Аннотация:A novel lateral flow immunoassay based on the use of two kinds of conjugated gold nanoparticles’ preparations was developed and applied to the detection of the toxic food colorant Sudan I. The gold nanoparticles were conjugated with monoclonal antibodies specific to Sudan and a Sudan-ovalbumin conjugate. Before the immunochromatographic process, the two conjugates were incubated with a tested sample. The results obtained a direct calibration curve for the detection of low-molecular-weight antigen, in contrast to common reverse concentration dependencies. In the absence of the target compound, minimal coloration of the test line was observed. An increase in the Sudan content led to staining and the appearance of a test line, which could be observed by the naked eye. The total duration of the assay is 15 minutes. The visual limit of Sudan I detection was 0.25 ng/mL, and the instrumental limit of detection (LOD) was 7.6 pg/mL. These values were at least three-four points lower than the established permissible level of the contaminant content in foodstuffs. This reserve in sensitivity provides the possibility of working with highly diluted samples and thus excludes the influence of their matrixes on the assay results. The direct dependence of the coloration on the concentration of Sudan I in the proposed assay means it is easy to identify the presence of the contaminant at extremely low concentrations. The common nature of the proposed approach allows its use in lateral flow immunoassays of different compounds.