Those beads of sweat trickling down your back during a cardio session, or after savouring some spicy cuisine, aren't just about cooling off. An emerging area of diagnostic research suggests that sweat—which contains electrolytes, metabolites and hormones—hold valuable clues about our health. From metabolic function to nutritional status, sweat can provide similar information that blood tests do, but without painful needle pricks involved.
According to Le Yang, Group Leader at A*STAR’s Institute for Materials Research and Engineering (IMRE), technologies that support health monitoring through non-invasive biochemical analysis can aid both clinical-level diagnostics and personal health tracking, with the potential for smartwatch integration. However, current wearable devices for biofluid analysis often involve complex fabrication processes, high costs, and a lack of user comfort and simplicity.
With collaborators from A*STAR’s Institute of High Performance Computing (IHPC) and Nanyang Technological University, Singapore, Yang, Xinting Zheng, Xiaodi Su and IMRE colleagues set out to develop a new design for biofluid analytical devices. Their solution: a paper patch that can attach to the skin’s surface and absorb sweat, change colours depending on the presence of key biomarkers, and produce unique patterns readable by a smartphone camera.
“When placed on sweaty skin, sweat enters the patch through two holes at the bottom, then flows through the paper’s pores into four detection zones,” said Zheng. “Each detection zone on the patch—which contains a combination of enzymes, nanoparticles and organic dyes—elicits a change in colour intensity, or develops a new colour, which corresponds to biomarker concentrations or overall pH.”
The sensor patch employs a unique ceramic-based ink to control where sweat flows in the patch. Developed by the team, the ink can be printed directly onto a cellulose substrate (i.e., paper) to form sweat-wicking channels akin to COVID or pregnancy test kits.
"Compared to conventional wax-printed patterns, our ink has several advantages: it creates an impervious barrier for sweat, can be printed at a higher resolution, and is more resistant to high temperatures and destructive chemicals,” said Zheng.
The researchers carried out extensive optimisation on their patch prototypes using real and artificial sweat, fluid dynamics simulations, as well as comparisons with commercial benchtop testing kits. These eventually yielded promising results: their sensor patches demonstrated high recovery rates (99.4–103.7 percent) for sweat pH and three sweat metabolites (glucose, lactate and uric acid).
“When we tested the optimised patch on-body with volunteers, we were excited to find it was user-friendly and tallied with readings from commercial kits,” said Yang. “Many commercial sweat analysis technologies need users to exercise to produce enough detectable sweat, but this patch only needs a tiny droplet.”
With groundwork laid for non-invasive, simple and scalable real-time monitoring of sweat biomarkers and sweat rate, the team has filed a patent for their design. “In our upcoming work, our wearable sensors will enable continuous real-time monitoring, and be stable and sensitive enough for reliable long-term use,” said Yang.
The A*STAR-affiliated researchers contributing to this research are from the Institute for Materials Research and Engineering (IMRE) and the Institute of High Performance Computing (IHPC).
