Researchers turn photons into work using DNA

March 10, 2011 By Lisa Zyga feature
(Left) An illustration of the DNA-based molecular motor. The molecule is extended in its soft cis mode, and then contracted back to its original size in its stiffer trans mode, when work is extracted. (Right) An illustration of the DNA’s structure. Image credit: McCullagh, et al. ©2011 American Chemical Society.

( -- By using light to change the elasticity of a DNA molecule, scientists have designed a molecular motor that can turn light into mechanical work. Unlike most previously reported molecular motors, the proposed setup involves an atomic force microscope, which acts as an interface with the outside world and enables the work to be extracted.

The researchers, Martin McCullagh, Ignacio Franco, Mark A. Ratner, and George C. Schatz, from the Department of Chemistry and the Non-equilibrium Energy Research Center (NERC) at Northwestern University, have published their study in a recent issue of the .

The molecule that the scientists propose using as the central component of the motor is a DNA hairpin that includes two guanine-cytosine base pairs capped by an azobenzene compound. The scientists designed a of the system including the attachment of one end of the DNA hairpin to a surface and the other end to an coupled to a .

“The greatest significance of this work is showing how the structure of DNA can be exploited to amplify the transduction ability of azobenzene in a setup in which the work can be extracted,” Schatz told “To our knowledge, this is the first proposed DNA-based molecular motor with an interface to the outside world.”

In their molecular dynamics simulations, the researchers used light to change the structure of the azobenzene. In this process, called “isomerization,” the DNA-motor reversibly changes between the cis isomer and the trans isomer. Although this photoinduced isomerization is only a structural change, it has important implications, such as changing the length of the molecule (the trans isomer is longer) and altering the stability of the bonds between the guanine and cytosine bases (the trans isomer’s intra base pair interactions are stable across a greater range of lengths).

As the chemists showed, these two differences between the cis and trans isomers alter the molecule’s elasticity, and can be exploited to extract work from the system. For modest extensions, the trans isomer of the DNA hairpin is stiffer because it has a geometry that favors DNA base pairing, which makes it more difficult to extend the DNA hairpin.

To extract work from the system, the scientists proposed using a single-molecule analog of a thermodynamic cycle (a Stirling cycle). In this cycle, the molecule in its soft cis mode is first extended using the AFM setup. Next, light transforms the cis isomer into the stiffer trans isomer. The trans structure is then contracted to the motor’s original extension. Finally, a second light source is used to isomerize the molecule back to the cis state to close the cycle. Since the molecule is stiffer during contraction, the work extracted during contraction is larger than the work invested during extension, leading to net work extraction.

“The basis of this motor is the photoinduced change in elasticity of the azobenzene-DNA molecule,” Schatz said. “Because of the setup, the AFM is an integral part of the DNA motor. Work must be done on the molecule and cantilever to extend it, and work is extracted from the composite system during contraction. If the molecule is stiffer during contraction, then net work can be extracted.”

The scientists estimated a maximum of 3.4 kcal/mol of extractable work per cycle with an estimated maximum efficiency of 2.4%. This amount of work is comparable to the 7.3 kcal/mol of free energy output in ATP hydrolysis, which is the main energy source in biological processes.

“While the amount of extractable work from this motor is promising, the focus of this study is on investigating novel concepts in energy conversion,” Schatz said. “The proposed DNA-based motor provides a platform upon which further improvements can be made. We would like to highlight that the explored setup provides a means to quantify the transduction abilities of single molecules. Such quantification is a pivotal step in transforming single-molecule machines from scientific curiosity to actual power supplies for nanoscale processes.”

In the future, the scientists plan to use these insights regarding the relationship between a molecule’s structure and its function to improve the DNA-based motor design. They hope to find more optimal azobenzene-capped structures, as well as investigate the effect of temperature on the motor’s performance.

Explore further: Giving photochemistry a hand

More information: Martin McCullagh, et al. “DNA-Based Optomechanical Molecular Motor.” Journal of the American Chemical Society. DOI:10.1021/ja109071a


Related Stories

Giving photochemistry a hand

September 3, 2005

Making molecules with the right handedness - either a left- or a right-handed arrangement of atomic groupings - is of critical importance to the pharmaceutical industry, as the two different 'handed' forms (called enantiomers) ...

Single molecule motor inspired by natural energy conversion

January 23, 2006

A single molecule working as the nano scale version of the steam engine: that’s the molecular motor developed by a group of UT scientists led by prof. Julius Vancso of the MESA+ Institute for Nanotechnology. Natural ‘motor ...

Molecular motor structural changes imaged

September 14, 2006

A U.S.-led international team of researchers has shed new light on how tiny molecular motors that transport materials within cells generate energy.

Turning an axel mounted molecular wheel

January 23, 2007

Researchers at the Centre for Material Development and Structural Studies in Toulouse (CEMES-CNRS) and their colleagues at the Free University of Berlin have, for the first time, managed to control the rotation of a wheel ...

Researchers shake up scientific theory on motor protein

February 5, 2009

( -- An international team of scientists led by the University of Leeds has shed new light on the little-understood motor protein called dynein, thought to be involved in progressive neurological disorders such ...

A New Family of Molecules for Self-Assembly: The Carboranes

March 24, 2009

( -- To be useful in real-world applications, a self-assembled monolayer (SAM) of molecules on a surface must have a stable and controllable geometry. Researchers at Penn State and the Sigma-Aldrich company have ...

Recommended for you

A new form of real gold, almost as light as air

November 25, 2015

Researchers at ETH Zurich have created a new type of foam made of real gold. It is the lightest form ever produced of the precious metal: a thousand times lighter than its conventional form and yet it is nearly impossible ...

New 'self-healing' gel makes electronics more flexible

November 25, 2015

Researchers in the Cockrell School of Engineering at The University of Texas at Austin have developed a first-of-its-kind self-healing gel that repairs and connects electronic circuits, creating opportunities to advance the ...

Getting under the skin of a medieval mystery

November 23, 2015

A simple PVC eraser has helped an international team of scientists led by bioarchaeologists at the University of York to resolve the mystery surrounding the tissue-thin parchment used by medieval scribes to produce the first ...

Atom-sized craters make a catalyst much more active

November 24, 2015

Bombarding and stretching an important industrial catalyst opens up tiny holes on its surface where atoms can attach and react, greatly increasing its activity as a promoter of chemical reactions, according to a study by ...


Adjust slider to filter visible comments by rank

Display comments: newest first

5 / 5 (1) Mar 10, 2011
Love the research, but it's a perfect example of the vanity of the human species - why ignore a billion years of biological engineering? Instead, start with myosin and dynein molecular motors powered by ATP and improve from there....

not rated yet Mar 11, 2011
Maybe this principle could one day replace PV solar panels, if they find more efficient conversion molecules.
not rated yet Mar 12, 2011
Love the research, but it's a perfect example of the vanity of the human species - why ignore a billion years of biological engineering? Instead, start with myosin and dynein molecular motors powered by ATP and improve from there....
The very fact that this system reacts to light is a huge selling point. Motor proteins really don't do that, and they also require supporting mechanisms that produce ATP, transduce signals, and so on.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.