Integrated accurate extraction and fast detection of analyte: Capillarity-Based SERS substrate using in effluent monitoring

Highlights: • The capillarity-based SERS structure of CuO@Ag nanocapillaries (NCs) has been prepared to accurately extract molecules that dissolved in oil-phase liquid from the mixed oil/water solution. • The enhancement factor and relative standard deviation of CuO@Ag NC structure are 1.67 × 10¹¹ and 15.7 % respectively, with other Raman properties showing remarkable performance as well. • In the simulated wastewater detection test, CuO@Ag NC structure can realize the fast recognition of trace Sudan I dyes (10^-7 M) in the simulated wastewater. In order to realize integration of directional extraction and Raman detection for analytes in effluent, a capillarity-based surface-enhanced Raman spectroscopy (SERS) structure of CuO@Ag nanocapillaries (NCs) has been designed and prepared in this paper. Benefitting from the capillaries formed inside the CuO@Ag NC, probe molecules can be spontaneously transferred and concentrated from the CuO@Ag NC bottom to the top. Further processed with infrared irradiation, the CuO@Ag NC changes from amphiphilic state to hydrophobic-oleophilic state, which can accurately extract molecules that dissolved in oil-phase liquid from the mixed oil/water solution. Numerical simulations by finite-difference time domain method illustrate theoretically that the CuO@Ag NC top is also the position where the strongest electric flied located in this structure, demonstrating the integration feasibility of high-efficient extraction, enrichment and detection in one structure. Experimentally, the enhancement factor and relative standard deviation for R6G molecule of this structure are 1.67 × 10¹¹ and 15.7% respectively, with other Raman properties also showing remarkable performance. In the simulated wastewater detection test, this structure realizes the fast recognition of trace Sudan I dyes (10^-7 M) in the mixed hexane/water solution composed of both target analyte Sudan I and interferent molecule rhodamine 6G, indicating its promising prospect using in effluent monitoring.