A Granular Hydrogel‐Enabled Wearable Electrochemical Biosensing Platform for Continuous Non‐Invasive Sweat Lactate Detection

Although continuous and non-invasive measurements of sweat biomarkers may provide vital health information, sweat collection often involves intense physical activities or chemical/thermal stimuli. The natural body sweat during endogenous metabolic or stress processes, secreted at much lower rates at rest, may be continuously analyzed using microfluidic devices integrated with hydrophilic rigid fillers; however, the sweat uptake and accumulation in thermoregulatory processes take too long for near-real-time measurements. This work provides an innovative body fluid collection strategy using a granular hydrogel scaffold (GHS), facilitating osmotic and capillary effects to uptake and transfer an ultralow amount of sweat into a microfluidic device at rest. Taken together with a spiral microfluidic channel, the GHS-embedded microfluidics reduce the evaporation of collected sweat and store it in a sensing well for near-real-time measurements. Integrating the sweat-collecting system with an enzymatic gold-graphene nanocomposite-modified laser-induced graphene (LIG) electrode and a LIG-based pH sensor enables the accurate continuous on-body detection of sweat lactate during normal daily activities at a low perspiration rate. The novel combination of a GHS-integrated microfluidic system with a low-cost, flexible, sensitive, and stable LIG-based sensing system provides an accessible technology for sweat-based biosensing during normal daily activities.