In the last twenty years, optical fiber sensing technology has significantly advanced in sensor architecture, manufacturing process refinement, and system integration, establishing itself as a cornerstone of cutting-edge sensing systems. A diverse array of optical phenomena, including interference, scattering, total internal reflection, and surface plasmon resonance, are harnessed in the design of optical fiber (OF) sensors. As a novel OF sensor modality, nanostructured plasmonic OF sensors have garnered considerable interest owing to their exceptional performance and distinctive characteristics, enabling the realization of the Lab-on-Fiber concept. Since nanostructured plasmonic OF sensors embody the attributes of both conventional OF sensors and plasmonic sensors, they exhibit unique benefits and can serve as potent biochemical sensing instruments or integrated photonic components. One of the primary domains within the "Lab on Fiber" field is the use of the optical fiber in order to realize probes able to detect biomolecules at very low concentrations. A straightforward approach involves employing metal nanopatterns or nanoparticles to modify the lateral displacement or the tip of the optical fiber in order to realize an innovative metasurface or Surface-Enhanced Raman Spectroscopy (SERS) substrate on the optical fiber tip. This amalgamation aspires to create robust, adaptable, and miniaturized spectroscopic instruments for the remote and highly sensitive detection of low-concentration molecular analytes across a wide range of environments, including challenging conditions.