Highly Sensitive Molecular Detection Using Tapered Fiber with Ag Nanoparticle Self-Assembled Film for Confined-Enhanced Raman Spectroscopy

The synergistic combination of tapered fibers and surface-enhanced Raman spectroscopy (SERS) technology capitalizes on the unique light-field compression and evanescent wave enhancement properties on the near surface of conical structures, generating highly localized plasmonic fields in the whole tapered region that substantially improve detection sensitivity. The incorporation of confined-enhanced Raman spectroscopy (CERS) technology may enhance both detection sensitivity and signal uniformity through its molecular anchoring effect. In this study, we developed a tapered-fiber-coated CERS platform (TF-CERS) based on CERS technology. By employing a vertical dip-coating method, we achieved a uniform modification of silver nanoparticles (Ag NPs) on the fiber tip. Additionally, a NaCl-induced packaged active shell was employed to effectively anchor target molecules, resulting in significantly enhanced signal stability. The TF-CERS platform demonstrated an ultralow detection limit of 4.37 × 10^-14 M for crystal violet (CV), with an RSD of 5.99%. Furthermore, the TF-CERS platform achieved highly sensitive multiplex detection in real water samples, successfully identifying both typical dye molecules such as rhodamine 6G (R6G) and malachite green (MG) and critical pesticide residues, including thiram and carbendazim, with excellent analytical performance. The proposed TF-CERS technology provides a highly sensitive and reliable solution for environmental pollution monitoring, holding significant potential for practical applications.