Strategies for formaldehyde sensing and their applications.

Formaldehyde (HCHO) is a widespread toxic contaminant and a recognized human carcinogen. Its pervasive presence raises significant concerns for public health and environmental safety. The development of reliable sensing technologies for HCHO is therefore of paramount importance. Herein, various strategies for HCHO sensing are systematically summarized from the perspective of sensing mechanisms and materials design. Based on diverse interaction mechanisms, including imine (Schiff base) formation, the 2-aza-Cope rearrangement reaction, leuco-fuchsin reaction, cyclization reactions, Pictet-Spengler reaction, oxidation reactions, hydrogen bonding, and supramolecular self-assembly, representative HCHO sensing systems are classified and discussed in detail, such as optical molecular probes, electrochemical transducers, metal oxide semiconductor (MOS) chemiresistors, as well as other functional materials. Their sensitivity, selectivity, response characteristics, and practical limitations are comprehensively summarized and thoroughly analyzed. Special emphasis is placed on the mechanism, structure, and response models in enhancing HCHO capture and signal transduction. Furthermore, recent representative cases in practical applications, encompassing real-time environmental monitoring, food safety assessment, and advanced bioimaging, are discussed. Finally, the prospects for the strategic design of HCHO sensors are delineated herein, with a view toward meeting the demands of real-world deployment.