Multifunctional bacteria-derived tags for advancing immunoassay analytical performance with dual-channel switching and antibodies bioactivity sustaining.

Abstract Constructing multifunctional immunochromatographic assays (ICA) carriers with multiple signals and retaining bioactivity of monoclonal antibodies (mAbs) are conducive to the sensitive and accurate point-of-care testing (POCT). To fulfill this pressing need, a microorganism-based microsphere mediated dual-modal ICA (DICA) was developed for sensitive and reliable detection of zearalenone (ZEN). As the key to the biosensor, a superb biotag with an intact coccus morphology was designed based on Staphylococcus aureus biosynthesized quantum dots incorporating Ru(bpy)32+ (SAQDsRu), in which SA offered a specific recognition capacity for Fc region of mAbs, QDs endowed a naked-eye discernible colorimetric signal on the SA, and robust fluorescence signal that remedied for the insufficient brightness of QDs was derived from Ru(bpy)32+. The characterization of SAQDsRu-labeled mAb (SAQDsRu-mAb) probe demonstrated strong luminescence, excellent stability and high affinity with ZEN (affinity constant was approximately 1.723 × 109 M−1), which can significantly improve the detection sensitivity. Impressively, a portable sensing system was developed by the integration of SAQDsRu-DICA with a smartphone-based readout. After optimization, this DICA indicated a limit of detection reaching down to 0.008 ng/mL (colorimetric mode) and 0.0058 ng/mL (fluorescent mode), which were much lower than that of conventional gold nanoparticles-based ICA (0.1029 ng/mL), possessing favorable specificity and repeatability (relative standard deviation (RSD)