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Scientists inch closer to building a drug-delivering nanorobot

Researchers say their proof-of-concept is a major step toward designing a nanocage that carries medicine around the body and targets specific diseased cells.

The nanocage consists of eight unique DNA molecules that respond to temperature changes to close (left) or open (middle) and ultimately trap (right) an active enzyme called horseradish peroxidase (HRP).
Sissel Juul

Scientists have been toying for years with creating tiny implants and nanorobots that could carry drugs to certain diseased cells. It is about as targeted as therapy can get, but at this point it's all a bit futuristic.

Within the confines of petri dishes, researchers are still tinkering. A new study is the first to demonstrate that a nanorobot, which the researchers are calling a DNA nanocage, can both encapsulate and release a biomolecule without degrading the cage itself -- and at a size small enough to keep the drugs trapped until they reach the end target.

The researchers used the body's own natural molecules to design eight unique DNA molecules that, when mixed together, form a nanocage. (See above illustration.)

By changing the temperature in the environment around the nanocage, the researchers were able to open the cage to allow a biomolecule to enter (at higher temperatures the DNA disassociates and is basically more porous) and then close it to trap it (at lower temperatures the DNA elements stick together). They chose to use the active enzyme horseradish peroxidase (HRP) because it is so easy to trace. The findings by researchers from Duke University in the US, Aarhus University in Denmark, and the University of Rome in Italy were published recently in the journal ACS Nano.

At just 15 to 20 nanometers across (1 nanometer being one-billionth of a meter), the tiny cage's cavity is small enough to house biomolecules such as HRP without releasing them prematurely -- which lead author Sissel Juul at Duke says has been the problem with other, larger 3D nanostructures.

"The beauty about working with DNA is that you can design it anyway you want," Juul said in an e-mail. "Say we wanted to encapsulate a smaller drug or bigger enzyme (compared to HRP), it would just be a matter of designing the DNA strands shorter or longer."

Juul added that adjusting the length of the DNA -- and thereby the amounts of hydrogen bonds -- can even allow for manipulating the temperature at which point the nanocage moves from a closed to an open state.

Thanks to this level of control, and the success the team has had in trapping and releasing HRP at very precise points, the researchers are confident that one day nanorobots will be used to transport medicine through the body to targeted cells -- carrying major implications for those battling cancer, diabetes, and so on.