A new filter needs only gravity and a weak electric current to produce its sterilising effect, making it suitable for a portable water-treatment device.
The fabric is easy to produce, says lead researcher Yi Cui at Stanford University in California. Cui's team simply dip a piece of cotton into a solution of CNTs and then pipette droplets containing silver nanowires onto the cotton.
|Prepare to die, E. coli (Image: Linda Stannard/UCT/SPL)|
Analysing the fabric with a scanning electron microscope reveals that the CNTs stick to the individual cotton fibres, while the slightly larger silver nanowires form a mesh between the fibres. The nanoparticles enable the fabric to conduct electricity, so a weak electric current can run across it. This helps kill bacteria by damaging their outer membranes, while the silver nanowires' anti-bacterial properties do the rest.
So when Cui and his colleagues poured water contaminated with the bacterium Escherichia coli (pictured) through the silver-coated, electrically-conducting fabric, they found it killed 89 per cent of the bacteria. By conducting three successive runs through the fabric, they were able to kill over 98 per cent - enough to make the water safe to drink (Nano Letters, DOI: 10.1021/nl101944e).