High-strength, high-toughness regenerated cellulose/graphene oxide nanofluidic membrane with highly oriented and charged nanochannels for wearable sweat-monitoring systems

Nanofluids with directional, selective, and efficient ion-transport properties are widely used in energy-conversion research. However, designing wearable nanofluidic systems for personal health monitoring is challenging owing to the large size of the test equipment, complex preparation process, and stringent biosafety requirements. Herein, we present a bottom-up strategy, integrating structural orientation, densification, and charge, to prepare a robust regenerated cellulose/graphene oxide nanofluidic membrane (TACM) comprising well-aligned nanochannels (3–4 nm) and negatively charged surfaces. The TACM exhibited high strength (76.27 MPa) and toughness (24.56 MJ m−3) as well as excellent ionic conductivity (0.65 S m−1) at low salt concentrations (<0.001 mM), attributed to the selective transport properties of the ordered charged nanochannels for oppositely charged ions, as demonstrated by experiments and finite-element simulations. In addition, we fabricated a sweat-sensing system incorporating the TACM as a core, which successfully monitored sweat changes during various aerobic and anaerobic exercises and provided health alerts. This study contributes toward the application of biomass-based nanofluids in health monitoring and alerting systems.