Lyocell–modal thread microfluidic platform integrated with a microneedle sensor for lactate detection in saliva

The advancement of wearable and point-of-care (POC) biosensing technologies has driven a growing demand for microfluidic substrates that are flexible, hydrophilic, and compatible with electrochemical sensing. In this study, a lyocell-based thread microfluidic platform was developed to overcome limitations of conventional microfluidic systems. The device employs polypropylene (PP) mesh as a structural substrate and is coupled with a modal absorption pad to sustain consistent and continuous liquid transport. Lyocell's inherent capillary-driven wicking, superior hydrophilicity, semicrystalline microstructure, and high wet modulus collectively provide excellent liquid transport efficiency, structural stability under wet conditions, and bubble-free flow. Experimental analysis revealed that unmodified lyocell achieved liquid transport velocities comparable to plasma-treated cotton, confirming its intrinsic capillary efficiency. When integrated with a microneedle-based electrochemical sensor, the device demonstrated rapid analyte delivery and stable signal generation for both ferrocyanide and lactate detection. The thread-integrated lactate sensor exhibited a strong log-linear correlation, with limits of detection (LoD) of 0.433 mM using chronoamperometry (CA) and 0.51 mM using differential pulse voltammetry (DPV). Human saliva testing was also conducted using saliva samples, and the results were compared with blood lactate concentrations. A strong correlation was observed between salivary and blood lactate levels (R = 0.94). Overall, the lyocell-modal hybrid microfluidic platform provides a sustainable, low-cost, and scalable strategy for electrochemical point-of-care testing (POCT), offering a promising route toward next-generation lab-on-fabric systems.