Fabrication of a Novel Transparent SERS Substrate Comprised of Ag-nanoparticle Arrays and its Application in Rapid Detection of Ractopamine on Meat

Surface-enhanced Raman spectroscopy (SERS) is an emerging new analytical tool that boasts the feature of high detection sensitivity and molecular fingerprint specificity, attracting increased attention and showing promise for various applications in many areas including food industry. But in practice, special pretreatments of samples are generally required and to some extent have restricted the extension of its applications, particularly in examining analytes in opaque food. In this work, we put forward a new approach to fabrication of transparent SERS substrates which could be used to probe residual ractopamine on pork meat directly without pretreatment of the meat samples. The SERS substrate was fabricated based on anodic aluminum oxide (AAO) template, from which a conical-pore-AAO template with regularly ordered Al2O3 nanotips on the surface was formed after multistep process of anodization and etching, followed by removal of remaining aluminum and sputtering silver nanoparticles (Ag NPs) on the nanotips on the surface. The as-fabricated transparent SERS substrate could detect ractopamine in solution with a detection limit as low as 10(-8) M, which is lower than the provision of the international standard concentration of 10 mu g/L, and was confirmed to be sensitive enough for detecting trace ractopamine on meat directly. Therefore, this work not only demonstrates an easy approach to fabrication of a novel transparent SERS substrate for detection of residual ractopmine in meat but also may provide a convenient and effective solution to the problem of directly measuring trace chemicals on the surface of opaque food.