Deadly nanocarpet
27 Sep 2004
University of Pittsburgh researchers have created a 'nanocarpet ' of nanotubes that not only displays sensitivity to different chemical agents by changing colour, but can also be 'trained' to kill bacteria.
The researchers, led by Dr. Alan J. Russell, professor of surgery at the University of Pittsburgh School of Medicine, 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 colours when appropriately formulated) they could create a molecule which would act as both a biosensor and biocide.
Remarkably, in addition to being able to kill cells, the resulting reaction mixture had the ability to self assemble into a nanocarpet of nanotubes of uniform structure as well.
To test the nanostructure's potential as a biosensor and antimicrobial, the researchers conducted studies using the water-based nanotubes.
Normally a neutral colour, when exposed to ultraviolet light, the nanotubes changed to a permanent deep blue. The process also chemically altered the nanotubes so that they became polymerised, giving them a more firm structure. Polymerised, these nanotubes could change from blue to other colours, depending on their exposure to different materials. For instance, in tests with acids and detergents, they turned red or yellow.
The most critical tests, say the researchers, were those involving E. coli, which were conducted to assess the material's interactions with living cells. In the presence of E. coli, some strains of which are food-borne pathogens, the nanotubes turned shades of red and pink. Moreover, with the aid of an electron microscope, the researchers observed the nanotubes piercing the membranes of the bacteria like a needle being inserted into the cell. Both the polymerised and the unpolymerised nanotube structures were effective antimicrobials, completely killing all the E. coli within an hour's time.
The research, funded by the US 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 colour and simultaneously destroy the deadly substances.
