Single carbon nanotubes prick bacteria to death: Carbon Nanotubes

Abstract

VOLUME 12 – ELECTRON MICROSCOPY SPECIAL ISSUE 9 Single walled carbon nanotubes (SWCNTs) have recently been in the spotlight because of their apparent toxicity to bacteria, triggering further research into their properties and the effects on health and the environment. Now researchers from the Nanyang Technological University of Singapore have discovered that SWCNTs are far more toxic towards bacteria as individual entities than when they are clustered together as aggregates [Liu et al., ACS Nano (2009) doi: 10.1021/nn901252r]. The team led by Yuan Chen found that individual SWCNTs act as tiny darts, repeatedly pricking bacterial cell membranes as they move around in a saline solution. Experiments show that it is purely this pricking or dartlike action of the fast moving SWCNTs which affects bacterial cellular activity and not cell growth inhibition, oxidative stress, or the Co catalyst residue left over from SWCNT fabrication. The antibacterial properties of SWCNTs increase on further dispersion and with increased concentration of single SWCNTs, while actions that speed up SWCNT movement in solution improve the antibacterial nature of SWCNTs. In addition to this, atomic force microscopy studies of a suspension of SWCNTs and bacteria in saline indicate a strong correlation between cell death and mechanical properties such that softer cells are more vulnerable to piercing and death than bacteria with tougher membranes. Chen describes the difficulties encountered in the run-up to this discovery. “One of major challenges in carbon nanotube toxicity study is the heterogeneous nature of current available nanotube samples due to the coexistence of many species. We previously developed novel catalysts to produce SWCNTs with a narrow structure distribution and a facile centrifugation-based purification protocol which provides samples containing a controllable amount of impurities,” he explains. “These allow us to look into the SWCNT antibacterial activity in a systematic way.” These studies are of importance in developing strategies for the future use of SWCNTs as Chen tells Materials Today. “In nanomedicine, we should enhance their [SWCNTs] antibacterial activity (or toxicity) in fighting bacteria or diseases by dispersing them individually, increasing concentration and elevating their mobility. If we want to minimize their health and environmental risks, we should keep them immobilized, or even trap them in a soft polymer shell.” Katerina Busuttil Single carbon nanotubes prick bacteria to death