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

Abstract 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.