“…Over the past decade, various strategies for detecting VOCs, such as molecular engineering, 56 surface functionalization (e.g., receptors 57 and porous materials 58 ), morphology control (e.g., porosity 59 and grain boundary 60 ), and heterojunction, 61 have been reported. Among the many known VOCs (e.g., ammonia, 62−66 nitrogen dioxide (NO 2 ), 67−70 hydrogen sulfide (H 2 S), 71,72 toluene, 73 acetone, 74 and formaldehyde 59 ), NO 2 is one of the most intensively targeted gases because it can directly damage human health at ppm levels; moreover, NO 2 is the cause of many environmental problems. To effectively monitor NO 2 gas, Jin et al demonstrated an ionotronic gas-sensing sticker (IGS) that showed particularly high selectivity for NO 2 and can be used as a wearable gas-sensing platform.…”