A method of Dot immunogold filtration assay for rapid detection of Sudan I residue in food was developed. Sudan I derivate-gelatin immunogen has been synthesized using the mixed anhydride method. Polyclonal antibodies were raised against the immunogen in rabbits. The purified antibody was immobilised on the nitrocellulose membrane as the test reagent. When the sample was added into the test device, the possible Sudan I in samples and the gold-labeled Sudan I-BSA conjugate which was added subsequently into the test device will competitively capture the immobilised antibody. The more Sudan I present in the samples, the more effective competition reaction with gold-labeled Sudan I-BSA occurred. A visible red dot shows a negative result in the read-out zone, and vice versa. Results showed that the detection limit was 0.8 µg/mL in chili powder. Quantitative analysis of Sudan I could be achieved between 0.2 µg/mL and 1.0 µg/mL. Compared with HPLC methods, the results showed a good correlation with a square of correlation coefficient of 0.941. Low cross-reactivity was found among other Sudan dyes. The analysis could be completed in shorter time, suitable for rapid detect Sudan I residue in food and preliminary screening detections for abundant samples.
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