LAUSR

A simple indirectly competitive ratiometric fluorescent immunoassay was designed based on fluorescein amidite (FAM)-DNA–functionalized CdSe/ZnS quantum dots (QDs) for the sensitive determination of tetrabromobisphenol A (TBBPA). At the detection system, catalase (CAT) was labeled on the secondary antibody (Ab 2 ), which served as a controller of the H 2 O 2 concentration. After the competitive binding step, the emitted red fluorescence (excitation at 490 nm) from FAM-DNA–functionalized CdSe/ZnS QDs could be effectively quenched by the H 2 O 2 added. Under the optimized conditions, the limit of detection (LOD) reached 0.118 μg/L with a linear range of 0.34–45.34 μg/L, which was approximately 1 order of magnitude lower than that by HRP-based traditional ELISA. Furthermore, the combination of the dual-output ratiometric fluorescence assays with ELISA improved the inherent built-in rectification to the environment, which brought about satisfactory accuracy and precision (recoveries, 83.16–112.4%; CV, 2.42–7.28%), indicating great potential for the determination of trace TBBPA from food and environmental samples. Graphical abstract