On-body electrochemical measurement of sweat lactate with the use of paper-based fluidics and 3D-printed flexible wearable biosensor

: Real-time monitoring of sweat lactate provides valuable physiological insights for assessing exercise outcomes and athletic performance. Conventional lactate detection methods, while sensitive, often lack portability and real-time capability for use in wearable or in-body applications. To address these limitations, electrochemical biosensing has emerged as a leading approach, enabling non-invasive and real-time analysis. Wearable devices which integrate lactate-specific enzymes with electrochemical transducers might provide efficient solutions for continuous monitoring. In this study, a wearable lactate biosensor was developed using custom screen-printed electrodes modified with a bio-hybrid probe comprising Prussian blue, carbon black, and lactate oxidase. All the key experimental parameters were optimized, and a detection limit of 60 µM and a linearity up to 20 mM were obtained. A filter paper-based strip was incorporated to enhance sweat collection and serve as the real sample collector by exploiting its porosity: this configuration allowed a satisfactory repeatability of 6%. The system was validated using real sweat samples, highlighting a quantitative correlation (94-103%) with LC-MS/MS measurements. The biosensor was integrated onto a 3D-printed thermoplastic polyurethane (TPU) armband, designed for a customizable and comfortable fit, ensuring effective sweat collection and transport. This low-cost, wearable system represents a significant step forward in non-invasive, continuous, and personalized health monitoring, providing a practical tool for tracking physiological parameters in real-time.