A wax-printed Janus paper-based microfluidic wearable sensor for metabolic analysis in sweat

Wearable sweat sensors enable noninvasive, real-time biochemical monitoring, holding significant potential for personalized healthcare. Recently, microfluidic paper-based devices have gained attention in this field for their facile fabrication, cost-effectiveness, and self-actuating operation without equipment. However, the limited liquid-holding capacity of paper restricts sustained directional transport upon saturation, impeding long-term on-body monitoring. Here, we demonstrate a wireless wearable system based on Janus paper-based microfluidic patch (JPMP) for non-invasion real-time continuous detection of three typical metabolic analytes: glucose, creatinine, and uric acid in sweat. JPMP integrates a pair of wax-printed Janus papers in the sweat collection and drainage layers, inspired by the asymmetric wettability of lotus leaves and the tip-directed liquid transport of leaf-tips, to achieve continuous and efficient unidirectional sweat transport, even under saturation conditions. The wax printing method offers a facile and controllable strategy for the scalable fabrication of patterned Janus paper. For multi-parameter detection, JPMP incorporates a paper-based sensor array featuring working electrodes prepared by D-sorbitol-doped PEDOT: PSS conductive ink, fully utilizing porous structure of paper to achieve highly sensitive electrochemical detection. Furthermore, we proposed a method for in-situ growth of three-enzyme-inorganic hybrid nanoflowers on the electrode, successfully extending the lifespan of creatinine enzymatic electrodes. Finally, we evaluated the postprandial metabolic status of healthy participants to validate the wearable system for continuous real-time on-body monitoring, demonstrating its potential for personalized metabolic healthcare.