An international team of scientists has developed a membrane that can sense the presence of sweat when applied to the skin, and is reported to be hundreds of times more effective than conventional methods.
The report, ‘Membrane isolation of repeated-use sweat stimulants for mitigating both direct dermal contact and sweat dilution’, published in the journal Biomicrofluids, identifies the key limitations of similar sweat-sensing devices, which typically employ a sweat stimulant that is dissolved into a hydrogen gel. While effective in activating sweat production, this gel makes it difficult for biosensors to accurately read the sweat, and stimulants cannot be used to target specific areas of the body.
“Everyday use of sweat biosensing is on the horizon, but first we need to work out a few problems, including how to obtain useful samples when patients aren’t exerting themselves,” said Phillip Simmers, one of the authors of the paper. “One of the biggest challenges was that when we sweat, we’re actively losing analytes to the gel, which is an issue that hasn’t been addressed.”
Simmers and his team created an in vitro model to assess the most effective filtration membranes for limiting the diffusion of carbachol, a frequently used sweat stimulant. They found that the best membranes had nanoscale pores and retained more than 90% of their stimulant concentration, while allowing a minimal amount of sweat to pass through.
These membranes were then applied to dime-sized adhesive patches and tested on patients. Using blue bromophenol dye and silicone oil, which changes colour in the presence of sweat, the team demonstrated how the nanoscale pores retained their characteristics when applied to human patients, and that the membrane was effectively separating the sweat from the stimulant.
Wearable sweat sensors have demonstrated medical uses, as sweat can be used to diagnose cystic fibrosis, according to one STANFORD study, or monitor thermal comfort, according to a report by the Korea Advanced Institute of Science and Technology. Simmers and his group plan to incorporate their membrane into a wearable biosensing prototype that they have already developed, and hope that their research will encourage others to investigate how to produce membranes for similar purposes more effectively.