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Highlights • Electrostatic self-assembly of CDs@MnO 2 is used to develop a new fluorescent immunoassay. • The fluorescent immunoassay has significantly high sensitivity for the detection of amantadine in chicken.. • The alkaline phosphatase-dependent fluorescent immunoassay has a great potential in food analysis. Abstract Fluorescence immunoassays are rapid, convenient and cost-effective for the sensitive quantitation of chemical contaminants in foodstuff. In this study, a competitive fluorescence ELISA was developed for the sensitive detection of amantadine (AMD) based on the alkaline phosphatase (ALP)-triggered fluorescence "turn-on" signals. As a fluorescence substrate, carbon dots (CDs) were adsorbed onto the surface of the MnO 2 nanosheets (NSs) and formed a nanoassembly of p-CDs@MnO 2 NSs which results in the fluorescence quench of CDs. The ALP labelled on antibody could catalyze the hydrolysis of the 2-phosphoascorbic acid into ascorbic acid. The latter could then reduce and decompose the MnO 2 NSs, which was accompanied by the release of CDs from the surface of MnO 2 NSs and led to the fluorescence recovery of CDs. The change of the fluorescence intensity is related to the concentration of AMD in solution and thus could be applied to detect AMD in an ALP-based ELISA system. The fluorescent ELISA showed a linear detection for AMD in the range of 0.048 ng mL−1 to 1.1 ng mL−1 with a detection limit (LOD) of 0.035 ng mL−1. The novel fluorescent ELISA shows potential for the highly sensitive detection of AMD and other analytes in food analysis. [ABSTRACT FROM AUTHOR]

• Carbon dots-encapsulated calcium carbonate nanospheres are facilely synthesized. • Hapten-labeled MNPs are prepared and used as the nano-carrier for the immunoassay. • Fluorescent immunoassay takes a short assay time and has satisfactory performance. Analytical methods with high sensitivities and short assay times are urgently required for the screening of "zero tolerance" hazardous substances in food. Herein, we propose a fluorescent immunoassay for the highly sensitive and rapid analysis of chloramphenicol (CAP) based on carbon dots (CDs)-encapsulated CaCO 3 nanospheres and magnetic nanoparticles (MNPs). The fluorescent immunoprobes were prepared by coupling the anti-CAP antibodies to carboxymethyl cellulose-functional CDs@CaCO 3 nanospheres. Chitosan-modified MNPs with "core–shell" structures were prepared and then conjugated to the CAP hapten, acting as the nano-carrier and interface for the immunoreaction. With the assistance of MNPs, the established fluorescent immunoassay achieved the sensitive detection of CAP in chicken with a limit of detection of 0.03 μg kg−1 and recoveries ranging from 83.7%–105.0%. The analysis results of the fluorescent immunoassay were evaluated by the enzyme-linked immunosorbent assay, having a correlation coefficient of 0.981. Our work provides a rapid, facile, and reliable strategy for the highly sensitive analysis of food contaminants based on "green" fluorescent nanoprobes. [ABSTRACT FROM AUTHOR]

• Duplex FRET-based immunassay is developed using the CDs and WS 2 nanosheets. • Polyamine coated blue/green emissive CDs are prepared and coupled with the haptens. • The immunoassay achieves the simultaneous detection of AMD and CAP residues. Herein, we proposed a duplex and homogeneous fluorescent immunoassay for the simultaneous detection of amantadine (AMD) and chloramphenicol (CAP) residue in chicken breast with both high sensitivity and short assay time. The immunoassay was based on the fluorescence resonance energy transfer (FRET) between hapten-labeled carbon dots (CDs) and antibody-modified WS 2 nanosheets. To achieve the duplex FRET, polyethyleneimine-functionalized blue and green emissive CDs with separated emission were synthesized via a one-pot hydrothermal method and directly coupled with the haptens of AMD and CAP, serving as the energy donors. The antibodies were modified on the surface of WS 2 nanosheets with high quenching efficiency to construct the energy acceptor. The specific immunoreaction could trigger the efficient FRET between the donors and the acceptors, causing the fluorescence quenching of CDs. The developed immunoassay was applied to simultaneously detect AMD and CAP, having the detection limit of 0.10 ng g−1 and 0.06 ng g−1, respectively. [ABSTRACT FROM AUTHOR]