Fast multiphase analysis: Self-separation of mixed solution by a wettability-controlled CuO@Ag SERS substrate and its applications in pollutant detection

Surface-enhanced Raman spectroscopy (SERS) is widely used in chemical analysis, with very promising application prospects in daily life. However, there are still lots of problems in actual operation, for instance, pollutant detection from sewage, in which the analyte is often dispersed in nonhomogeneous solutions, leading to inaccurate Raman signal collection. Adjusting surface wettability to realize selective self-separation of multiphase liquids in situ on SERS substrate is an effective and challenging approach. In this work, a complex of CuO@Ag nanowires on Cu mesh modified by different wettability, converting from hydrophilic to hydrophobic by simple infrared illumination, is prepared as a multifunctional SERS substrate. Benefitting from the controllable wettability of the substrate, the multiphase solution can be self-separated and adsorbed at the two opposite terminals of it, and the 10 −9 M of malachite green and 10 −5 M of thiram used as two kinds of probe molecules can be separately detected at these two terminals. In addition, after fully hydrophobic modification, the substrate can be also used to extract the organic phase in the ‘water/oil’ mixture and perform in situ detection of the probe molecules in the ‘oil’.