Researchers have developed a variety of wearable and non-invasive sensors in recent years. Some examples include: an electronic-skin coating that can detect blood oxygen levels; contact lenses made from metal-oxide thin films that can detect glucose levels in tears; and flexible integrated sensor arrays based on plastic and silicon integrated circuits that can detect molecules like glucose in sweat.

Now, a team led by Patrick Mercier and Joseph Wang have developed a tattoo-like patch containing flexible, wireless electronics that measures ethanol in sweat in three stages. First, the device induces sweating by delivering a small amount of the drug pilocarpine across the wearer’s skin. Next, an alcohol-oxidase enzyme reaction and a Prussian blue electrode transducer allow the amount of alcohol present in the sweat to be determined (see figure). Finally, a flexible electronic circuit board transmits the data via Bluetooth to a mobile device or laptop.

The three steps combined take less than eight minutes.

Can I drive right now?

"Non-invasive blood alcohol monitoring in real time is a big challenge," says Mercier. "Breathalysers do not directly measure blood alcohol (but calculate it indirectly by following Henry’s Law) and measurements made by existing commercial devices take several hours to produce results (rendering questions like ‘can I drive right now’ difficult to answer).

"In our device, we were able to show that by inducing sweating through an iontophoretic process, we can estimate blood alcohol concentrations in a matter of minutes rather than hours. What is more, we were able to develop the technology in a thin, conformal system that wirelessly sends information to a smartphone or watch, thereby making it much less bulky than existing products."

Promising alternative to breathalysers

The new device might be a promising alternative to breathalysers, which can sometimes produce "false positives" (for example, if a person has recently used mouthwash or a breath freshener, or if there are paint or varnish fumes in their surrounding environment).

The device might also be adapted so that it can be connected to a vehicle’s ignition interlock system. Someone whose blood alcohol concentration was above the legal limit would not then be able to start his or her car. It might also be a useful tool for bartenders and friends, quip the researchers.

Device might even be able to detect dopants

So when could we see such a device being commercialized? Mercier says that it is difficult to predict at this point since there are still several challenges that need to be addressed. "For example, how long could it be worn by a person before it became damaged? How robust is it to daily wear and tear? I would expect a few years from now might be reasonable estimate though," he tells nanotechweb.org.

Guihua Yu of the University of Texas at Austin, who says that this is a "nice piece of work and a novel design for flexible "all-integrated" alcohol sensors mountable on skin for accurate yet efficient detection of ethanol content. Compared to other recent works on skin/wearable sensors, Mercier and Wang have gone a step further by integrating a sweat inducer, printed electrodes and Bluetooth transmitter all together in a wearable tattoo platform." The UCSD team, reporting its work in ACS Sensors DOI: 10.1021/acssensors.6b00356, is now busy further miniaturizing its device and improving its robustness. In the future, it might even be able to detect other analytes – for instance, the presence of dopants in athletes’ sweat.