University of Houston researchers have found that mixing carbon nanotubes with a particular polymer can boost their bactericidal action in thin films.
Carbon nanotubes can kill bacteria and prevent the formation of virulent and corrosive biofilms, probably by puncturing the microbes’ cell walls. As a result, scientists think the nanomaterials could produce antimicrobial coatings for surgical equipment and industrial piping. However, nanotubes are difficult to turn into effective coatings, toxic to people at high concentrations, and expensive. Now researchers led by Debora F Rodrigues at the University of Houston report that mixing nanotubes with a specific polymer can produce thin films that are still effective at killing bacteria, but use very low concentrations of nanotubes. The results are reported in the journal Environmental Science and Technology. When mixed into a solvent or applied to a surface alone, carbon nanotubes tend to clump together. These nanotube clumps produce uneven coatings and have relatively small surface areas exposed to the environment, decreasing their ability to kill microbes. Previous research showed that mixing nanotubes with polymers could help break up these clumps. The Rodrigues team wanted to know what proportion of nanotubes they needed to add to such a mixture to retain the nanotubes’ antimicrobial properties. They chose the polymer called polyvinyl-N-carbazole, because they could easily use it to form thin films on metal surfaces through electrodeposition. They tested a mixture of 3% nanotubes with 97% polymer by weight. In a liquid suspension containing the nanotube-polymer composite along with Escherichia coli and Bacillus subtilis cells, the nanotubes damaged or killed 94% of the E. coli and 90% of the B. subtilis. When they used the mixture to produce a thin film, the scientists found that it completely inhibited the formation of biofilms on the metal surface. The nanotube-polymer mix also killed up to 90% of both species of bacteria added to the surface, about the same effect as that produced by a coating of carbon nanotubes alone.