Paper-based wearable array sensor for simultaneous real-time monitoring of lactate and pH in human sweat

Wearable electrochemical sensors have attracted considerable attention as promising tools for non-invasive analysis of biomarkers in human sweat. In this study, a paper-based potentiometric sensor array was fabricated for simultaneous real-time monitoring of lactate ion and pH in human sweat. The lactate sensor was based on a lactate-doped conductive polypyrrole (PPy), while the pH sensor was based on sulfanilic acid-doped PPy. Both sensors were electrochemically synthesized on conductive paper, resulting in a flexible sensing platform for wearable applications. The lactate and pH sensors exhibited Nernstian sensitivities of -58.52 mV decade^-1 and -49.57 mV pH^-1, respectively. The lactate sensor showed a linear response over the concentration range of 1 × 10^-7 to 1 × 10^-2 mol L^-1, while the pH sensor showed a linear response over the pH range of 2-8. The sensors responded rapidly with a response time of ≤ 1 s and showed good repeatability and stability during measurements. Selectivity was evaluated in the presence of common sweat constituents, including sodium, potassium, calcium, copper(II), ammonium, glucose, ascorbic acid, urea, and chloride ions, showing negligible interference. To evaluate its practical applicability, the sensor array was integrated into a fabric headband and tested for real-time sweat monitoring during physical activity. The results demonstrated stable and real-time monitoring performance, confirming the suitability of the proposed setup for sweat analysis. The combination of paper-based substrate, straightforward fabrication, and reliable sensing performance makes this platform a promising candidate for next-generation wearable health-monitoring devices.