Printing with enzymes
Researchers at Duke University have developed a new printing technique using catalysts to create microdevices such as labs-on-a-chip. Their inkless printing technique uses enzymes from E. coli bacteria and has an accuracy of less than 2 nanometers. While they're are now using enzymes to stamp nanopatterns without ink, the research team is already working with non-enzymatic catalysts. And it added that 'future versions of the inkless technique could be used to build complex nanoscale devices with unprecedented precision.'
You can see above a not-to-scale graphic showing "how catalyst (blue hollow-ended beads) dangles from patterned stamp, while dye particles (gold balls) are bonded to DNA chains to make DNA coating visible. After stamp (blue) presses into DNA coating (yellow) at center the catalyst detaches dye and DNA chain's tip (bottom right). That disruption creates patterning in DNA coating (top right)." (Credits: graphic by Alexander Shestopalov, caption by Duke University) Here is a link to a larger version of this graphic.
This project has been led by Robert Clark, Thomas Lord Professor and acting dean of Duke University's Pratt School of Engineering, and by Eric Toone, Professor of Chemistry and Professor of Biochemistry, and several members of his research group.
Microcontact printing is not new, so what did bring the researchers to the field? "In traditional microcontact printing -- also called soft lithography or microstamping -- an elastic stamp's end is cast from a mold created via photolithograpy – a technique used to generate microscopic patterns with light. Those patterns are then transferred to a surface by employing various biomolecules as inks, rather like a rubber stamp." [But] "a shortcoming of traditional microcontact printing is that pattern transfer relies on the diffusion of ink from the stamp to the surface. This same diffusion spreads out beyond the limits of the pattern as the stamp touches the surface, degrading resolution and blurring the feature edges, Clark and Toone said."
And how did they prove their solution was working? "In lieu of ink, [the researchers] suspended a biological catalyst on the stamp with a molecular 'tether' of amino acids. For this proof-of-principle demonstration, Toone's team chose as a catalyst the biological enzyme exonuclease I, derived from the bacterium E. coli. In one set of experiments, the polyacrylamide stamp pattern bearing the tethered enzymes was then pressed on a surface of gold that had been covered with a uniform coating of single-stranded DNA molecules. The DNA molecules had also been linked to fluorescent dye molecules to make the coating visible under a microscope. Wherever the enzyme met the DNA, the end of the DNA chain and its attached dye were broken off and removed. That created a dye-less pattern of dots on the DNA coating, each dot measuring about 10 millionths of a meter diameter each.
For more information, this research work has been published in the Journal of Organic Chemistry under the name "Biocatalytic Microcontact Printing" (Volume 72, Number 19, Pages 7459-7461, September 14, 2007) Here are two links to the abstract and to the full paper (PDF format, 3 pages, 129 KB).
Sources: Duke University news release, via EurekAlert!, September 27, 2007; and various websites
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