Researchers have developed a new inexpensive breathalyser which changes colour from green to red with higher alcohol concentrations to catch those who have been drinking and driving.
Most breathalysers are expensive and unable to test for precise concentrations of alcohol, researchers said.
Unlike current colour change-based devices, the new sensor can be reused and could also provide a precise digital readout.
The new design is the first to use the sensing properties of opals, a type of gemstone, to detect the gas version of ethanol, the intoxicating component of commercial liquor, by inducing a change in colour that is visible to the human eye.
The portable breathalysers preferred by roadside police use expensive electronic readouts, but these devices lack the "immediate and intuitive" colour change that tells them whether the alcohol content of a suspect's breath puts them in the legal red zone, said first author Riccardo Pernice of the Universita degli Studi di Palermo in Italy.
Techniques that do use colour change to assess the level of alcohol concentration are typically less expensive, but they cannot give a precise reading of the alcohol concentration and most are use-once-and-toss.
Pernice said his team's proposed device combines the best elements of each of these two breathalyser models.
"Our approach enables an optical, naked-eye detection as a colour change from green to red, like litmus paper," Pernice said in the study published in The Optical Society's (OSA) journal Optical Materials Express.
"But it also potentially permits accurate quantitative measurements" with the addition of an electronic system or a colour detector.
The method is inspired by the natural behaviour of opals, gemstones whose iridescence illustrates their ability to manipulate light.
The researchers created sheets of manufactured opal about one centimetre square and just a few hundred billionths of a meter thick, as thin as some of the films on soap bubbles.
The opals are pumped full of a gel tuned to respond to ethanol vapour. At increasing ethanol concentrations, the gel swells, changing the way light travels through the gel-filled opal and causing the sample to become red.
The change in colour is clearly visible to the naked eye, Pernice said and the device is usable multiple times. After performing the measurements, researchers found that the sample gradually regained its original green colour after less than one minute of exposure in air.