Fiber Optic Biosensors Exploiting Localized Surface Plasmon Resonance From Nonspherical Nanostructures: A Review

Fiber optic biosensors have emerged as powerful platforms for label-free detection due to their high sensitivity, compactness, chemical stability, and compatibility with remote and multiplexed operation. The integration of plasmonic nanostructures with optical fibers enables localized surface plasmon resonance (LSPR)-based transduction, enhancing detection performance through strong light-matter interactions at the nanoscale. In this context, while spherical gold nanoparticles have been extensively investigated, growing attention is now directed toward non-spherical geometries that offer improved spectral tunability and surrounding medium refractive index (SRI) sensitivity. This review provides a comprehensive assessment of recent advances in fiber optic biosensors exploiting LSPR from unconventional nanostructures, including nanorods, nanostars, nanotriangles, nanodiscs, and hollow nanoparticles. The discussion highlights how nanoparticle morphology governs resonance characteristics, SRI sensitivity, and detection limits across different fiber architectures from the last 15 years. Emphasis is placed on the entire development chain, covering fiber transducer design, nanostructure synthesis and characterization, surface functionalization, and bio-recognition strategies. Finally, the review offers a comprehensive framework for critically comparing the principal classes of non-spherical plasmonic nanostructures integrated with optical fibers, discussing their advantages, limitations, technology maturity, and future research directions toward novel biosensing systems.