Large-scale well-separated Ag nanosheet-assembled micro-hemispheres modified with HS-beta-CD as effective SERS substrates for trace detection of PCBs

Large-scale well-separated Ag nanosheet-assembled micro-hemispheres with similar size and morphology were achieved on bare commercial ITO substrates via simple electrodeposition in a mixed aqueous solution of citric acid and AgNO3. It was found that appropriate electrodeposition current density and citric acid concentration are critical to the formation of well-separated nanosheetassembled micro-hemispheres with similar size and morphology. The well-separated Ag nanosheetassembled micro-hemispheres with similar size and morphology ensure the good surface-enhanced Raman scattering (SERS) signal reproducibility from different micro-hemispheres, and the sufficient sub-10 nm gaps on the nanosheet-assembled micro-hemispheres guarantee the high SERS sensitivity. By further modifying the Ag nanosheet-assembled micro-hemispheres with mono-6-thio-beta-cyclodextrin (HS-beta-CD), the SERS detection limit of 3,3',4,4'-tetrachlorobiphenyl (PCB-77) can be further reduced, and two different polychlorinated biphenyl (PCB) congeners of 2-chlorobiphenyl (PCB-1) and PCB-77 in a mixed solution can be distinguished, indicating that the large-scale well-separated Ag nanosheet-assembled micro-hemispheres modified with HS-beta-CD may have great potential as effective SERS substrates for rapid trace detection of PCBs.