DNA Nanotubes

Researchers at the Johns Hopkins Whiting School of Engineering have developed microscopic leak-free pipes using DNA strands. The diameter of each DNA pipe or nanotube is only about 7 x 10^-9 m and has a length almost similar to that of a dust particle. Despite being so small, the nano pipes have great potential as they could be used in the future to study complex diseases and deliver drugs directly to human body cells.

By combining different nanotubes together, scientists can develop large networks of DNA pipes and link those to different microscopic biostructures (structures found inside living organisms) to perform various tasks including the transfer of biomolecules. Such a network of nanotubes can act as tiny plumbings for various applications.

Explaining the potential of nanotubes further, one of the lead researchers and associate professor at Johns Hopkins University (JHU), Rebecca Schulman told IE, “Tinier plumbing might help us analyze individual molecules, which could help us make better drugs or enzymes, separate toxins, or even create better batteries by designing the conduits that ions flow through rather than using a porous material.”

She believes that although these technologies are still 10+ years away, their foundation is in things like nano-plumbing and being able to precisely measure and control the pipes the plumbing is made of.

The strange science behind nanotubes

Nanotubes are a highly evolved version of nanopores, small DNA structures proposed in some previously published studies. A nanopore is designed to serve as a conduit across a thin barrier between two chambers. Examples of such barriers are cell membranes (nanopores allow things to move in and out of a cell) and across metal or graphene sheets (like in nanopore-enabled DNA sequencing).

The key difference between nanotube and nanopore is length. The latter is typically 10-50 nm long and the type of leaking that occurs in it is of closed type (assuming it can be opened and closed), so a leaking nanopore doesn’t let anything through. On the other side, a nanotube has lengths in microns (in the range of 10^-6 m) and it functions like a real pipe capable of transporting material across barriers.

“In our case, we build a true pipe that can ferry material across a membrane and then another one micron or longer that can ferry material across a membrane barrier and then through a conduit to a final location a micron away,” said Professor Schulman. However, a different type of leak occurs in a microscopic pipe, similar to what you also see in plumbing -- holes in the walls of the tube that could let material leak out.

The researchers claim that their nanotubes are not leaky through the walls, and although they have nano-scale diameters, they don't get clogged. During the study, co-lead researchers Yi Li ran an interesting test to test the leak-free nature of the pipes. He filled a fluorescent liquid inside the tube, capped its ends, and then observed the change in the tube’s shape as the liquid moved inside.

No leaks occurred during the test. Moreover, since the tubes are made of DNA, the researchers reveal that they also have the ability to self-repair and self-assemble.

Limitations and the future of nanotubes

Professor Schulman suggests that a number of groups are currently pursuing nanotubes for use in drug delivery. They could be employed to direct the flow of molecules or ions between cells in engineered tissues. Such a type of application could be important for growing tissues in the lab like cardiac patches.

Although the applications of nanotubes seem promising, these are still limited to laboratory settings. So before bringing nanotubes to the mainstream, further research, animal studies, and clinical trials need to be performed.

When asked about the limitations of their study, professor Schulman told IE, one important caveat is that we only studied leaks for one type of molecule - a fluorescent dye. We will need to repeat these methods for other molecules to learn more about what types of molecules can easily be delivered or collected. We also expect that if we want to transport something smaller, like "ions" we will have to build a coating for the tubes, which we are also working on.”

The researchers are now planning to build large plumbing networks by connecting nanotubes as pipes and using nanopores as their fittings.

The study is published in the journal Science Advances.

Written by Rupendra Brahambhatt for Interesting Engineering

Photo by John Hopkins Whiting School of Engineering