DNA nanotubes: the building blocks of life

Researchers at Caltech have succeeded in creating building blocks from DNA, which are able to connect to each other and create programmable structures, such as tubes of different diameters

High piles of articles and books have already been written about the vision of the nanotechnological machines. These machines will be a few nanometers in size - a billionth of a meter - and millions of them will be able to fit on the tip of a finger. But there is great difficulty in creating the machine components of these sizes, whether they are the rods, the bearings and all the other parts that make up a working machine. The difficulty comes from the fact that we cannot manipulate, even with the finest tweezers, the tiny molecules that make up the theoretical machines.

To overcome the problem, a solution was proposed that works in all living cells. The concept of 'self-assembly' describes a process in which molecules connect to each other by themselves, to create highly complex structures capable of acting in a variety of ways. The two most prominent advantages of this process are the reduction of the energy needed for the construction process, and the lack of need to physically intervene in the creation process. You only need to put the right components in the solution, and they will connect by themselves to create the right structures, according to the design. It can be thought of as Lego bricks that connect themselves to create the final structure. This phenomenon only occurs at the nanometric size, where the molecular building blocks are constantly 'trying' to connect to each other, and only the correct attachments remain at the end of the process.

Scientists at Caltech - the California Institute of Technology - have recently developed new nanometer-sized building blocks that are able to connect to each other and create nanotubes of different sizes. The new building blocks are made of one of the most common biological materials in the world: DNA.

DNA has always been considered an ideal building material for self-assembly. Two compatible DNA strands can recognize each other and stick together. Previous studies have already demonstrated that DNA can be used to create rigid building blocks known as 'tiles'. These tiles can connect to each other to create more complex structures, such as tubes. Although the process was successfully demonstrated, it was almost impossible to control the different diameters of the resulting tubes.

The new tiles created at Caltech consist of a single strand of DNA exactly 42 bases long, with four separate binding sites. The sites are able to link to each other in a certain orientation, similar to Lego blocks. With the help of proper planning of the tiles, it is possible to self-assemble tubes of different sizes. The diameter of the resulting tube is determined by the number of different tiles participating in its construction. For example, four tiles form a tube with a diameter of 12 billionths of a meter (12 nanometers). Five tiles form a tube with a diameter of 15 nanometers, and six tiles form a tube with a diameter of 18 nanometers.

"We are not the first to create DNA tubes with control over the diameter," says Peng Yin, a postdoctoral researcher at Caltech's Center for Advanced Biological Circuits and one of the authors of the study. "But compared to previous approaches, our method is explicitly simple and modular." The modularity of the method makes it possible to design tubes using a simple graphical abstraction system, which was also developed at Caltech in the last year.

Nanotubes of different diameters can be used to build a wide variety of nanostructures and for many uses. The mechanical properties of the tubes vary depending on the diameter. Thus, for example, thin tubes are also more flexible, and wide tubes are also stiffer. The nanotubes may also be used to create nanowires for electron conduction, and their diameter also has an effect on their conduction properties.

"The promise inherent in the simple approach of the single-stranded shingle is the creation of molecular systems that are more complicated than ever, using a method of self-assembly. This work is elegant and useful at the same time." says Eric Winfrey, associate professor of computer science, computational and neural systems, and bioengineering at Caltech. Most of the research was done in Winfrey's lab at Caltech.

The research was published in the prestigious scientific journal Science, under the name Programming DNA Tube Circumferences, and is considered another important step on the way to realizing the vision of nanotechnology and the creation of nanometric machines and structures.

For information on the Caltech website