Scalable e-textiles with bio-inspired sea-island electrostatic heterostructures for ion-selective sweat sensing

Achieving large-scale, ion-selective sensing remains a critical challenge in the development of wearable health-monitoring systems with clinical relevance. Here, we present a bio-inspired sea-island electrostatic heterostructure that enhances ion selectivity by engineering a spatially patterned charge interface, in which graphene (Gr) serves as a negatively charged sea and polylysine modified Fe 3 O 4 (PLL@Fe 3 O 4 ) nanoparticles act as positively charged islands. This heterostructure generates local electrostatic gradients that preferentially facilitate K + over Na + transport based on differences in hydration shell deformability. To enable scalable fabrication, we developed a shear-thinning PLL@Fe 3 O 4 /Gr ink suitable for screen printing, allowing the creation of flexible e-textile sensor arrays. The Na + /K + selectivity coefficient improved significantly from ~0.95 (Gr) to ~1.45 (PLL@Fe 3 O 4 /Gr), representing an enhancement of approximately 53 %. The printed sensors exhibited excellent stability during continuous sweat monitoring and successfully generated early warning signals under simulated hypokalemia conditions. This work provides a scalable and effective strategy for constructing high-performance, ion-selective textile biosensors, bridging fundamental ion transport principles with real-world applications in wearable healthcare platforms.