Recent advances in lignin-based sensors: Structure-guided material design, sensing mechanisms, and emerging applications: A review.

Lignin, the most abundant renewable aromatic polymer in nature, is increasingly being explored as a versatile precursor and functional component for sustainable sensor materials. Its rich interfacial chemistry, tunable structure, antioxidant character, and compatibility with nanomaterials make it particularly attractive for the construction of electrochemical sensors, optical sensors, biosensors, gas sensors, humidity sensors, pressure sensors, and strain sensors. This review examines recent progress in lignin-based sensors from a structure-property-function perspective. Particular attention is given to how phenolic hydroxyls, methoxy groups, carbonyl/carboxyl functionalities, aromatic domains, and supramolecular interactions govern analyte binding, interfacial adhesion, ion transport, redox behavior, and mechanical adaptability. Major material-engineering strategies, including chemical modification, nanoparticle formation, hydrogel design, carbonization, and hybridization with conductive polymers, carbon nanomaterials, metal nanoparticles, and MXenes, are discussed in relation to sensing mechanisms and device performance. Representative applications across different sensor categories are critically assessed. The remaining barriers to practical deployment, notably feedstock variability, weak structure-performance correlation, incomplete mechanistic understanding, and scale-up limitations, are also discussed together with future directions in more sustainable manufacturing, multifunctional integration, wearable electronics, and potentially biodegradable sensing platforms. By clarifying how lignin chemistry can be translated into sensing function, this review aims to support the rational development of lignin-enabled sensor technologies.