Economic method measures toxic metals in fluids

A strip of glass covered in nanoparticles can cheaply and conveniently measure mercury and other toxic metals in fluids.

According to a statement, researchers at the Swiss Federal Institute of Technology (EPFL), Northwestern University and the University of Michigan found that their new method can measure methyl mercury, the most common form of mercury pollution, at unprecedentedly small concentrations.

The system, which could test for metal toxins in drinking water and fish, is reported in the current edition of Nature Materials.

Methyl mercury dumped in lakes and rivers accumulates in fish, reaching its highest levels in large fish such as tuna and swordfish. Young children and pregnant women are advised to avoid eating these fish because mercury can affect the developing brain and nervous system. While metals in drinking water are measured periodically, these measurements say little about migratory fish, including tuna, which may pass through more polluted areas.

‘The problem is that current monitoring techniques are too expensive and complex,’ said Francesco Stellacci, the Constellium chair holder at EPFL. ‘With a conventional method, you have to send samples to the laboratory, and the analysis equipment costs several million dollars.’

Using the device invented by the Swiss-US team, measuring the mercury levels in water or dissolved fish meat is claimed to be as simple as dipping a strip of coated glass into the fluid.

Metals and metallic molecules, such as methyl mercury, typically become positively charged ions in water. When these ions drift between so-called ‘hairy’ nanoparticles, the hairs close up, trapping the pollutant. Passing a current over the strip of glass reveals how many ions are caught in the ‘nano-velcro.’ Each ion allows the strip to conduct more electricity.

U-M researchers Hao Jiang and Sharon Glotzer, the Churchill professor of chemical engineering, performed computer simulations that investigated how the nano-velcro traps pollutants. They showed that the hairy nanoparticles are selective about which ions they capture, confirming that the strips can give reliable measures of specific toxins as demonstrated by the experimental findings of the Swiss group.

The scientists targeted particular pollutants by varying the length of the nano-hairs. This approach is said to be especially successful for methyl mercury, and the device can measure it with heightened accuracy, detecting concentrations as low as 600 methyl mercury ions per cubic centimetre of water.

The researchers estimate that the coated glass strips could cost less than $10 (£6) each, while the measurement device will cost only a few hundred dollars, gauging the concentration of metals onsite and within minutes.