Colourful detection crystals

A group of Australian researchers have found a fast method of detecting toxins produced from pesticides and chemical weapons.

The research, published in the journal ACS Nano, explains how perovskite nanocrystals – which were being used to develop new solar panels – can also change colour in the presence of methyl iodide.

Methyl iodide is a colourless, odourless chemical used in pesticides and fungicides. In large amounts, it can be harmful to people and the atmosphere (it degrades the ozone layer).

Previously, the only methods we had of detecting methyl iodide required expensive laboratory equipment, making it difficult to tell when it was reaching dangerous levels.

But these crystals react with the methyl iodide quickly – exchanging bromine with the iodine in the molecule. This makes the crystals change colour, from green through to yellow, and then deep red.

Most usefully, the change in colour is dependent on the concentration of methyl iodide.

“Perovskite nanocrystals have proved to be a very efficient light emitter,” says lead author Wenping Yin, a researcher at Monash University.

“Here we showed that methyl iodide can react with such perovskites, and do so very quickly following a simple chemical activation step. Critically, this activation step cuts the response time of the sensor from a few hours to just a few seconds.”

“Although the chemical mechanism is very complicated, the outcome is just a colour change of the light produced by the nanocrystals, which is very easy to detect.”

Senior author Jacek Jasieniak, a professor at the ARC Centre for Excellence in Exciton Science, says the technique could also be adapted to detect toxins from chemical warfare, like mustard gas or tear gas.

“It needs further development to realise its true potential for broader detection of different types of methyl halide species, as well as pesticides and chemical warfare agents, like teargas, and mustard gas, but the stage is set.”

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