From A Single DNA Strand, A Tiny Motor

May 15, 2002

GAINESVILLE, Fla. — They are still many years away, but infinitesimal molecular motors that could radically improve manufacturing and medicine just took a step closer to reality.

A University of Florida chemistry professor has made a “nanomotor” from a single DNA molecule. The motor, so small that hundreds of thousands could fit on the head of a pin, curls up and extends like an inchworm, said Weihong Tan, the principal investigator and lead author of an article about the motor in the April edition of the journal Nano Letters.

While it is not the first such DNA motor, Tan said his nanomotor is the first to be built from a single molecule rather than several different DNA molecules. This makes it easier to use and edges such motors closer to real-life applications in the rapidly emerging field of bionanotechnology, Tan said.

“Compared to other DNA motors, our nanomotor is more practical,” Tan said.

The first use of DNA motors is already beginning to emerge in the form of biosensors, said Hiroaki Yokota, a nanomotor researcher at Osaka University in Japan. These are instruments that researchers use to detect a very specific piece of DNA that may be related to disease. Such sensors “enable us to detect only a few DNA molecules that contain specific sequences and thus possibly diagnose patients as having such specific sequences related to a cancer gene or not,” he said.

Down the road, it is anticipated that nanomotors will play an active role in clinical treatment. For example, these ultra-small devices could be injected along with drugs that kill cancer cells or tumors, Tan said. When the drugs reach the disease site, the nanomotors would make the drug molecules attach and stick to the cancer cell membrane, Tan said. Perhaps more importantly, the motors’ precision would give them the ability to prevent the drugs from attaching to noncancerous molecules or healthy parts of the body – eliminating the debilitating effects, for example, of chemotherapy drugs.

Some scientists believe that nanomotors could also be used in so-called “test-tube manufacturing.” This approach turns traditional manufacturing on its head. Where traditional manufacturing creates structures from existing materials or parts, test-tube manufacturing involves building structures from the smallest molecular or atomic components.

U.S. and British scientists announced in 2000 they had built a tweezer-like motor that used synthetic strands of DNA for its structure. The motor had four DNA pieces: two for the tweezer’s V-shape, one that prompted the tweezers to close, and another that prompted the V-shape to open, according to news articles. At least one other group later announced another nanomotor, also built from multiple DNA strands.

DNA, short for deoxyribonucleic acid, holds the genetic keys to most living beings. In cell division, its double-helix structure divides so that each new molecule is identical to its parent. As a result of division and recombination in nature, DNA molecules have the capacity to recognize and bond with each other. Researchers tap this property when synthesizing new DNA molecules for motors. Like all motors, nanomotors need power. DNA is useful because it gets its energy through chemistry as opposed to traditional sources such as electricity.

“DNA is useful because it can participate in biological activities (as a result of) its real nature,” Yokota said. “It is difficult to build biologically active molecules from first principles.”

Tan said the problem with the multiple-DNA strand motors already completed is they are very difficult to control because the pieces are so tiny – on the order of tens of nanometers, where one nanometer equals one billionth of a meter. Each DNA strand requires an energy source, which also reduces the motors’ efficiency. With just one DNA strand, the UF nanomotor is easier to control and more efficient, Tan said.

The one-molecule motors also are easier to visualize, according to Hiroaki. “We can detect dynamic conformational changes of single DNA molecules individually without (the) average procedure used for multimolecule methodology,” he said.

Tan and colleague Jianwei Li, a UF chemistry research associate, synthesized the single molecule motor. They confirmed that it worked by attaching a light-emitting organic molecule to one end and a light-quenching molecule to the other. When the motor extended, separating the quencher and emitter, the light went on. When it curled up, the light went out.

Tan said it is difficult to predict when nanomotors, whether built from single or multiple molecules, will reach the stage when they can be used along with a drug or clinical treatment. He said the next step in his research is to coax his nanomotor to move a tiny particle from one place to another, demonstrating that it can perform a potentially useful task.