New device can detect toxic metals in water

Researchers from the Northwestern University and colleagues at Ecole Polytechnique Federale de Lausanne (EPFL) in Switzerland created a device that can detect very small amounts of mercury in polluted water.

When mercury is dumped into rivers and lakes, the toxic heavy metal can end up in the fish and water.

"The system currently being used to test for mercury and its very toxic derivative, methyl mercury, is a time-intensive process that costs millions of dollars and can only detect quantities at already toxic levels," said Bartosz Grzybowski, lead author of the study.

"Ours can detect very small amounts, over million times smaller than the state-of-the-art current methods. This is important because if you drink polluted water with low levels of mercury every day, it could add up and possibly lead to diseases later on. With this system consumers would one day have the ability to test their home tap water for toxic metals," Grzybowski said in a statement.

The new system comprises a commercial strip of glass covered with a film of 'hairy' nanoparticles, a kind of a 'nano-velcro', that can be dipped into water.

When a metal cation - a positively charged entity, such as a methyl mercury - gets in between two hairs, the hairs close up, trapping the pollutant and rendering the film electrically conductive.

A voltage-measuring device reveals the result; the more ions there are trapped in the 'nano-velcro', the more electricity it will conduct.

To calculate the number of trapped particles, the voltage across the nanostructure film can be measured.

By varying the length of the nano-hairs covering the individual particles in the film, the scientists can target a particular kind of pollutant that is captured selectively.

With longer 'hairs', the films trap methyl mercury, shorter ones are selective to cadmium. Other metals also can be selected with appropriate molecular modifications.

"The nanoparticle films cost somewhere between USD 1 to USD 10 to make, and the device to measure the currents costs a few hundred dollars," Grzybowski said.

The study was published in the journal Nature Materials.