Seeing Through the Skin

by AURAMETRIX

​Human skin emits light (albeit the glow is extremely weak) and a wide variety of small molecules that may be sometimes "sniffed" by dogs or even other humans. These chemicals tell a story about our health and wellness, things we eat and drink, touch and breathe. Mosquitoes use such emissions to assess our "attractiveness" from indicators such as Indoles (unpleasantly smelling but healthy "inner soil" biomarker) or carbon dioxide (amount of which correlates with the size of the person producing it) in the air.  Sampling air for health indicators is much less invasive than drawing blood and could be an invaluable diagnostic tool. Many applications of gas sensors have been proposed over decades ranging from sweat patches to sensorized garments. Where are we now? What is the 2016 state of the art? Last month, BACtrack won 1st Prize in “Wearable Alcohol Sensor Challenge” Issued by National Institutes of Health. Milo Sensors, employing a different approach to identify ethanol molecules diffusing through the skin, won 2nd prize. BACtrack Skyn will be available in limited quantities later this year, marking an important step from bulky alcohol-monitoring ankle bracelets remotely monitoring offenders to inconspicuous devices. Perhaps, one day, drug patches, too, won't require sending them to a lab for analysis. Human skin is a super-highway of many small molecules reflecting our health and wellbeing. Various devices capable of "seeing" through our skin were announced in the past several years. Some of them - like AIRO watch claiming to detect metabolites in your bloodstream as they are released during and after meals - turned out to be vaporware. The jury is still out on many others like HealbeGobe. And the remaining ones are still in prototyping stages.  EU-funded Biotex textiles and Perspiration Detective patch development at the University of Cincinnati started from detecting sodium ions in sweat as indicators of hydration levels. A tattoo-like electronic sweat sensor built by a team in UCSD demonstrated that measuring a change in lactate might be sufficient to find when an athlete is about to “hit the wall.” Startup Electrozyme, later renamed to Biolinq, was formed to commercialize this technology. The picture shows their prototype of a skin-applied electrochemical sensor that analyses body fluids to provide actionable health information. The goal is to develop temporary tattoo biosensors providing blood level info without accessing blood. Halo Wearables will launch their non-invasive hydration monitoring wearable in early 2016. It is tailored specifically for elite athletes.  Halo's optical sensors track sodium and potassium levels in the user's blood. ​ Researchers from the University of California, Berkeley, Stanford and Lawrence Berkeley National Laboratory have also developed a wearable sensor that can monitor sodium, potassium and lactate levels in sweat. A paper with their findings was published in Nature earlier this year. ​ Startup Xsensio, accepted this year in Mass Challenge accelerator, works on “intelligent stamps” the size of a credit card (Lab-on-Skin wearables) including a unique low-power sensor for sweat analysis. ECHO smart patch from Kenzen aims to "silently follow your health and notify you only when it's most important". It analyzes sodium and potassium in sweat to monitor hydration, lactic acid and glucose analysis energy expenditure.  Existing technologies can detect a general increase or decrease in metabolites rather exact concentrations. So using sweat to accurately monitor clinically important variables such as glucose levels, is still out of reach. But developers are employing innovative approaches to make it possible. A team from Seoul National University, University of Texas and a Massachusetts-based company MC10 are developing a flexible patch that senses glucose in people with diabetes and administers drugs, all in a single device. And there may be easier ways to display all the information collected from various sensors -  perhaps even directly on the body - as the team from the University of Tokyo demonstrated with device measuring oxygen saturation levels in blood. ​We've come a long way from bulky and invasive medical equipment that required the patient to remain in the hospital for monitoring. We have made a lot of progress from the times when all symptoms and signs were recorded with a pencil and paper. There is still a lot more to do before real-time self-managing noninvasive diagnostics reaches a breakthrough, but we are so much closer.

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