Ultrathin and Anti-friction Janus Bioelectrodes for Imperceptible Electrochemical Sweat Analysis

Skin-like electrochemical sweat biosensors hold great promise for non-invasive and unobtrusive health monitoring, yet their real-world application is severely hindered by poor durability under repeated skin friction, stretching, and sweat erosion. Here, we report a versatile Janus bioelectrode design that simultaneously achieves ultralow thickness, high stretchability, and exceptional anti-friction performance for reliable sweat sensing. The Janus architecture prepared by sequential screen printing and thermal annealing, provides strong interfacial adhesion with strain-insensitive conductivity. The resulting ultrathin electrodes (∼20 µm) survive over 1600 s of Radio Corporation of America (RCA) abrasion and 500% tensile strain without significant degradation in conductivity or electrochemical stability. We further functionalized the Janus bioelectrodes into a durable three-electrode system for uric acid (UA) sensing. As a proof of concept, we attached the tattoo-like sensor onto a human forearm to enable real-time, wireless monitoring of sweat UA during both aerobic and anaerobic exercise. The sensor printed directly onto a T-shirt survived prolonged use and daily laundry cycles. This work establishes a general strategy for creating ultrathin, durable electrochemical biosensors that resist motion artifacts and friction, paving the way for robust and imperceptible electrochemical sweat analysis.