 Silver nanoparticles are one of nanotechnology's commercial success stories and lend their anti-bacterial properties to a number of consumer products from white goods to socks. Scientists from Banaras Hindu University, India, have taken up the challenge to find out more about what makes silver nanoparticles so special. Using a colorimeter set-up to examine the effect of silver nanoparticles on bacterial growth rates, the team has discovered that silver nanoparticles are more aggressive towards gram-negative bacteria, which include Escherichia coli, Salmonella and Hemophilus influenzae compared with gram-positive organisms. The group took electron micrographs to study the mechanism in greater detail. "Initially, clusters of nanoparticles were seen to anchor to the bacterial cell wall, possibly at sites that are rich in negatively charged functional groups," Debabrata Dash from the university's institute of medical sciences told nanotechweb.org. "Later, the nanoparticles managed to enter the cell and make perforations in the membrane, which could result in cell lysis [breakdown]." Gram-negative bacteria have a cell wall that measures just 7–8 nm and are covered in a layer of lipopolysaccharides that lacks strength and rigidity. Gram-positive bacteria, on the other hand, are more robust and feature a 20–80 nm thick cell wall that is much harder for silver nanoparticles to penetrate. The team thinks that medicine and bioengineering will ultimately be the big beneficiaries. "It appears that bacteria exhibit no resistance to silver nanoparticles, which makes the treatment a promising alternative to conventional antibiotics," said Debabrata Dash. "In addition, the cost, the synthesis and the preservation of silver nanoparticles is likely to be far cheaper and simpler than any conventional drug." The researchers presented their work in Nanotechnology. James Tyrrell is editor of nanotechweb.org.
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