A Novel Fluorescence Quenched Immunoassay for Sensitive Detection of Bacitracin Zinc Based on δ-FeOOH Nanosheets and Carbon Quantum Dots

Traditional fluorescent immunosensors usually suffer from high background signals in food samples, which significantly reduces their detection sensitivity. In this study, δ-iron oxyhydroxide (δ-FeOOH) nanosheets with anti-bacitracin zinc (BAC) monoclonal antibodies (mAb) were conjugated as fluorescence receptors, while amino-functionalized carbon quantum dots (CQDs) as fluorescence donors for BAC. A novel fluorescence immunoassay was developed that eliminated background noise based on the “turn on” principle. Upon introduction of BAC into the sample, the nano-assembled probe showed an increase in fluorescence recovery, leading to higher fluorescence intensity at elevated BAC concentrations. This strategy exhibited a linear response for BAC concentrations ranging from 5 to 40 ng/mL, with a limit of detection (LOD) of 2.04 ng/mL. Our findings present a promising immunological approach for the sensitive and selective detection of BAC residues in food.