Logo of the Physikalisch-Technische Bundesanstalt

Electrical conductivity of PLL-coated DNA origami structures

23.12.2020

AC dielectrophoresis between nanoelectrodes was used to contact DNA origami structures electrically, and the electrical conductivity of these structures was then measured. Structures with a poly-L-lysine coating exhibited conductivity values up to 2 μS.

DNA origami structures were examined as regards their applicability as radiation-sensitive detector material. In this context, their electrical conductivity would reflect the amount of radiation detriment [1]. In its natural environment inside cells, DNA is immersed in an aqueous solution. Outside this natural environment, the regular helicoidal structure of DNA might be damaged by denaturation due to environmental influences such as microhydration. However, this regular structure is vital for the transport of electrical charge carriers [2]. Exposure to air can therefore already affect DNA’s conductivity before it is even exposed to radiation. The DNA origami structures used for this experiment were designed as a multilayer, dense setup (as shown in Figure 1) to counter the effect of microhydration. In such a setup, the individual double helices are much more stable than individual strands. Furthermore, the origami structures were coated with a protective layer of poly-L-lysine (PLL) [3]. This protective coating proved to counter denaturation in solutions of low ionic strength.

representations of DNA origami structure

Figure 1: Schematic representation of (a) a DNA origami structure consisting of a bundle of 30 helices; (b) an AFM image of several structures on a mica surface, and (c) a TEM image of an individual structure.

Conductivity measurements after establishing electrical contact by means of AC dielectrophoresis (DEP) show that DNA origami structures that have not been modified are not conductive. In the case of the PLL-modified structures, ohmic conductivity values of up to 2 µS were measured.

In many cases, the local destruction of the electrodes and of the substrate has been observed (see Figure 2). This can be explained by the occurrence of high electric currents resulting from the contact established between highly conductive structures. Experiments are thus to be pursued to investigate whether it is possible to successfully contact and measure DNA origami structures which exhibit even higher electrical conductivity.

nanoelectrode pairs

Figure 2: SEM and AFM images of nanoelectrode pairs. Figure (a) shows the SEM image with a pair of intact electrodes prior to the immobilization of the DNA origami structures. The AFM images show (b) an intact pair of electrodes with contacted DNA origami structures, and (c) a pair of electrodes which was locally destroyed after DEP preparation.

References

[01]    Heimbach, F., Arndt, A., Nettelbeck, H. et al. Measurement of changes in impedance of DNA nanowires due to radiation induced structural damage. Eur. Phys. J. D 71, 211 (2017)

[02]    Boon, E., Barton, J. Charge transport in DNA. Curr. Opin. Struc. Biol. 12, 3 (2002)

[03]    Ponnuswamy, N., Bastings, M., Nathwani, B. et al. Oligolysine-based coating protects DNA nanostructures from low-salt denaturation and nuclease degradation. Nat Commun 8, 15654 (2017)

Contact

Opens local program for sending emailW. Y. Baek, Fachbereich 6.3, Arbeitsgruppe 6.36