While progress has been made in reducing the amount of heavy metal pollution, the very nature of heavy metal contamination means it continues to be a problem in waterways around the world. Conventional heavy metal contamination detection methods require sending samples off to a lab for analysis on expensive equipment. Now a Swiss-American team has developed a cheap way to immediately ascertain the levels of heavy metals in lakes and rivers and the fish pulled out of them.
The team, led by Francesco Stellacci at the Ecole Polytechnique Fédérale de Lausanne (EPFL) and Bartosz Grzybowski at Northwestern University, has developed what it dubs a kind of “nano-velcro.” The technology consists of a strip of glass covered in a film of nanoparticles that are themselves covered with tiny hairs. When an ion (positively charged particle), such as a methyl mercury or cadmium ion, comes into contact with these hairs, they close up to trap the particle.
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The number of trapped particles, and therefore the level of heavy metal contamination, can be calculated by measuring the voltage across the nanostructure. This is because the more ions that are trapped in the nano-velcro, the more electricity it will conduct. The nano-velcro can also be made to target particular kinds of pollutants by varying the length of the tiny hairs. The researchers say they have already demonstrated the detection of mercury and cadmium with very high sensitivity.
Stellacci says because the most common form of mercury, methyl mercury, has properties that make it easy to trap without accidentally trapping other substances, the technology is very accurate and reliable. In tests in Lake Michigan, results obtained using the new system were comparable to measurements taken by the FDA using conventional techniques.
To assess the sensitivity of the technology, the team also conducted tests on a mosquito fish from the Florida Everglades. Because this species isn’t very high on the food chain, it doesn’t 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 Grzybowski. The nano-velcro technology gave near-identical results to those reported by the U.S. Geological Survey after analyzing the same sample.
Importantly, the nano-velcro technology is far cheaper than conventional heavy metal measurement techniques. The researchers say the “reading” glass strip could potentially cost less than US$10, while the voltage-measuring device would cost only a few hundred dollars. It also offers much greater convenience, with analysis able to be carried out in the field and results available immediately.
“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.
The team’s study appears in the journal Nature Materials.