Lab-on-tip photonic crystal fiber SERS probe for trace environmental monitoring.

This work focuses on designing a lab-on-tip surface-enhanced Raman scattering (SERS) probe. The probe is implemented based on a polarization-maintaining D-shaped photonic crystal fiber coated with a 50 nm thin layer of gold nanoparticles (AuNPs). The D-shape configuration enables the efficient coupling between the light and analyte, whereas the gold film ensures localized surface plasmon (LSP) enhancement. In this study, toluene was used as a model analyte to evaluate the sensing efficiency of the probe. The LOD value obtained via the gold-coated fiber probe was 3.3 × 10-13 M, which is eight orders of magnitudes lower than conventional Raman spectroscopy and four orders of magnitudes lower than the uncoated fiber. The behavior of the SERS probe showed a non-linear response with a Langmuir type shape, which confirms the strong affinity of toluene toward gold. The probe demonstrates very good values of repeatability (RSD = 4.2%), reproducibility (8.7%), and stability (<12% signal loss over 14 days). These findings highlight the potential of the proposed lab-on-tip SERS probe as a highly sensitive, reliable, long-term stable, and compact platform for ultra-trace chemical sensing in real-world applications.