Ultrasensitive detection of Sudan I in food samples by a quantitative immunochromatographic assay.

An immunochromatographic assay (ICA) based on surface-enhanced Raman scattering (SERS) for ultrasensitive determination of Sudan I in food samples was reported. Gold-silver core-shell bimetallic nanorods (referred to as Au@Ag NRs) were synthesized, characterized and used as the substrate for preparation of the ICA. Polyclonal antibody against Sudan I was immobilized on the surface of the Au@Ag NRs carrying the Raman reporter 5,5'-dithiobis (2-nitrobenzoic acid). The Raman scattering intensity on the test line was used for quantitation of Sudan I. The assay was completed in 15 min. IC50 and limit of detection (LOD) were 30 pg mL-1 and 0.2 pg mL-1, respectively. There was no cross-reactivity (CR) of the assay with Sunset Yellow, Lemon Yellow and Brilliant blue FCF, but only 3.53%-9.74% CR with Sudan II, III and IV. The recoveries of Sudan I from spiked food samples were in the range of 88.9-107.6% with relative standard deviation of 3.7-8.7% (n = 3).