As a strong carcinogen to humans,acid orange Ⅱ is forbidden to be added as an additive into foodstuff.Because the foods colored with acid orange Ⅱ showed stable and colorful appearance,acid orange Ⅱ is broadly utilized by illegally producers for their low costing.Currently available analytical methods for acid orange Ⅱ are mainly based on fluorescence and liquid chromatography,which are time-consuming and tedious as acid orange Ⅱ has to be extracted from the samples before determination.For efficient detection and insurance of food safety,it is urgent to develop fast and low-cost in situ assay methods for field detection of acid orange Ⅱ on foods.In this study,shell-isolated Au@SiO2 nanoparticles is prepared for detecting acid orange Ⅱ on food.Gold colloidal solution with good size distribution（50 nm） is prepared using the standard sodium citrate reduction method,followed by coating a thin layer of SiO2on Au nanoparticle surface.This shell-isolated Au@SiO2 is obtained by the addition of active silica to the gold colloidal solution,with the（3-aminopropyl）trimethoxysilane（APTMS） as the coupling agent at pH 8.5.By regulating the amount of the active silica,the Au@SiO2 with different silica shell thickness is synthesized.Ultraviolet-visible spectroscopy（UV-Vis） and transmission electron microscope（TEM） are employed to characterize the optical property and morphology of the as-synthesized Au@SiO2 nanoparticles.The amount of the active silica added in preparation of the Au@SiO2is optimized through comparing the surface enhanced Raman scattering（SERS） intensity of acid orange Ⅱ,using the synthetic Au@SiO2 structure as the SERS substrate.Under the optimized experimental conditions,acid orange Ⅱ on the Si wafer can be detected at concentrations below 0.17 mg/L.The feasibility of the proposed method for detecting acid orange Ⅱ in real samples is verified by spreading the Au@SiO2 nanoparticles on the surface of the watermelon seeds stained with acid orange Ⅱ.Results showed that this novel method is capable of detecting 0.01 mg/g acid orange Ⅱ stained on the watermelon seeds.This proposed method was applied to assay sunflower seeds and watermelon seeds purchased from local stores.It is expected that this proposed method is applicable for in situ detection of acid orange Ⅱ on the surface of other food samples.%以具有核壳结构的Au@SiO2纳米颗粒为基底,建立了一种以表面增强拉曼（SERS）原位、快速检测食品中非法添加剂酸性橙Ⅱ的新方法.研究了活性硅加入量对所形成的Au@SiO2纳米颗粒的SERS活性的影响,制备了具有最佳SERS活性的Au@SiO2,并以此为SERS基底建立了酸性橙Ⅱ的分析方法,可实现0.17 mg/L酸性橙Ⅱ的SERS检测.将合成的Au@SiO2滴加到瓜子表面后,可以实现对瓜子表面酸性橙Ⅱ浓度为0.01 mg/g时的SERS检测,能够满足食品中酸性橙Ⅱ的测定要求,有望用于瓜子及其它可能被非法添加该物质的食品的现场、快速检测.
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