Dispersive Liquid–Liquid\nMicroextraction (DLLME) Coupled\nwith Droplet Evaporation\non an Omniphobic Nano/Micro Structured Porous Microfiber Membrane\nfor Surface-Enhanced Raman Spectroscopy

This study demonstrates an ultrasensitive method for\nsurface-enhanced\nRaman spectroscopy (SERS) based on dispersive liquid–liquid\nmicroextraction (DLLME) coupled with droplet evaporation on a functionalized\nomniphobic microfiber membrane. The omniphobicity of the membrane\nwas achieved by the fabrication of fractal structures using silica\nnanoparticles and lowering surface energy. The approach involves the\npreconcentration of the analyte in a ternary mixture of water–oil–ethanol,\nfollowed by collecting microemulsion droplets in an omniphobic porous\nmicrofiber membrane. A supraparticle of plasmonic nanoparticles formed\nfrom droplet evaporation on the membrane acts as hotspots for SERS\ndetection. This method achieves exceptionally low detection limits\nof 10<sup>–6</sup>–10<sup>–14</sup> M for four\nnonvolatile and three volatile analytes of significance to food safety\nand environment after oil spill. The intensity of SERS signals depends\non the partition coefficient of the analyte in water and oil microdroplets,\nthe response of functional groups in the chemical structure of the\nanalytes to Raman scattering, and the wetting properties of the microfiber\nmembrane. The preparation method demonstrated in this work may have\nbroad applications in the detection of pesticides in environmental\nmonitoring, pharmaceutical waste, and hydrocarbon pollutants.