Dimensionally engineered MOF films for chemiresistive sensors

Accurate detection of trace gases is essential across a wide spectrum of fields, including smart home technologies, healthcare diagnostics, environmental monitoring, and public safety. Chemiresistive sensors have emerged as highly attractive platforms owing to their real-time response, portability, and non-contact sensing capabilities. Metal-organic framework (MOF) films, renowned for their high crystallinity, tunable porosity, and versatile chemical functionalities, represent an ideal class of materials for next-generation gas sensors. Crucially, the dimensional architecture of MOF films, including thick films, two-dimensional (2D) thin films, and three-dimensional (3D) thin films, exerts a profound influence on their sensing behaviour. From a dimensionally engineering perspective, this review comprehensively summarizes recent advances in chemiresistive MOF-based thin films, encompassing breakthrough fabrication strategies and sensing applications. We begin by reviewing early MOF-based sensors primarily utilizing thick films of pre-synthesized (nano)crystals, focusing on the effects of intrinsic features (ligands, functional groups, defects, conductivity, noble metal doping, and heterojunctions) and external stimuli (e.g., thermal, light). We then emphasize the benefits of MOF 2D thin films, whose sub-nanometer thickness and ordered porosity promote rapid analyte diffusion and efficient charge transport, significantly enhancing sensitivity and response speed. Next, we cover advances in 3D MOF architectures, including films on patterned substrates and innate 3D structures, which improve active site accessibility and conduction efficiency. Such dimensional advancements contribute to chemiresistive sensors with ultra-high sensitivity, extremely low limits of detection, and fast response/recovery. Finally, we offer a forward-looking perspective on future challenges and strategies, such as machine learning-assisted discovery, sensor arrays, high-throughput screening, in situ characterization, and integrated signal processing. This review offers a comprehensive analysis of how MOF thin films may revolutionize industrial applications by delivering tailored solutions for next-generation sensing technologies.