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Nanotubes Made That Detect and Kill Biological Agents PITTSBURGH, Pennsylvania, September 27, 2004 (ENS) - University of Pittsburgh researchers have built a simple molecule that produces uniform, self-assembled nanotubes - miniscucle structures about one ten-thousandth the width of a human hair - that display sensitivity to different agents by changing color and can be trained to kill bacteria. Their findings demonstrate a way to develop paints that can simultaneously detect and kill biological weapons. "In these nanotube structures, we have created a material that has the ability to sense their environment. The work is an outgrowth of our interest in developing materials that both sense and decontaminate chemical or biological weapons," said senior author Alan J. Russell, Ph.D., professor of surgery at the University of Pittsburgh School of Medicine and director of the university's McGowan Institute for Regenerative Medicine.
Alan J. Russell, Ph.D., professor of surgery at the University of Pittsburgh School of Medicine and director of the university's McGowan Institute for Regenerative Medicine. (Photo courtesy McGowan)The research, funded by the U.S. Department of Defense's Army Research Office, has as its goal the development of a paint that in the event of biological or chemical agents being deployed would change color and simultaneously destroy the deadly substances.How a single-step synthesis of a hydrocarbon and a simple salt compound produced these unique nanotube structures with antimicrobial capability is described in a paper posted on the website for the "Journal of the American Chemical Society." The researchers thought that by combining a chemical structure called a quarternary ammonium salt group, known for its ability to disrupt cell membranes and cause cell death, with a hydrocarbon diacetylene, which can change colors, the resulting molecule would have the desired properties of both biosensor and biocide. It turned out that in addition to being able to kill cells, the resulting reaction mixture had the ability to self assemble into "beautiful nanotubes of uniform structure," the researchers said.
Self-Assembling nanotubes in water (Photos courtesy UPMC)When dried from water and other solvents, and under magnification, these nanostructures look much like a heaping serving of macaroni.When "coaxed with simple processing," the researchers said, "the tubes align into the more formal pattern of a nanocarpet." A backing, also self-assembled from the same material, holds it together. The nanocarpet measures about one micrometer in height, approximately the same height as the free-form nanotubes. "This alignment of nanotubes in the absence of a template is an accomplishment that has eluded researchers," said Dr. Russell, who also is a professor of chemical and bioengineering at the University of Pittsburgh School of Engineering.
Self-assembling nanocarpet about micrometer in heightIn their search for what was forming the tubes, the researchers discovered that synthesis of a secondary salt and diacetylene created a lipid molecule, and also resulted in the production of pure self-assembling nanotubes, all having the same diameter, 89 nanometers, and wall thickness, 27 nanometers.By comparison, a human hair is about 1,000 times wider. "To our knowledge, the remarkable self-assembly of this inexpensive and simple lipid is unprecedented and represents an important step toward rational design of bioactive nanostructures," explained Sang Beom Lee, Ph.D., research assistant professor of bioengineering in the School of Engineering, who is listed as first author. Because the nanotubes form within hours at room temperature, the costs of synthesizing carbon nanotubes can be reduced, he said. To test the nanostructure's potential as a biosensor and antimicrobial, the authors conducted studies using the water-based nanotubes. Normally a neutral color, when exposed to ultraviolet light the nanotubes changed to a permanent deep blue. The process also chemically altered the nanotubes so that they became polymerized, giving them a more firm structure. Polymerized, these nanotubes could change from blue to other colors, depending on its exposure to different materials. For instance, in tests with acids and detergents, they turned red or yellow.
Nanotube piercing E.coli bacteriaThe most critical tests, say the researchers, were conducted to assess the material's interactions with living cells. The nanotubes were tested on the bacteria E. coli, some strains of which are food borne pathogens.In the presence of E. coli, the nanotubes turned shades of red and pink. Moreover, with the aid of an electron microscope, the researchers observed the tubes piercing the membranes of the bacteria like a needle being inserted into the cell. Both the polymerized nanotube structures that can change color and the unpolymerized nanotube structures were effective antimicrobials, completely killing all the E. coli within an hour's time. "We are very encouraged by these results and we will be continuing our investigations of this novel material in collaboration with our colleagues here at the University of Pittsburgh and the U.S. Army Research Office," said Dr. Russell. photo McGowan http://www.mirm.pitt.edu/people/faculty_staff.html |
