Tapered Optical Fiber-Based Surface-Enhanced Raman Scattering Probes for Chemical and Molecular Sensing: Principles, Hotspot Engineering, and Applications

Tapered optical fiber-based surface-enhanced Raman scattering (SERS) probes have emerged as promising miniaturized platforms for chemical and molecular sensing by integrating optical excitation, plasmonic enhancement, and Raman signal collection within a single fiber architecture. Their enhanced light–matter interaction, compact geometry, and remote interrogation capability make them particularly attractive for in situ sensing in confined and complex environments. This review systematically examines recent advances in tapered optical fiber SERS probes, covering enhancement mechanisms, taper fabrication, plasmonic hotspot engineering, and analytical applications. Particular emphasis is placed on how taper geometry and plasmonic nanostructure organization jointly influence sensing performance. Fabrication and hotspot-engineering strategies are critically compared in terms of sensitivity, reproducibility, stability, fabrication complexity, and scalability. Representative applications in biomedical analysis, food safety, and environmental monitoring are further evaluated. Despite these advances, practical implementation remains constrained by insufficient hotspot reproducibility, quantitative reliability in complex matrices, long-term stability and antifouling performance, as well as the limited scalability of current fabrication protocols. Future progress will require balancing analytical sensitivity with reproducibility, robustness, and real-sample compatibility, while advancing deterministic hotspot engineering, selective recognition interfaces, standardized performance evaluation, intelligent spectral analysis, and Lab-on-Fiber integration. Together, these developments could accelerate the transition of tapered optical fiber SERS from laboratory-scale demonstrations to field-deployable platforms for remote and in situ molecular sensing.