Waveguide-based Raman enhancement strategies

Waveguide-enhanced Raman scattering (WERS) is a powerful branch of enhanced Raman technologies that has gained significant progress in recent years because of its advantages, such as reproducibility and robustness. As a complementary tool to surface-enhanced Raman spectroscopy (SERS), WERS provides a powerful solution for reproducible quantification of analytes. According to different Raman enhancement mechanisms, five major WERS implementation strategies, namely, (1) single-mode dielectric waveguide, (2) liquid core waveguide, (3) metal cladding waveguide, (4) resonance mirror waveguide, and (5) double metal cladding waveguide, are classified and described in detail in this review. The flexibility of WERS structures makes them easy to be integrated with 2D devices to obtain a complete on-chip detection scheme, allowing the WERS chip to combine excitation, detection, and data analysis in integrated chips, providing a powerful prospect for real-time and on-site analysis of target samples. This article highlights the principles, implementations, and application scenarios of WERS techniques and evaluates their advantages and limitations, respectively. Finally, the strengths and weaknesses of WERS techniques are summarized, and promising future applications are proposed. This review provides a panoramic view for researchers interested in waveguide-enhanced Raman technology.