Fluorescence immunoassay based on magnetic separation and ZnCdSe/ZnS quantum dots as a signal marker for intelligent detection of sesame allergen in foods.

To detect sesame allergens, a novel fluorescent immunoassay incorporating a magnetic separation step has been developed via two measurement devices: a fluorescence spectrophotometer and a smartphone equipped with a color reader. Sesame allergen monoclonal antibody (Ab) was covalently bonded with quantum dots (QDs) to act as a signal probe. The capture probes were synthesized as sesame allergen (SA) modified carboxyl-functional magnetic polystyrene microspheres (MPMs). Analytical variables such as the amount of modified SA, the reaction volume of the QDs-Ab, the ionic strength, the pH, and the incubation time of the reaction were optimized. The analytical range and the limit of detection (LOD) of the spectrophotometer-based assay were 80-640 μg/L and 12.75 μg/L, respectively. The analytical range and the LOD with smartphone read-out were 80-640 μg/L and 10.15 μg/L, respectively. Furthermore, the developed assay using the fluorescence spectrophotometer and the smartphone read-out was successfully applied to field testing of SA in solution extracts of biscuits, bread, almond beverage, and energy bars with acceptable results. The recovery rates were in the range 89-108%. It was concluded that the new assay may be used for rapid sesame allergen testing in the laboratory and in the field.