Confined Gaussian-distributed electromagnetic field of tin(II) chloride-sensitized surface-enhanced Raman scattering (SERS) optical fiber probe: From localized surface plasmon resonance (LSPR) to waveguide propagation

Surface-enhanced Raman scattering (SERS) induced by largely enhanced electromagnetic (EM) field provides a solid and promising avenue for ultrasensitive molecular detection. Here, a confined Gaussian-distributed EM field for SERS fiber probe with two influencing factors (localized surface plasmon resonance (LSPR) of silver and waveguide propagation of optical fiber) are proposed for the first time. SERS fiber probes with high sensitivity and good reproducibility were synthesized via a novel SnCl2 sensitization aided solvothermal method. The influencing factors and EM field distribution are investigated experimentally and theoretically. The LSPR-induced EM enhancement is observed. By introducing a sensitization procedure, silver particles show smaller sizes and narrower interparticle gaps, significantly influencing the LSPR and EM enhancement of the SERS fiber probe. Moreover, a unique waveguide-propagation-induced EM enhancement is brought up. Waveguide propagation modes of optical fibers influence the intensity and enhancement area of EM field. Further, the EM field distribution of SERS fiber probe is studied. It exhibits a concentrically-increased intensity gradient that is confined in core area with maximum enhancement at fiber core center. This confined Gaussian-distributed configuration of EM field on SERS fiber probe facet is induced by the LSPR of plasmons and waveguide propagation of optical fiber. (C) 2020 Elsevier Inc. All rights reserved.