Hierarchical Graphene Nanowall Nanomesh Enables Confinement-Enhanced Gas Sensing for Wearable Applications

Wearable gas sensors are essential for real-time monitoring of personal exposure, yet achieving high sensitivity at room temperature while maintaining mechanical compliance remains a significant challenge. Here, we report a hierarchical graphene nanowall (GNW) nanomesh that integrates material-specific transport characteristics with a three-dimensional (3D) porous architecture for enhanced gas-sensing performance. The GNW nanomesh is realized by directly growing vertically oriented graphene nanowalls on a flexible polymer nanomesh using a low-temperature plasma-enhanced chemical vapor deposition process enabled by a thermally robust parylene-coated polyimide substrate. The resulting 3D-on-3D architecture provides high accessibility of active sites and mechanically compliant pathways suitable for wearable applications. Compared to planar GNWs, the hierarchical nanomesh exhibits a sixfold enhancement in sensitivity and faster response under room-temperature operation. Particle-based simulations suggest that confined geometries within GNWs promote localized molecular trajectories and increased collision events, consistent with the observed performance enhancement. Integration into a wearable smart mask further demonstrates stable real-time detection of NO 2 over extended operation. This work highlights that combining intrinsic material transport characteristics with hierarchical nanoarchitectural design offers an effective strategy for advancing wearable gas sensing beyond conventional surface-area-driven approaches.