A Review of High-Sensitivity SERS-Active Photonic Crystal Fiber Sensors for Chemical and Biological Detection

This review critically surveys the emerging integration of Surface-Enhanced Raman Scattering (SERS) with photonic-crystal fibers (PCFs) for chemical and biological detection, an area still scarce in the literature. SERS exploits electromagnetic and chemical enhancement to overcome the intrinsic weakness of Raman scattering, while PCF offers low transmission loss and a strong evanescent field that further amplify the signal. The structural designs of PCF, encompassing solid-core and hollow-core variants, are discussed and their respective advantages in different sensing scenarios are presented. Applications in chemical detection, biomedicine, and explosive identification are detailed, demonstrating the versatility and potential of PCF-SERS sensors. Future efforts will focus on robust PCF geometries that guarantee stable and reproducible signals, AI-driven spectral algorithms, hybrid fibre architectures and scalable manufacturing. These advances are expected to translate PCF-SERS from bench-top demonstrations to routine deployment in environmental monitoring, clinical diagnostics and food-safety control.