Electronic skin sensor detects heatstroke danger

(Nanowerk Spotlight) Heat strokes – a severe heat-related illness that occurs when the body can't cope with heat anymore – are medical emergencies that will become a growing problem as the occurrence of extreme heat waves increases around the globe. When therapy is delayed, the mortality rate may be as high as 80%; however, with early diagnosis and immediate cooling, the mortality rate can be reduced to 10%. Mortality is highest among the elderly population, patients with preexisting disease, those confined to a bed, and those who are socially isolated.
A simple solution for this problem is to make sure the body is sufficiently hydrated. However, people may not know that they lack in hydration. In these cases, during hot temperatures, the water level in the body can decrease to a level where sweating stops. The body temperature then quickly rises over 40 °C, ultimately leading to a heatstroke.
A research team in Japan, lead by Prof.Kazuyoshi Tsuchiya, now has developed a tattoo-like sensor system that sticks to the skin and can indirectly tell the body's hydration level.
Reporting their findings in ACS Sensors ("Advanced Artificial Electronic Skin Based pH Sensing System for Heatstroke Detection"), a team from Tokai University demonstrated a completely new, versatile strategy to integrate pH sensing elements with high quality, physically transferable PDMS freestanding nanosheets.
"The secret behind this sensor integration onto a nanosheet is that we discovered that Ag/AgIO3 (silver iodate) can work as reference electrode without any electrolyte solution," Dr. Ganesh Kumar Mani, a JSPS Post-Doctoral Fellow in the Micro/Nano Technology Center at Tokai University, tells Nanowerk. "Ag/AgCl is the most used reference electrode for potentiometric studies, however it is bulky and always contains KCl electrolyte solution. For a miniaturized system, we wanted to get rid of the electrolyte solution and we discovered Ag/AgIO3 as the solution."
The researchers prepared their ultra flexible, freestanding nanosheets (∼ 100nm thick) combined with pH sensing elements by spin coating and sputtering techniques These sensor stickers can adhere to the skin – or even internal organs – without any glue.
e-skin pH sensor fabrication procedure
(a) Schematic of the e-skin pH sensor fabrication procedure; (b) photograph of the pristine PDMS nanosheet; (c) freestanding pH sensor nanosheet on clean wipes, and (d) pH sensing nanosheet sensors transferred on artificial arm. (Reprinted with permission by American Chemical Society) (click on image to enlarge)
"We tested the nanosheet pH sensing response with various pH solutions and achieved a sensitivity of 43 mV/pH," Ganesh points out. "The simple structure of our sensor combined with a thin film pH sensor offers a unique advantage in testing in situ heatstroke detection."
He notes that it is also possible to functionalize the freestanding nanosheets with other materials that could open vast opportunities in biomedical fields.
The next stages of the team's investigation are to test with longer testing times, sensitivity analysis with real sweat from humans, and integration with a WiFi module. With the help of Tokai University Medical School they also hope to be able to soon start clinical testing.
"To the best of our knowledge, this is the first report on the preparation of such a structure for in situ pH monitoring," he concludes. "Investigation on detailed animal studies and improving the adhesion for long-term usage are now in progress."
Michael Berger By – Michael is author of three books by the Royal Society of Chemistry:
Nano-Society: Pushing the Boundaries of Technology,
Nanotechnology: The Future is Tiny, and
Nanoengineering: The Skills and Tools Making Technology Invisible
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