A reusable, wireless, battery-free, noninvasive sweat cortisol sensor

The realm of wearable sensors has seen remarkable growth, driven by advancements in continuous, real-time tracking of physiological and molecular biomarkers for health monitoring. Yet, their wider adoption is hindered by challenges such as the need for advanced materials that are biocompatible, flexible, and mechanically durable, alongside traditional fabrication methods that are often costly and time-consuming. Herein, we developed an innovative approach utilizing 3Dnanomaterials printing, which offers low-cost, rapid prototyping, scalability, and high resolution to fabricate tunable nanomaterials tailored for wearable sensing applications. This allowed us to create ultrathin (30 μm) nanomaterials that closely mimic human skin's mechanical properties and can endure up to 400% stretching and 30° bending without damage. As proof of concept, we successfully developed a flexible wearable sensor that is portable, comfortable to wear for noninvasive cortisol sensing in-situ. Furthermore, the sensor integrates a battery-free flexible readout circuit custom designed to be operable using a smartphone for on-demand real-time cortisol tracking. This innovative method presents a costeffective, simple, highly reliable, and practical solution for advanced health monitoring.