Large-scale uniform Ag-NW tip array with enriched sub-10-nm gaps as SERS substrate for rapid determination of trace PCB77

Ag-nanowire (Ag-NW) tip arrays with high density sub-10-nm gaps have been achieved via anodic aluminum oxide (AAO) template-assistant approach, and exhibit superior surface enhanced Raman scattering (SERS) performance. The Ag-NW tip arrays were fabricated via the following procedures. Firstly, the pore walls of the AAO were thinned to the sub-10-nm scale, and then a layer of Ag thin film was deposited on the AAO via silver mirror reaction. Subsequently, a layer of gold (Au) film was coated on the Ag film via ion-beam evaporation to serve as the electrode for the electrodeposition growth of Ag-NWs. Finally, the Ag-NW tip arrays with sub-10-nm gaps were exposed from the AAO template by physical milling and a subsequent chemical etching. The SERS activity of the as-fabricated substrate is verified by measuring the probe molecules of R6G and polychlorinated biphenyls (PCBs). To further improve the detection sensitivity for PCBs, the substrate was modified with β-cyclodextrin to increase its efficiency of capturing PCBs molecules. As a result, the as-fabricated SERS substrate can be utilized to measure trace 3,3′,4,4′-tetrachlorinated biphenyls (PCB77) with a concentration as low as 1 × 10−10 M.