February 28, 2005
Purdue researchers use enzyme to clip 'DNA wires'
WEST LAFAYETTE, Ind. Researchers at Purdue University have attached magnetic "nanoparticles" to DNA and then cut these "DNA wires" into pieces, offering the promise of creating low-cost, self-assembling devices for future computers.
Findings are detailed in a paper published online in February in the Journal of the American Chemical Society. The paper was written by Purdue graduate student Joseph M. Kinsella and Albena Ivanisevic, an assistant professor of biomedical engineering and chemistry at Purdue.
DNA, or deoxyribonucleic acid, has an overall negative charge, so it might be used in a process called self-assembly to create electronic devices. When placed in a solution with magnetic particles that have a positive charge, the particles are automatically attracted to the DNA strands, which act as tiny scaffolds for creating wires.
Other researchers have "metalized" DNA by coating it with copper, gold and platinum, but no other researchers have coated DNA and then cut the strands into smaller pieces using a "restriction enzyme," a class of enzyme that causes DNA to fragment, Kinsella said.
Because magnetic components are essential for today's computer memory, the findings represent potential future applications for DNA-based structures in computers created with "molecular electronics," in which biological molecules might be harnesses to create devices for computers, sensors and other uses. Self-assembly might be used in the future to create electronic devices at lower cost than is possible with conventional manufacturing processes.
Purdue researchers had previously developed a technique for precisely placing strands of DNA on a silicon chip and then stretching out the strands so that their encoded information might be read more clearly. The current work by Ivanisevic's team builds on that previous research.
Kinsella created the magnetic particles, which are made from a ceramic iron oxide material about 4 nanometers in diameter. A nanometer is one billionth of a meter, or roughly 10 times the size of a hydrogen atom.
The Purdue researchers sliced the DNA wires with an enzyme called BamH1, one of numerous restriction enzymes that are used in standard genetic engineering techniques to snip DNA so that scientists can alter the genetic structures of organisms like bacteria.
DNA molecules contain "bases" called guanine, adenine, thymine and cytosine, represented as G, A, T and C. The bases combine in numerous sequences, and various restriction enzymes attach to and cut specific sequences, enabling scientists to isolate and snip DNA segments of differing lengths. The enzyme used in the Purdue research cuts segments of DNA containing a sequence of GGATCC.
"We incubate the particles and DNA in a solution, and the electric charge brings them together to form the wire," Ivanisevic said. "Then we basically make smaller wire segments with magnetic particles attached to this DNA sequence."
Because hundreds of different restriction enzymes snip segments containing specific sequences of genetic material, the method might be used in the future to cut DNA wires of varying lengths for building electronic devices.
Ivanisevic and former Purdue physics graduate student Dorjderem Nyamjav were the first to coat DNA with magnetic particles two years ago. Kinsella and Ivanisevic are the first to show that the BamH1 enzyme cuts DNA wires.
"We weren't sure the enzyme would be able to recognize the DNA sequence covered with particles," Kinsella said. "We thought the particles might hinder the process."
The researchers found, however, that the particles did not interfere with the process, possibly because the electrical charges are strong enough to hold the particles firmly in place, but weak enough to enable the enzyme to push them out of the way.
"The entire strand of DNA used in this research has been stretched onto silicon oxide surfaces at lengths up to 35 microns, or millionths of a meter, and 2 nanometers wide," Kinsella said. "When coated with particles and fragmented by the enzyme, we were able to distinguish that the once-single DNA wire was clipped into smaller wires."
In future work, the Purdue researchers plan to stretch DNA coated with magnetic particles between electrodes and test the coated genetic material for electrical properties.
The research is funded by the National Aeronautics and Space Administration through Purdue's NASA Institute for Nanoelectronics and Computing. The institute is a collaboration of six universities led by Purdue, whose director is Supriyo Datta, the Thomas Duncan Distinguished Professor of Electrical and Computer Engineering at Purdue. The work also is affiliated with the Birck Nanotechnology Center and the Bindley Bioscience Center in Purdue's Discovery Park, the university's hub for high-tech research.
Writer: Emil Venere, (765) 494-4709, firstname.lastname@example.org
Sources: Joseph Kinsella, (765)496-6431, email@example.com
Albena Ivanisevic, (765) 496-3676, firstname.lastname@example.org
Purdue News Service: (765) 494-2096; email@example.com
Note to Journalists: An electronic or hard copy of the research paper is available from Emil Venere, (765) 494-4709, firstname.lastname@example.org.
Part A of this graphic shows a procedure for "templating" magnetic iron oxide nanoparticles onto DNA and stretching the DNA using a technique called molecular combing. Part B is an image taken with an atomic force microscope that shows a DNA strand coated with magnetic iron oxide nanoparticles. Researchers at Purdue University have shown how to attach the nanoparticles to DNA and use a "restriction enzyme" to cut the resulting "DNA wires" into pieces, offering the promise of creating low-cost, self-assembling devices for future computers. (Purdue University, Weldon School of Biomedical Engineering.)
A publication-quality graphic is available at http://ftp.purdue.edu/pub/uns/+2005/Ivanisevic.DNAwires.jpg
Enzymatic Clipping of DNA Wires Coated
aWeldon School of Biomedical Engineering,
bDepartment of Chemistry, Purdue University
The study describes how DNA coated with magnetic nanoparticles remains biologically active and accessible to the BamH1 restriction enzyme. Long DNA molecules are coated with magnetic nanoparticles using electrostatic interactions. The coated, stretched and surface-bound DNA is incubated in the restriction enzyme that specifically recognizes any strand containing the GGATCC base sequence and clips the DNA. We show that despite the presence of the nanoparticles on the DNA, the enzyme is still able to recognize the cleavage site and effectively digest the assembly.
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