Direct Nucleation of Hierarchical Nanostructures on Plasmonic Fiber Optics Enables Enhanced SERS Performance

Abstract An innovative fabrication method is presented to achieve bottom‐up in situ surface‐overstructured Au nanoislands (NIs) with tunable grades of surface coverage, elongation, and branching, directly on micro‐optical fibers for sensing applications. These all‐in‐gold hierarchical nanostructures consist of NIs coated with surface protrusions of various morphologies. They are created in solution using a selective seeded growth approach, whereby additional gold growth is achieved over Au NIs formerly developed on the fiber facet by a solid‐state dewetting approach. The morphology of nanosized surface‐NI overstructuring can be adjusted from multi‐dot‐decorated Au NIs to multi‐arm‐decorated Au NIs. This engineering of optical fibers allows for improved remote surface‐enhanced Raman spectroscopy (SERS) molecular detection. By combining solid‐state dewetting and wet‐chemical approaches, stable in‐contact deposition of surface‐overstructured NIs with the optical fiber solid substrate is achieved, alongside precise control over branching morphology and anisotropy extent. The fiber‐optic probes engineered by surface‐overstructured NIs exhibit outstanding sensing performance in an instant and through‐fiber detection scheme, achieving a remarkable detection limit at 10 −7 M for the R6G aqueous solution. These engineered probes demonstrate an improved detection limit by one order of magnitude and enhanced peak prominence compared to devices solely decorated with pristine NIs.