Breathalyzer removes doubt from roadside readings

Unlike current colour change-based devices, this sensor would be reusable and could also provide a precise digital readout.

The new design is the said to be the first that uses the sensing properties of opal to detect ethanol, the intoxicating component of commercial liquor, by inducing a change in colour that is visible to the human eye. The research team describes their new method in a proof-of-concept paper published today in Optical Materials Express.

The portable breathalyzers used by roadside police use expensive electronic readouts, but these devices lack the ‘immediate and intuitive’ colour change that tells police whether the alcohol content of a suspect’s breath puts them in the legal red zone, said first author Riccardo Pernice of the Università 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 used once before being disposed of. Pernice said his team’s proposed device combines the best elements of each of these two breathalyzer models.

‘Our approach enables an optical, naked-eye detection as a colour change from green to red, like litmus paper,’ Pernice said in a statement. ‘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. Scientists use manufactured versions of opals and other photonic crystals to detect acidity or the presence of liquid ethanol, but until now little attention has been paid by researchers to detecting gaseous ethanol, the researchers said.

In their new setup, the researchers created sheets of manufactured opal about one centimetre square and just a few hundred billionths of a meter thick.

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.

After performing the measurements, the researchers found that the sample gradually regained its original green colour after less than one minute of exposure in air. The sensor does not pose environmental concerns for disposal after use, since it is made of all non-toxic materials, and it does not react to acetone, one of the many substances that can be falsely identified as ethanol by some breath machines.

The device is currently able to detect alcohol at much higher concentrations compared to other portable alcohol sensors. In the coming months, the researchers hope to explore the device’s use at lower concentrations as well.