Intrinsically Breathable and Flexible NO₂Gas Sensors Produced by Laser Direct Writing of Self-Assembled Block Copolymers

The surge in air pollution and respiratory diseases across the globe has spurred significant interest in the development of flexible gas sensors prepared by low-cost and scalable fabrication methods. However, the limited breathability in the commonly used substrate materials reduces the exchange of air and moisture to result in irritation and a low level of comfort. This study presents the design and demonstration of a breathable, flexible, and highly sensitive NO2 gas sensor based on the silver (Ag)-decorated laser-induced graphene (LIG) foam. The scalable laser direct writing transforms the self-assembled block copolymer and resin mixture with different mass ratios into highly porous LIG with varying pore sizes. Decoration of Ag nanoparticles on the porous LIG further increases the specific surface area and conductivity to result in a highly sensitive and selective composite to detect nitrogen oxides. The as-fabricated Ag/LIG gas sensor on a flexible polyethylene substrate exhibits a large response of -12‰, a fast response/recovery of 40/291 s, and a low detection limit of a few parts per billion at room temperature. Integrating the Ag/LIG composite on diverse fabric substrates further results in breathable gas sensors and intelligent clothing, which allows permeation of air and moisture to provide long-term practical use with an improved level of comfort.