Metal Oxide Nanosystems As Chemoresistive Gas Sensors for Chemical Warfare Agents: A Focused Review

The early and efficient detection of chemical warfare agents (CWAs), hazardous compounds resulting in fatal and irreversible health damages, is an issue of primary importance for security safeguard. Despite the efforts undertaken to date, the quest of lower detection limits, higher selectivity/stability, and faster recognition still represents a main bottleneck to effectively counteract such dreadful threats. This review aims at providing a survey on the developments undertaken in chemoresistive gas sensors based on metal oxide nanosystems for CWA recognition. The sensing mechanisms proposed in the literature, as well as the main reasons underlying the performance enhancement for functionalized/composite systems, are reviewed and discussed. The work summarizes key results achieved so far, and attempts to provide guidelines to overcome the main open problems. Efforts are devoted to delivering information on material properties/performance interplay, highlighting challenges in their fabrication and functional characterization. In fact, despite the advances made, a rational design and understanding of interfacial properties, as well as a perfect control over system growth, mandatory for commercial applications, are still missing. At the conclusion, a brief outlook on development prospects for future advancements is presented, endeavoring to provide a vision on the next necessary steps for an eventual technological implementation.