Multi-functional ionic liquid (IL)-based sensor systems for detection and monitoring of volatile organic compounds (VOCs) for public health

Volatile organic compounds (VOCs) are a diverse group of low-boiling-point chemicals emitted from various sources, including biological, environmental, and industrial processes. Their detection has gained growing importance in applications ranging from noninvasive health monitoring and disease screening to air quality control and industrial process management. Ionic liquids (ILs) are a unique class of solvents that are thermally stable, nonvolatile salts with highly tunable physicochemical properties and thus have emerged as multifunctional materials for VOC gas sensing. This review provides a comprehensive overview of IL-based sensor platforms, focusing on their roles as sorbents, electrolytes, dielectric materials, and transducers across various sensing modalities, including electrochemical, gravimetric, capacitive, and chemiresistive sensing. The molecular interactions that govern VOC solubility and selectivity, such as hydrogen bonding, π-π stacking, and Lewis acid-base interactions, are examined alongside thermodynamic parameters including Henry's law constants, solvation energies, and activity coefficients. Advances in IL-functionalized composites (e.g., ionogels, IL-MOF hybrids), multivariate data analysis (PCA, SVM), and machine learning-assisted sensor arrays are also discussed. The versatility and tunability of ILs enable targeted detection and discrimination of complex VOC mixtures, positioning them as key components in next-generation VOC sensing technologies for clinical, environmental, and industrial applications.