A comprehensive review on VOCs sensing using different functional materials: Mechanisms, modifications, challenges and opportunities

This review covers a comprehensive overview of both the basic knowledge and the advanced progress in the field of volatile organic compounds (VOCs) sensing, which is found useful in food safety, environmental air monitoring, human healthcare and other fields. Mass/electrical/optical based sensors are widely used for their accurate analysis, promising repeatability, low power consumption, low limit of detection and high sensitivity. This review begins by introducing the sensing mechanism and the types of sensors, where the metrics of different sensors are summarized. It then reports on the state-of-the-art sensing materials, from performance analysis to modification strategies. Four modification approaches namely dopant encapsulation, functionalization, ionic liquid implantation and hybridization are discussed. The advantages/disadvantages of these methods are analyzed, and the recent research achievements in VOCs sensing with these modification strategies are summarized. Emerging sensing instruments, materials and strategies, and the practical applications of VOCs sensing are addressed. Finally, the main limitations, existing challenges, possible solutions, and suggestions for future research are proposed.