Nano-velcro detects traps toxic pollutant

Nano-velcro detects and traps toxic pollutant

9:35 AM, 10th September 2012
Nano-velcro detects and traps toxic pollutant
Researchers develop nano-strips for inexpensive testing of mercury levels in our lakes and oceans with unprecedented sensitivity.

LAUSANNE, SWITZERLAND: Mercury, when dumped in lakes and rivers, accumulates in fish, and often ends up on our plates. A Swiss-American team of researchers led by Francesco Stellacci, Constellium Chair holder at the Ecole Polytechnique Federale de Lausanne (EPFL) and Bartosz Grzybowski at Northwestern University has devised a simple, inexpensive system based on nanoparticles, a kind of nano-velcro, to detect and trap this toxic pollutant as well as others. The particles are covered with tiny hairs that can grab onto toxic heavy metals such as mercury and cadmium.

This technology makes it possible to easily and inexpensively test for these substances in water and, more importantly, in the fish that we eat. Their new method can measure methyl mercury, the most common form of mercury pollution, at unprecedentedly small attomolar concentrations. Researchers are particularly interested in detecting mercury. Its most common form, methyl mercury, accumulates as one goes up the food chain, reaching its highest levels in large predatory fish such as tuna and swordfish.

“The problem is that current monitoring techniques are too expensive and complex. We periodically test levels of mercury in drinking water, and if those results are good, we make the assumption that levels are acceptable in between those testing periods,” explained Stellacci.

The technology developed by the Swiss-American team is simple to use. A strip of glass covered with a film of ‘hairy’ nanoparticles is dipped into the water. When an ion - a positively charged particle, such as a methyl mercury or cadmium ion - gets in between two hairs, the hairs close up, trapping the pollutant. A voltage-measuring device reveals the result; the more ions there are trapped in the nano-velcro, the more electricity it will conduct. So to calculate the number of trapped particles, all one needs to do is measure the voltage across the nanostructure.

By varying the length of the nano-hairs, the scientists can target a particular kind of pollutant. “The procedure is empirical,” explained Stellacci. Methyl mercury, fortunately, has properties that make it extremely easy to trap without accidentally trapping other substances at the same time; thus the results are very reliable.

The interesting aspect of this approach is that the ‘reading’ glass strip could costs less than 10 dollars, while the measurement device will cost only a few hundreds of dollars. The analysis can be done in the field, so the results are immediately available. “With a conventional method, you have to send samples to the laboratory, and the analysis equipment costs several million dollars,” said Stellacci.

“I think it is quite incredible, how the complex principles of quantum tunneling underlying our device translate into such an accurate and practically useful device. It is also notable that our system - through some relatively simple chemical modifications - can be readily adapted to detect other toxic species,” said Grzybowski.

© EPFL News

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