A simple and effective direct competitive chemiluminescence immunoassay for the detection of 4 kinds of quinolone antibiotics in milk was established using Nor-Biotin (biotin-modified norfloxacin [NOR]) bifunctional ligand and alkaline phosphatase–conjugated streptavidin signal amplification technology. The polyclonal antibody was obtained after the immunization of New Zealand White rabbits using norfloxacin-derived antigen. “Click chemistry” was used for the rapid and facile synthesis of the Nor-Biotin bifunctional ligand. After the optimization of the incubation time and reaction buffer, the direct competitive chemiluminescence assay method was developed and used for sensitive detection of 4 kinds of quinolone drugs (NOR, pefloxacin, ciprofloxacin, and danofloxacin). The IC50 of the 4 kinds of quinolone drugs ranged from 7.35 to 24.27 ng/mL, and the lowest detection limits ranged from 0.05 to 0.16 ng/mL, which were below their maximum residue levels, approved by the EU for treatment of food-producing animals. To demonstrate the applicability of the assay, artificially contaminated milk samples with the 4 quinolone drugs were analyzed. The mean recovery rates of the drugs ranged from 86.31% to 112.11%.

Antigen detection provides rapid and convenient diagnosis of respiratory infections. This study develops an innovative dual-fluorescence aptasensing method based on polydopamine-functionalized MXene (PDA-MXene) for the simultaneous detection of spike protein and hemagglutinin protein. The method employs green- and red-emitting quantum dot (QD) probes as fluorescence reporters, and the PDA-MXene as an effective adsorption and separation substrate. Coupled with a centrifugation-assisted separation strategy, this design method reduces background interference and enhances detection reliability. The method demonstrates good analytical performance, with detection limits of 0.82 ng/mL for spike protein and 2.11 ng/mL for hemagglutinin protein in single-channel mode. The dual-channel mode enables reliable and simultaneous quantification of both target proteins with minimal spectral cross-talk. Furthermore, this method exhibits high specificity against interferents including ions, proteins, and toxins. Artificial saliva, chosen as real sample, is spiked with target proteins to investigate the practical applicability of the method, showing recovery rates for both target proteins between 100 and 114 sensing strategy is simple to operate and allows the detection of new targets by simply replacing the azide-modified aptamer lyophilized powder. It therefore holds promising application for the simultaneous detection of multiple proteins in point-of-care testing and health monitoring fields.