Nov 26, 2013 |
Germ-killing black silicon, a synthetic nanomaterial, opens up new front in hygiene
|
(Nanowerk News) Imagine a hospital room, door handle or kitchen countertop that is free from bacteria — and not one drop of disinfectant or boiling water or dose of microwaves has been needed to zap the germs.
That is the idea behind a startling discovery made by scientists in Australia.
|
In a study published on Tuesday in the journal Nature Communications ("Bactericidal activity of black silicon"), they described how a dragonfly led them to a nano-tech surface that physically slays bacteria.
|
The germ-killer is black silicon, a substance discovered accidentally in the 1990s and now viewed as a promising semiconductor material for solar panels.
|
Under an electron microscope, its surface is a forest of spikes just 500 nanometres (500 billionths of a metre) high that rip open the cell walls of any bacterium which comes into contact, the scientists found.
|
It is the first time that any water-repellent surface has been found to have this physical quality as bactericide.
|
Last year, the team, led by Elena Ivanova at Swinburne University of Technology in Melbourne, were stunned to find cicada wings were potent killers of Pseudomonas aeruginsoa — an opportunist germ that also infects humans and is becoming resistant to antibiotics.
|
Looking closely, they found that the answer lay not in any biochemical on the wing, but in regularly-spaced “nanopillars” on which bacteria were sliced to shreds as they settled on the surface.
|
They took the discovery further by examining nanostructures studding the translucent forewings of a red-bodied Australian dragonfly called the wandering percher (Latin name Diplacodes bipunctata).
|
It has spikes that are somewhat smaller than those on the black silicon — they are 240 nanometres high.
|
The dragonfly’s wings and black silicon were put through their paces in a lab, and both were ruthlessly bactericidal.
|
Smooth to the human touch, the surfaces destroyed two categories of bacteria, called Gram-negative and Gram-positive, as well as spores, the protective shell that coats certain times of dormant germs.
|
The three targeted bugs comprised P. aeruginosa, the notorious Staphylococcus aureus and the ultra-tough spore of Bacillus subtilis, a wide-ranging soil germ that is a cousin of anthrax.
|
The killing rate was 450,000 bacterial cells per square centimetre per minute over the first three hours of exposure.
|
This is 810 times the minimum dose needed to infect a person with S. aureus, and a whopping 77,400 times that of P. aeruginosa.
|
If the cost of making black silicon is an obstacle, many other options are around for making nano-scale germ-killing surfaces, said the scientists.
|
“Synthetic antibacterial nano-materials that exhibit a similar effectiveness... can be readily fabricated over large areas,” they wrote.
|