Joe Wang, distinguished professor in UCSD's Department of Nanoengineering and faculty director of its wearables center, showcased temporary tattoos outfitted with electrochemical sensors to monitor electrolytes and metabolites in real-time. The tattoos are screen printed and can be worn for up to a week.

Screen printed tattoos would need to be worn with an additional device that would send data via Bluetooth LE. (Image: UCSD)

"The skin is an important sensory function," Wang said at TSensors Summit . "The skin is not only our own body, but it could be the body of any host like a building, a tree, or a moving car."

Such sensing devices "couple favorable substrate-skin elasticity along with an attractive electrochemical performance" for highly efficient sensing. Attached sensors did non-invasive diabetes monitoring using tears and were also able to assess endurance and performance through sweat. The tattoos were able to withstand at least 50 manipulations and still retain shape and performance.

The sensors allow for measurement of trace heavy metal elements such as lead down to a parts-per-billion level. Wang added that the tattoo sensors could also be used to harvest energy in the form of a printable biofuel or zinc battery, which could potentially power an LED with sweat.

Several Center for Wearable Sensors research projects. (Image: UCSD)

Research began with printable textile-based sensors sewn into the elastic waist of underwear to measure performance. Multi-electrode layers on garments were eventually able to sense explosives while a "forensic finger" on a glove could do an on-spot analysis of a crime scene.

"The goal was to develop a forensic lab on a sleeve with detection of explosives and gunshot residue all integrated with supporting electronics on a sleeve, on a textile," Wang said.

Wang and team also worked with the Navy to put printable sensors on a wetsuit to monitor underwater security and environmental conditions. Other prototypes monitored saliva in a mouth guard.

Minimally invasive micro