Engineers have created mobile nanofilms based on DNA

Sofia Dolotovskaya, N+1

Engineers from the University of Pennsylvania have created mobile nanofilms that work on the basis of specific hybridization of DNA molecules. You can control their movement by adding DNA chains to them, complementary to the DNA that is part of the film. The article was published in the journal Nature Nanotechnology (Shim et al., Shape changing thin films powered by DNA hybridization).

Here and below are drawings from the University of Pennsylvania press release
Penn Engineers and Chemists Make Nanoscale ‘Muscles' Powered by DNA – VM

The DNA molecule consists of two chains, each of which contains four types of nitrogenous bases: thymine, adenine, cytosine and guanine. Nitrogenous bases provide a connection between the chains, which is carried out according to the principle of complementarity: adenine connects only with thymine, and guanine – with cytosine. Such specific binding (specific hybridization) of DNA strands can be used to create mechanisms that change shape in response to the action of DNA molecules and set in motion various microscopic devices.

The authors of the article demonstrated the operation of this principle on the example of thin films created by them, which consist of gold nanoparticles connected to each other by bridges of single-stranded DNA molecules. These films consist of several layers, each of which is formed by DNA bridges with different sequences. When DNA complementary to any of these sequences is added to the solution containing the film, it changes shape: it bends, folds, or even turns over. This is due to the specific hybridization of DNA molecules embedded in the film with DNA molecules added to the solution. Double–stranded DNA is always longer than a single-stranded molecule with the same number of bases, because double-stranded DNA is more rigid, and single-stranded DNA is more flexible. And although when stretched, a single-stranded DNA molecule will be longer than a double-stranded one, in solution it gets tangled and becomes shorter. As a result, during the formation of double-stranded DNA, the bridge in the film lengthens, and the film material expands. It should be noted that this property of DNA can only be used to expand the film material, but not to compress it.

The movements of the film and its parts can be controlled by adding DNA molecules to it with different sequences complementary to different sections of the film. For example, if you add DNA molecules complementary to one layer of the film, the film will roll up into a "roll". The authors also provided a way to return such a rolled film to its original shape. To do this, they left DNA molecules, which, when added to the solution, lead to the folding of the film, "tails", non-complementary DNA bridges inside the film. When DNA molecules complementary to these "tails" are added to the folded film, new double-stranded molecules are formed that destroy old bonds. The DNA molecules complementary to the bridges break off, the bridge becomes short again, and the film returns to its original shape.

According to the authors, the uniqueness of such films lies in their high specificity. Unlike devices that respond to changes in temperature or acidity, films react only to certain DNA sequences that are complementary to their constituent bridges, and ignore all other DNA molecules. In the future, such films can be used, for example, in intracellular diagnostic devices that will report changes in gene expression.

The principle of DNA complementarity also underlies DNA origami, a technique that allows you to create nanoobjects from long DNA molecules with programmed properties: the shape and location of functional sections. This technique has been used, for example, to overcome drug resistance of blood cancer, to create molecular "wedges" capable of bringing together and removing molecules at a given distance with an accuracy of 0.4 angstroms, and to develop nanorobots that allow you to control the delivery of drugs with the power of thought.

Portal "Eternal youth" http://vechnayamolodost.ru  22.11.2016