Researchers based at the University of California (UC) San Diego have produced a wearable device that can be wrapped around a finger like a plaster and can measure metabolites in the sweat such as glucose, vitamin C, lactate and levodopa.
Writing in the journal Nature Electronics, the researchers report that not only can the device measure chemicals in the sweat, it is also powered by sweat and therefore has the potential to make continuous measurements over time.
“Wearable sensors can be used to measure different biological signals in real-time. However, the widespread deployment of wearable electronics is restricted by a number of practical limitations including safety and biocompatibility, large device footprint, unreliable operation and inconvenient usage,” explained lead author Joseph Wang, a professor in the Aiiso Yufeng Li Family Department of Chemical and Nano Engineering at UC San Diego, and colleagues.
“The use of rigid batteries in turn increases the device footprint, requires frequent battery charging or replacement, and creates a potential safety hazard. Alternatively, wearable energy harvesters can be integrated, but with the system reliant on energy input from a specific external environment (such as light and temperature) or user activity (such as movement and exercise). This can increase complexity, requiring the addition of conversion and regulation circuits, which cause energy loss.”
The prototype device created by Wang and colleagues is thin and very malleable and has biofuel cells next to the fingertip that are able to convert components of the sweat into electricity, which is then stored in stretchy silver chloride-zinc batteries. These then power four different sensors that can measure four different biomarkers—glucose, vitamin C, lactate and levodopa.
Fingertips have a high number of sweat glands and a fast sweat production, which makes them a suitable place to wear such a device. “It is based on a remarkable integration of energy harvesting and storage components, with multiple biosensors in a fluidic microchannel, along with the corresponding electronic controller, all at the fingertip,” said Wang, in a press statement.
Metabolites are constantly supplied to the sensors by a process of osmosis and an integrated chip allows wireless connectivity so that readings can be transmitted by Bluetooth to either a phone or laptop application.
The researchers tested the device on healthy volunteers after a meal, exercising, consumption of a vitamin C supplement and consumption of fava beans, to measure glucose, lactate, vitamin C and levodopa levels, respectively, and found the sensor was able to detect the expected metabolite changes to a good level of accuracy.
“This is automatic health monitoring at your fingertips,” said study co-first author Shichao Ding, a postdoctoral researcher in Wang’s research group at the UC San Diego Jacobs School of Engineering. “The wearer can be resting or asleep, and the device can still harvest energy and track biomarker levels.”
The technology is still at an early stage of development, but the researchers say that the sensors could be changed to test for different biomarkers if needed. They also think their technology could be used in closed loop systems such as an artificial pancreas for people with type 1 diabetes, which senses glucose and then sends a signal to administer insulin as needed.
