Nanotech News

October 31, 2005

DNA Template Enables Proofreading And Error-Correction In Nanomaterials

By mimicking nature, researchers at the University of Illinois at Urbana-Champaign have developed a procedure that can find and correct defects in self-assembled nanomaterials. The new proofreading and error-removal process uses catalytic DNA and is straightforward enough that it could provide a new approach for making nanoparticles with carefully controlled physical characteristics. The ability to produce well-defined nanoparticles could prove to be an important consideration for securing regulatory approval for nanoparticle-based cancer therapeutics and imaging agents.

Despite much progress made in the self-assembly of nanomaterials, defects that occur during the assembly process still present major obstacles for applications such as molecular electronics and photonics. Efforts to overcome this problem have focused on optimizing the assembly process to minimize errors, and designing devices that can tolerate errors.

"Instead of trying to avoid defects or work around them, it makes more sense to accept defects as part of the process and then correct them during and after the assembly process," said Yi Lu, Ph.D., who led the University of Illinois team. "This procedure is analogous to how nature deals with defects, and can be applied to the assembly of nanomaterials using biomolecules."

In protein synthesis, nature ensures accuracy by utilizing a proofreading unit that detects and corrects errors in translating genetic information into a protein’s composition. In a similar fashion, Dr. Lu and his colleagues utilized catalytic DNA to locate and remove errors in a gold nanoparticle assembly process. The researchers describe the procedure in a paper published in the journal Angewandte Chemie International Edition.

Catalytic DNA contains two segments – a “substrate” strand and an enzyme strand. In the presence of certain ions, the substrate is cleaved by the enzyme into two pieces of unequal length. The cleaved fragment with the shorter binding arm can be easily released. This catalytic DNA serves as a template assembling nanoparticles of consistent size.

When a particle of the correct size is encountered, binding of the longer arm of the enzyme to the DNA template occurs, while binding of the shorter arm to the DNA template is inhibited. "The active structure of the catalytic DNA cannot form," Dr. Lu said. "As a result, the template is not cleaved and the particle is incorporated into the assembly."

When a particle of the wrong size is mistakenly incorporated into the assembly, the enzyme can bind both its arms to the substrate template and form an active structure to cleave the substrate and remove the particle. By showing that defects - the wrong size particles, in this case - can be identified and removed, the researchers demonstrated that proofreading and error-correction can take place during and after the assembly of nanoparticles.

"This was a small, but definite, step in the right direction," Dr. Lu said. "The error-correction procedure can be expanded to include many other biomolecules compounds for controlling the assembly of nanoparticles of defined particle sizes, shapes or compositions; as well as other nanomaterials, such as nanotubes and nanowires."

This work is detailed in a paper titled, “Proofreading and error removal in a nanomaterial assembly.” This paper was published online in advance of print publication. An abstract is available through the journal’s website.
View abstract.