Successful wearable sweat sensors require consistent sweat collection and stable electrical sensing interfaces. Sweat secretion varies widely depending on physical activity and environmental conditions, making continuous sweat sampling difficult, particularly in sedentary scenarios. Earlier approaches, such as patch-type microfluidic systems and active sweat induction via Joule heating or iontophoresis, improve sampling but typically require complex external power sources and circuitry.
An ideal sweat sensor thus must collect sweat passively, maintain conformal, comfortable contact with skin, and operate reliably without auxiliary devices. MoS2, a two-dimensional semiconducting nanomaterial, offers unique electrical and chemical properties ideal for sensing ions and metabolites. Incorporating MoS2 into flexible composite fibers with PLA can combine the sensing functionality with wearable comfort and passive fluid transport.
Structural and Chemical Characterization of Functional Fibers
MoS2 nanosheets were prepared by electrochemical exfoliation of bulk crystals, yielding high-quality two-dimensional flakes that retain the semiconducting 2H phase, with minor metallic 1T contributions to enhance charge transport. The nanosheets were dispersed and mixed with biodegradable PLA polymer dissolved in a heated solvent to create a precursor spinning dope.
Wet spinning using a customized slit nozzle extruded this mixture into continuous composite fibers, which were coagulated and dried. The resulting fibers exhibited a porous microstructure advantageous for sweat interface sensing and fluid uptake.
The fibers’ composition and structure were characterized through scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy, confirming the uniform distribution of MoS2 and PLA and the preservation of semiconducting phases critical for sensor operation. Electrochemical and electrical measurements were performed to evaluate the fibers’ response to biologically relevant ions and metabolites. Importantly, the inherent capillary action within the porous structure was leveraged to collect microvolume sweat passively without external power.
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Thermal Microenvironment Stabilization and Sweat Collection Dynamics
The MoS2/PLA composite fibers maintained a thermally insulated microenvironment when worn on the skin, stabilizing sweat secretion conditions by minimizing heat loss and evaporation. The porous fiber morphology facilitated rapid capillary uptake of sweat droplets even in microvolume amounts as low as 0.5 µL, demonstrating sensitive real-time transduction of sweat composition changes.
Electrochemical tests showed that the sensor selectively detected key biomarkers: sodium and potassium ions influenced sensor conductivity via electrostatic screening, increasing conductivity, while metabolites like lactic acid and ammonium induced charge trapping and scattering, reducing conductivity. These distinct mechanisms enabled the sensor to differentiate among multiple sweat analytes effectively.
Tests on human subjects under various physiological conditions, exercise, heat stress, and psychological stress, revealed unique temporal sweat profiles captured by the fiber sensors. Differences in sweat onset time, peak intensities, and decay curves were clearly distinguished, underscoring the sensor's ability to track diverse physiological states in real life, even with low perspiration rates and signal fluctuations.
Besides biochemical sensing, the fiber’s piezoresistive nature enabled detection of mechanical pressure through changes in electrical resistance. Compression densified the MoS2 network, lowering resistance and providing a clear, reversible signal proportional to applied pressure from 1 to 5 N, within force levels common in daily wear. Mechanical durability tests confirmed negligible performance degradation after 500 bending cycles with tight curvature, affirming robustness for wearable applications.
This dual-sensing functionality permits concurrent monitoring of biochemical sweat parameters and physical activity or movement, expanding the sensor’s utility for comprehensive health tracking. Collectively, these results demonstrate that the MoS2/PLA composite fiber sensor platform meets critical demands for wearable sweat sensors by ensuring continuous, power-free sweat sampling, selective biomarker detection, mechanical compliance, and multifunctionality in a textile-integrated form factor.
Implications for Next-Generation Wearable Bioelectronic Systems
This study presents a robust, multifunctional sweat sensor platform based on semiconducting MoS2/PLA composite fibers produced via wet spinning, which integrates seamlessly into wearable textiles. The fibers’ intrinsic thermal insulation and capillary properties enable passive, efficient sweat collection even under low perspiration without an external power supply. Exploiting the material’s n-type semiconducting characteristics and electrochemical interaction mechanisms, the platform selectively detects important sweat biomarkers, including electrolytes and metabolites, distinguishing their effects on conductivity.
Additionally, its piezoresistive response facilitates simultaneous sensing of mechanical pressures related to physical movement, offering expanded physiological monitoring capabilities. The fiber sensors exhibit strong mechanical durability and flexibility required for long-term, noninvasive skin contact. This textile-compatible, multifunctional sensing approach paves the way for next-generation wearable technologies in healthcare diagnostics, sports science, and personalized monitoring, promising broad impact across biomedical engineering and wearable electronics industries.
Journal Reference
Park J. H., Park J. W., et al. (2026). Multifunctional Sweat Sensors Using Semiconductor Fibers Based on Two-Dimensional Nanomaterials. Small Structures, 7, e202500905. DOI: 10.1002/sstr.202500905, https://onlinelibrary.wiley.com/doi/10.1002/sstr.202500905