Advancements in optical fiber coatings and functionalization for chemical and biological sensing applications

Recent advances in optical fiber engineering have enabled the transformation of conventional fibers into sophisticated platforms for chemical and biological sensing. Innovations in coating technologies-incorporating polymers, metals, nanoparticles, and hybrid nanocomposites, have significantly enhanced light-matter interactions at the fiber interface, thereby improving analytical sensitivity and performance. Polymeric coatings provide chemical tunability and mechanical flexibility, while metallic films enable plasmonic-based refractive index sensing with high responsiveness. In parallel, the integration of nanoparticles and nanocomposite materials introduces tailored optical properties and multifunctional behavior, expanding the capabilities of fiber-based sensing systems. Complementary surface functionalization strategies, including self-assembled monolayers and molecular imprinting have further advanced the field by enabling the controlled immobilization of biorecognition elements such as enzymes, antibodies, and aptamers. These approaches confer high selectivity and stability, facilitating the development of next-generation optical fiber sensors for the detection of gases, volatile organic compounds, biomarkers, pathogens and genetic targets. This review summarizes recent progress in coating materials, surface functionalization methods, and optical transduction mechanisms for fiber-optic chemical and biological sensors. Particular emphasis is placed on the relationship between coating morphology, sensing performance, and practical challenges, including coating instability, signal drift, reproducibility, and operation in complex sample environments. Emerging trends in distributed sensing and artificial intelligence-assisted signal processing are also discussed as promising directions for next-generation intelligent optical fiber sensing systems.