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Lausanne, Switzerland (SPX) Sep 14, 2012
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 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. The system is outlined in an article appearing September 9, 2012 in the journal Nature Materials.
Methyl mercury, toxic and difficult to monitor
"The problem is that current monitoring techniques are too expensive and complex," explains Constellium Chair holder at EPFL and co-author Francesco Stellacci. "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." But industrial discharge fluctuates.
A simple, inexpensive new technology
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," explains 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," notes Stellacci.
Convincing tests in Lake Michigan and Florida
A mosquito fish from the Everglades in Florida was also tested. This species is not very high on the food chain and thus does not accumulate high levels of mercury in its tissues. "We measured tissue that had been dissolved in acid. The goal was to see if we could detect even minuscule quantities." says Bartosz Grzybowski, Burgess Professor of Chemistry and Director of Non-Equilibrium Energy Research Center at Northwestern University. The United States Geological Survey reported near-identical results after analyzing the same sample.
From quantum to real applications
"With this technology, it will be possible to conduct tests on a much larger scale in the field, or even in fish before they are put on the market," says lead author Eun Seon Cho. This is a necessary public health measure, given the toxic nature of methyl mercury and the extremely complex manner in which it spreads in the environment and accumulates in living tissues.
Ecole Polytechnique Federale de Lausanne
Space Technology News - Applications and Research
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