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Microstructure fibers, integrating microfluidic channels and light guidance in one fiber, enable three-dimensional surface-enhanced Raman scattering (SERS) detection for large signal accumulation. However, the available fiber SERS probes are complicated to prepare and they are not reusable. In addition, light interacts with analytes in a form of an evanescent field, which is very weak. In this paper, we developed a SERS platform based on suspended-core photonic crystal fibers decorated with Ag/ZnO nanocomposites on the inner surface for direct, ultrasensitive, and reusable analyte detection. The unique configuration not only transfers a core-localized field to the liquid interface to greatly enhance the light–analyte interaction but also facilitates charge transfer to further improve the SERS detection sensitivity and degradation efficiency. The detection limit of crystal violet solution is 10–13 M, and the enhancement factor reaches 1011. The relative standard deviation is as low as 5.4%, ensuring the reproducibility of SERS detection. The probe has good photocatalytic performance and can degrade molecules under ultraviolet-light illumination within 20 min. This ultrasensitive and reusable SERS probe shows great application potential in rapid and in situ liquid detection. [ABSTRACT FROM AUTHOR] more...

Surface-enhanced Raman scattering (SERS) is a rapid and nondestructive spectroscopic method for trace detection. The enhancement based on both electromagnetic and chemical mechanism requires the molecules to be in close contact with the SERS-active material. Therefore, it is difficult to detect trace amounts of molecules in liquid directly. In this paper, graphene oxide (GO) and Ag nanoparticles (AgNPs) are uniformly modified on the inner wall of the capillary. GO can provide chemical enhancement by adsorbing the analyte onto its flat surface and producing efficient charge transfer resonance with the analyte. AgNPs can provide strong localized surface plasmon resonance for electromagnetic enhancement, while capillary can shorten the molecular enrichment time and provide long light–analyte interaction length. The synergism of GO, AgNPs, and capillary makes the optofluidic platform have the ability of ultrasensitive and real-time detection. The detection limit of Rhodamine 6G and thiram is as low as 10–12 and 10–10 M, respectively, and the enhancement factor is as high as 0.9 × 1010 and 108, which indicates that the SERS-active capillaries have great potentials in real-time ultratrace detection of water environment pollutants. [ABSTRACT FROM AUTHOR] more...

Surface-enhanced Raman scattering (SERS) has been widely used owing to its high sensitivity and rapid response. In particular, 3D SERS-active platforms greatly extend the interaction area and ensure the ability to directly detect trace amounts of molecules in liquids. A silver-coated capillary, with the ability of liquid sampling and light guiding, provides a new platform for high-performance SERS substrates. In this paper, the silver mirror reaction was used for coating silver on the outer wall of the capillary. PDMS was used as a coating material to protect the silver film. Because of the silver coating, Mie scattering and Raman scattering in the liquid channel can be refocused and reflected back which greatly reduces the propagation loss and extends the interaction length. An enhancement factor as high as 10 8 and a detection limit of 10 -10 M of rhodamine 6G in aqueous solution have been achieved. Moreover, the SERS intensity is homogeneous across the end face of the liquid channel, with the relative standard deviation (RSD) value changing within 7%. The large area and high homogeneity greatly reduce the requirement of light coupling precision and liquid injection pressure. Using a common flange optical fiber connector, the capillary can be simply connected and aligned with a multimode fiber with a detection limit of 10 -8 M. The experiment results show great potential for the development of an optofluidic integrated system in the future., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.) more...

The development of Surface Enhanced Raman Scattering (SERS) promotes the wide application of Raman spectroscopy in chemical and biomolecular detection. SERS detection relies on analytes in close contact with the metallic surface, and therefore direct molecular trace detection in the liquid phase is difficult. In this paper, static liquid phase SERS detection was performed simply using a capillary without pre-functionalization. Gold nanoparticles (AuNPs) with an optimized size ensure localized surface plasmons in resonance with the exciting laser light. Grazing incidence and multimode interference in the capillary ensure that the longitudinal Raman signal is effectively excited and accumulated. An enhancement factor as high as 10 8 and a detection limit of 10 -9 M of crystal violet in aqueous solution have been achieved., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.) more...