Silk-ionic liquid lactate biosensor with a diffusion layer for wide-range and high-sensitivity sweat analysis

Wearable technologies have emerged as transformative tools in modern societies, enabling non-invasive and continuous monitoring of physiological parameters outside traditional clinical settings. Practical deployment of biosensors into compact wearable systems requires overcoming key challenges, like achieving sufficient signal stability, specificity, miniaturization, portability, and, most critically, long-term operational reliability and manufacturing scalability. Here, we address some of these challenges by presenting a hybrid electrochemical biosensor for lactate detection in human sweat, integrating silk fibroin as a bioactive immobilization matrix, ionic liquids (ILs) as ionic conductivity enhancers, and a Prussian Blue-based transducer. Silk fibroin significantly enhanced lactate oxidase stability and catalytic activity, while the incorporation of ILs improved ionic transport, thereby favoring electron transfer and increasing sensor sensitivity. To overcome the intrinsically narrow linear range of enzymatic lactate sensors, a diffusion-modulating top layer was engineered, enabling controlled mass transport and extending the measurable range to the full physiological lactate window in sweat (0.5-70 mM). The resulting biosensor exhibited high sensitivity, robust linearity, and stable performance. Validation with artificial and real sweat samples demonstrated accurate quantification and >90% recovery, with strong agreement with ion chromatography. The SF/IL architecture provides a versatile scaffold that could be extended to simultaneous multi-analyte detection, enabling comprehensive, real-time metabolic profiling from a single sweat patch, enabling non-invasive, continuous, and personalized health monitoring.