Flexible electronics track sweat

Fitness trackers just got an upgrade.

A new electronic health-monitoring device can sense a person’s temperature and analyze chemicals in a drop of sweat. It sends those data wirelessly to a smartphone app. And it all fits in a package about the size of a few postage stamps.

The gadget could help athletes instantly tell whether they’re getting enough fluids, or hydration. Or it could give scientists an easy way to collect data for medical studies — with no poking or prodding.

Researchers have built sweat sensors before. But the new device “represents a whole ‘nother level of sophistication,” says materials scientist John Rogers. He works for the University of Illinois at Urbana-Champaign. He also was not involved in this study.

Previous sensors have detected only a single chemical. The new sensor can measure four that are present in sweat, all at once. Ali Javey and his colleagues described their findings January 27 in Nature.

Traditional electronics rely on “brains” made of tiny circuits laid out on silicon chips. “But the problem with silicon chips is that they’re way too small and rigid,” says Javey. He’s an electrical engineer at University of California, Berkeley. Silicon chips are great for data processing — not for making sensors that hug the skin. For that, rubbery electronics that can twist and flex are ideal. But they don’t have the processing power of silicon-based versions.

So scientists typically use flexible electronics for sensing. Then they turn to traditional electronics to do the “thinking.” Later, they link the two with long wires. Javey’s team merged these two technologies into a single, wireless device. “This level of integration is amazing,” says Dae-Hyeong Kim. He’s a bioengineer at Seoul National University in South Korea.

The researchers tested their sweat-sensing device on volunteers in and out of the lab. In one test, 12 volunteers wore the device tucked into a headband while running outdoors. Six runners drank water every five minutes. The other six drank nothing. After about an hour and a half, the sweat sensor picked up an increase in sodium levels in people who had drunk nothing. That’s a sign of dehydration — that they were losing too much water.

Javey says tweaking the device could make it useful beyond athletics. Researchers could one day use it to diagnose lead poisoning in children without blood tests. Or perhaps they could even use it to detect molecules in sweat that are linked to depression. 

Power Words

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bioengineering The application of technology for the beneficial manipulation of living things. Researchers in this field use the principles of biology and the techniques of engineering to design organisms or products that can mimic, replace or augment the chemical or physical processes present in existing organisms. This field includes researchers who genetically modify organisms, including microbes. It also includes researchers who design medical devices such as artificial hearts and artificial limbs. Someone who works in this field is known as a bioengineer.

circuit  A network of that transmits electrical signals. In the body, nerve cells create circuits that relay electrical signals to the brain. In electronics, wires typically route those signals to activate some mechanical, computational or other function.

computer chip (also integrated circuit)  The computer component that processes and stores information.

data processing  Putting information into a computer and having the computer store, organize or change it.

dehydrate To lose a large amount of water.

depression A mental illness characterized by persistent sadness and apathy. Although these feelings can be triggered by events, such as the death of a loved one or the move to a new city, that isn’t typically considered an “illness” — unless the symptoms are prolonged and harm an individual’s ability to perform normal daily tasks (such as working, sleeping or interacting with others). People suffering from depression often feel they lack the energy needed to get anything done. They may have difficulty concentrating on things or showing an interest in normal events. Many times, these feelings seem to be triggered by nothing; they can appear out of nowhere.

electrical engineer  An engineer who designs, builds or analyzes electrical equipment.

electronics  Devices that are powered by electricity but whose properties are controlled by the semiconductors or other circuitry that channel or gate the movement of electric charges.

glucose   A simple sugar that is an important energy source in living organisms. It is half of the molecule that makes up table sugar (also known as sucrose).

hydrate (noun: hydration) To restore the proper level of fluids in the body.

lead     A toxic heavy metal (abbreviated as Pb) that in the body moves to where calcium wants to go. The metal is particularly toxic to the brain, where in a child’s developing brain it can permanently impair IQ, even at relatively low levels.

materials science  The study of how the atomic and molecular structure of a material is related to its overall properties. Materials scientists can design new materials or analyze existing ones. Their analyses of a material’s overall properties (such as density, strength and melting point) can help engineers and other researchers select materials that are best suited to a new application.

molecule An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O₂), but water is made of two hydrogen atoms and one oxygen atom (H₂O).

potassium  A chemical element that occurs as a soft, silver-colored metal. Highly reactive, it burns on contact with air or water with a violet flame. It is found in ocean water, as part of sea salt, and is also found in many minerals.

sensor  A device that picks up information on physical or chemical conditions — such as temperature, barometric pressure, salinity, humidity, pH, light intensity or radiation — and stores or broadcasts that information. Scientists and engineers often rely on sensors to inform them of conditions that may change over time or that exist far from where a researcher can measure them directly.

silicon   A nonmetal, semiconducting element used in making electronic circuits. Pure silicon exists in a shiny, dark-gray crystalline form and as a shapeless powder.

smartphone A cell (or mobile) phone that can perform a host of functions, including search for information on the Internet.

sodium A soft, silvery metallic element that will interact explosively when added to water. It is also a basic building block of table salt (a molecule of which consists of one atom of sodium and one atom of chlorine: NaCl).