The small device, approximately five centimetres square, can be placed directly on the skin and worn 24/7 for around-the-clock health monitoring.
It is the brain child of Northwestern University and University of Illinois at Urbana-Champaign, and the wireless technology uses thousands of tiny liquid crystals on a flexible substrate to sense heat. When the device turns colour, the wearer knows something is wrong.
"Our device is mechanically invisible -- it is ultrathin and comfortable -- much like skin itself," says Northwestern's Yonggang Huang, one of the senior researchers.
"One can imagine cosmetics companies being interested in the ability to measure skin's dryness in a portable and non-intrusive way. This is the first device of its kind."
Practical
The device stretches and compresses with the skin as it moves, and uses the transient temperature change at the skin's surface to determine blood flow rate, which is of direct relevance to cardiovascular health, and skin hydration levels.
It comprises up to 3,600 liquid crystals, each half a millimetre square, laid out on a thin, soft and stretchable substrate. When a crystal senses temperature, it changes colour and the dense array provides a snapshot of how the temperature is distributed across the area of the device.
An algorithm translates the temperature data into an accurate health report, all in less than 30 seconds.
"These results provide the first examples of 'epidermal' photonic sensors," adds John A. Rogers, the paper's corresponding author and a Swanlund Chair and professor of materials science and engineering at the University of Illinois.
"This technology significantly expands the range of functionality in skin-mounted devices beyond that possible with electronics alone."
Technology
The photonic device has 3,600 temperature points, providing sub-millimetre spatial resolution that is comparable to the infrared technology currently used in hospitals.
The infrared technology, however, is expensive and limited to clinical and laboratory settings, while the new device offers low cost and portability.
The device also has a wireless heating system that can be powered by electromagnetic waves present in the air. The heating system is used to determine the thermal properties of the skin.
Li Gao, Yihui Zhang, Viktor Malyarchuk, Lin Jia, Kyung-In Jang, R Chad Webb, Haoran Fu, Yan Shi, Guoyan Zhou, Luke Shi, Deesha Shah, Xian Huang, Baoxing Xu, Cunjiang Yu, Yonggang Huang, John A. Rogers. Epidermal photonic devices for quantitative imaging of temperature and thermal transport characteristics of the skin. Nature Communications, 2014; 5: 4938 DOI: 10.1038/ncomms5938