Enhancement of the signal-to-noise ratio in fiber-optics based SERS detection by rough-cutting the end surface

Fiber-optics based surface-enhanced Raman scattering (FO-SERS) has an unique advantage of being able to remotely detect analyte molecules because the fiber length can be adjusted as desired. However, the Raman signal of the fiber-optic material is so strong that it is an important challenge in utilization of optical fiber for remote SERS sensing. In this study, we found that the background noise signal was greatly reduced by ca. 32% compared to conventional fiber-optics with a flat surface cut. To confirm the feasibility of FO-SERS detection, silver nanoparticles labeled with 4-fluorobenzenethiol were attached onto the end surface of an optical fiber to form a SERS-signaling substrate. The SERS intensity from the fiber-optics with a roughened surface as SERS substrate was increased significantly with respect to signal-to-noise ratio (SNR) values compared to optical fibers with flat end surface. This result implies that the fiber-optics with roughened surface could be used as an efficient alternative for FO-SERS sensing platform.

Long Spiky Au-Ag Nanostar Based Fiber Probe for Surface Enhanced Raman Spectroscopy

The detection performances of noble metal-based surface enhanced Raman spectroscopy (SERS) devices are determined by the compositions and geometries of the metal nanostructures, as well as the substrates. In the current study, long spiky Au-Ag alloy nanostars were synthesized, and both core diameters and spike lengths were controlled by Lauryl sulfobetaine concentrations (as the nanostructure growth skeleton). The long spiky star geometries were confirmed by transmission electron micrograph images. Elements energy dispersive spectrometer mapping confirmed that Au and Ag elements were inhomogeneously distributed in the nanostructures and demonstrated a higher Ag content at surface for potential better SERS performance. Selected synthesized spiky nanostars were uniformly assembled on multi-mode silica fiber for probe fabrication by silanization. The SERS performance were characterized using crystal violet (CV) and rhodamine 6G (R6G) as analyte molecules. The lowest detection limit could reach as low as 10^-8 M, with a 6.23 × 10⁶ enhancement factor, and the relationship between analyte concentrations and Raman intensities was linear for both CV and R6G, which indicated the potential qualitative and quantitative molecule detection applications. Moreover, the fiber probes also showed good reproducibility and stability in the ambient atmosphere.