechanical properties were characterized by a TA DMA 2980 instrument in the step-scan mode at frequencies from 20 to 0.1 Hz. Samples for DMA were~100 lm thick.Gold electrodes were sputtered on both sides of the composite film for dielectric and strain characterization. Dielectric constant and loss were acquired using a HP multifrequency LCR (inductance, capacitance, resistance) meter (HP 4284A) while heating at a rate of 2 C min ±1. The longitudinal strain, in a direction parallel to the applied electric field, was measured by a piezobimorph-based photonic sensor [23]. [20] T m , DH m , and the storage modulus strongly depend on the composition, thermal history, and drawing ratio of the material. All samples in this study were annealed at 125 C for 5 hours without any further stretching. Higher T m , DH m , and storage modulus can be achieved for longer annealing times and with mechanical stretching.

G4-DNA, a quadruple helical motif of stacked guanine tetrads, is stiffer and more resistant to surface forces than double-stranded DNA (dsDNA), yet it enables self-assembly. Therefore, it is more likely to enable charge transport upon deposition on hard supports. We report clear evidence of polarizability of long G4-DNA molecules measured by electrostatic force microscopy, while coadsorbed dsDNA molecules on mica are electrically silent. This is another sign that G4-DNA is potentially better than dsDNA as a conducting molecular wire.

We describe a method for the preparation of novel long (hundreds of nanometers), uniform, inter-molecular G4-DNA molecules composed of four parallel G-strands. The only long continuous G4-DNA reported so far are intra-molecular structures made of a single G-strand. To enable a tetra-molecular assembly of the G-strands we developed a novel approach based on avidin–biotin biological recognition. The steps of the G4-DNA production include: (i) Enzymatic synthesis of long poly(dG)-poly(dC) molecules with biotinylated poly(dG)-strand; (ii) Formation of a complex between avidin-tetramer and four biotinylated poly(dG)-poly(dC) molecules; (iii) Separation of the poly(dC) strands from the poly(dG)-strands, which are connected to the avidin; (iv) Assembly of the four G-strands attached to the avidin into tetra-molecular G4-DNA. The average contour length of the formed structures, as measured by AFM, is equal to that of the initial poly(dG)-poly(dC) molecules, suggesting a tetra-molecular mechanism of the G-strands assembly. The height of tetra-molecular G4-nanostructures is larger than that of mono-molecular G4-DNA molecules having similar contour length. The CD spectra of the tetra- and mono-molecular G4-DNA are markedly different, suggesting different structural organization of these two types of molecules. The tetra-molecular G4-DNA nanostructures showed clear electrical polarizability. This suggests that they may be useful for molecular electronics.

The molecular morphology of long G4-DNA wires made by a novel synthetic method was, for the first time, characterized by high-resolution scanning tunneling microscopy (STM). The STM images reveal a periodic structure seen as repeating "bulbs" along the molecules. These bulbs reflect the helix morphology of the wires. The STM measurements were supported by a statistical morphology analysis of the DNA pitch length and apparent height relative to the surface. In the absence of X-ray and NMR data for these wires, the STM measurements provide a unique alternative to characterize the helix morphology.