In-Situ Vertical-Contact Engineering of Laser-Induced Graphene Nanotips for Ultra-Sensitive Humidity Sensors

Advancements in laser-induced graphene (LIG) technology enables the streamlined fabrication of 3D porous graphene-based humidity sensors. However, conventional LIG-based humidity sensors employing lateral-contact configurations often exhibit limited responsivity, owing to their partially exposed structures and dominant subsurface current pathways. This study presents a novel vertical-contact architecture that utilizes vertically aligned LIG nanotips for ultra-sensitive humidity detection. Single-pulse laser irradiation induces localized growth of the LIG nanotips, simultaneously forming in-situ vertical contacts with both the top and bottom graphene electrodes. This fully exposed structure provides a highly efficient sensing interface. By adjusting the air-gap height between the electrodes, the sensor operates in two distinct modes: Contact Mode, which achieves high responsivity (40%) via resistance modulation by water adsorption, and Remote Mode, which leverages field ionization to achieve exceptional responsivity (14 000%). The sensors demonstrate rapid response and recovery times (<1 s), excellent stability, and high gas selectivity. Integration into wearable face masks enables real-time respiratory monitoring, including hyperventilation and high-frequency breathing (up to 156 bpm), without signal degradation. This study presents a simple and scalable strategy for fabricating high-performance humidity sensors for next-generation wearable healthcare applications.