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Ions, not particles, make silver toxic to bacteria
Date:7/11/2012

HOUSTON (July 11, 2012) Rice University researchers have settled a long-standing controversy over the mechanism by which silver nanoparticles, the most widely used nanomaterial in the world, kill bacteria.

Their work comes with a Nietzsche-esque warning: Use enough. If you don't kill them, you make them stronger.

Scientists have long known that silver ions, which flow from nanoparticles when oxidized, are deadly to bacteria. Silver nanoparticles are used just about everywhere, including in cosmetics, socks, food containers, detergents, sprays and a wide range of other products to stop the spread of germs.

But scientists have also suspected silver nanoparticles themselves may be toxic to bacteria, particularly the smallest of them at about 3 nanometers. Not so, according to the Rice team that reported its results this month in the American Chemical Society journal Nano Letters.

In fact, when the possibility of ionization is taken away from silver, the nanoparticles are practically benign in the presence of microbes, said Pedro Alvarez, George R. Brown Professor and chair of Rice's Civil and Environmental Engineering Department.

"You would be surprised how often people market things without a full mechanistic understanding of their function," said Alvarez, who studies the fate of nanoparticles in the environment and their potential toxicity, particularly to humans. "The prefix 'nano' can be a double-edged sword. It can help you sell a product, and in other cases it might elicit concerns about potential unintended consequences."

He said the straightforward answer to the decade-old question is that the insoluble silver nanoparticles do not kill cells by direct contact. But soluble ions, when activated via oxidation in the vicinity of bacteria, do the job nicely.

To figure that out, the researchers had to strip the particles of their powers. "Our original expectation was that the smalle
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Contact: Mike Williams
mikewilliams@rice.edu
713-348-6728
Rice University
Source:Eurekalert  

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Ions, not particles, make silver toxic to bacteria
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